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Estudio de catalizadores basados en platino para la reacción de PROX: influencia de los depósitos de carbono.

Castillo Barrero, Rafael · 2018

Abstract

In the Hydrogen technology, the preferential oxidation of CO in excess of hydrogen (PrOx reaction) is an important process for obtaining CO-free hydrogen for proton exchange membrane fuel cells (PEMFCs). PtCu based catalysts are one of the most studied systems for mobile devices because of their high activity/selectivity balance and their appropriate chemical and mechanical properties for the start-up/shut-down procedures during fuel processors operation conditions. Recently, the use of Pt-Cu bimetallic catalysts with excellent activity and selectivity towards CO oxidation was reported for PrOx reaction. However, there are not clear evidences off the nature of the active phases and the role of both metals during the reaction. To understand this system it is necessary to create a model catalyst which facilitates the study. Thus, well-defined Pt-Cu bimetallic alloy nanoparticles were synthetized and studied by Operando techniques allowing the comprehension of the surface electronic modifications in the solid-gas interface of the above mentioned model catalyst under PrOx reaction conditions. In this work, the composition and nature of the species present on the catalyst surface upon well-controlled reaction conditions were studied, in particular from the point of view of surface dynamics, structural transitions and the possible effects of reaction atmosphere and adsorbed overlayers on the surface composition and structure of the alloy.

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Estudio de catalizadores basados en platino para la reacción de PROX: influencia de los depósitos de carbono.

Author: Castillo Barrero, Rafael
Year: 2018
Source: https://idus.us.es/bitstreams/9b6ece1f-ba0b-4008-bc82-860eb7c59478/download
Es udio De Ca alizado es Basados En
Pla ino Pa a La Reacción De PROX:
In luencia De Los Depósi os De Ca bono
Es udio De Ca alizado es Basados En
Pla ino Pa a La Reacción De PROX:
In luencia De Los Depósi os De Ca bono
D. Ra ael Cas illo Ba e o
Tesis Doc o al
2015-2018
Uni e sidad de Se illa
&
No mandie Uni e si é
A mis dos mad es.
La que nunca se ue y la que me besa odas las
noches
Main Mo i a ion.
Es udio De Ca alizado es Basados En
Pla ino Pa a La Reacción De PROX:
In luencia De Los Depósi os De Ca bono
Main mo i a ion
I
Low wo king empe a u es, high ene gy densi y, low weigh , compac ness o apid
s a -up/ Shu -down cycles doing Polyme -elec oly e memb ane uel cell (PEMFC)
de elopmen esea ch is one o he mos a ac i e opics in he sea ch o clean ene gy
o mobile de ices. Hyd ogen low om he hyd oca bon e o ming eed he PEMFC.
Howe e , e o ming p ocess in ol e signi ican amoun o ca bon monoxide o ma ion
ha mus be educed below 10 ppm o a oiding he poison o he P ca alys on he uel
cell anode su ace. Ca aly ic me hana ion p ocess and p e e en ial oxida ion o CO in
excess o H2 s eam (P Ox eac ion) ha e been conside a e he mos p omising ways o
ob aining CO- ee hyd ogen low1,2. In he case o P Ox p ocess, wo compe i i e
eac ions a e in ol ed:
(1) CO +
O2 → CO2 H = -283 kJ/mol
(2) H2 +
O2 → H2O H = -242 kJ/mol
P based ca alys s p esen no iceable PROX ac i i ies, especially low loading P /Al2O3
ca alys s3. Manasilp e al.4 obse ed CO con e sions a ound 80% a 170ºC wi h
selec i i y alues o 50%. Howe e , hey p obed he d ama ically CO con e sion
dec emen wi h he inc emen o CO2 concen a ion. Conside ing his wo k,
A gou opoulos e al.5 epo ed a P /Al2O3 Ca alys wi h 100% o CO con e sion o a
leas 110 h a 100ºC in a eac ion low composi ion o 1% CO, 1.25% O2, 50% H2, 15%
CO2 and he balance He.
On he o he hand, Cu based ca alys also p esen excellen ca aly ic p ope ies o he
p e e en ial oxida ion o CO. T. Reina e al.6 ca ied ou a compa ison o CuOCeO2
based ca alys s beha io in he CO clean up eac ions (WGS and P Ox). They epo ed
CuOCeO2/Al2O3 se ies ca alys wi h ull con e sion and selec i i y a 130ºC o P Ox
eac ion.

Main mo i a ion
II
Nowadays, ca alys s de elopmen o P Ox eac ion applied in mobile de ices is
ocused in Pla inum ca alys s modi ied by coppe p omo e s which exhibi a ema kable
enhanced o he P Ox ac i i y and selec i i y in he wo king empe a u e o PEMFCs1.
Koma su e al.7 showed he di e en ca aly ic beha io o P /Al2O3, Cu/Al2O3 and
P Cu/Al2O3 ca alys s ( igu e A). Those au ho s concluded ha hanks o he
elec ophilic cha ac e o he alloy coppe a oms in he p esence o CO, P Cu/Al2O3
ca alys ge ull con e sions and highe selec i i y alues han he monome al ca alys s
suppo ed on Al2O3.
Figu e A. Ca aly ic ac i i y e olu ion o P /Al2O3, Cu/Al2O3 and P Cu/Al2O3 ca alys s.
The applica ion o P Cu/Al2O3 ca alys s in mobile de ices do necessa y he condi ioning
ca alys in own eac ion mix u e a mosphe e. Fo ha , R. Fa au o3 pa en ed he
o mula ion o P Cu/Al2O3 sys ems wi h almos 1:3 s oichiome ic a io wi h ex emely
high ca aly ic ac i i y and selec i i y o CO2 a e condi ioning ea men in he eac ion
mix u e en i onmen .
Howe e , he wonde ul pe o mance o P Cu3/Al2O3 ca alys s is no o ally con olled.
P e ious wo ks ca ied ou in ou g oup by Rome o-Sa ia e al.8 concluded ha
Main mo i a ion
III
P Cu/Al2O3 ca aly ic beha io depends o condi ioning ea men s pa ame e s and
eac ion mix u e composi ion. Those au ho s showed he e ec o condi ioning
ea men a mosphe e, he hea ing a e in he condi ioning ea men and he eac ion
mix u e composi ion in he CO con e sion ( igu e 1.B).
Figu e B. In luence o condi ioning ea men pa ame e s in he ca aly ic ac i i y o P Cu3/Al2O3. A
compa ison o he CO con e sion a e condi ioning ea men a 200ºC (line ed) and 300ºC (blue line) is
shown (a). Figu e A.b. shows he CO con e sion as a unc ion o he condi ioning ea men hea ing a e.
Figu e B.a. shows he e iden e ec o he condi ioning ea men pa ame e s in he
ca aly ic ac i i y o his sys em. In e es ing, lowe condi ioning ea men empe a u es
in ol e highe CO con e sion while highe hea ing a es supposed an enhanced o he
ca aly ic beha io ( igu e B.b). Pa allel, CO con e sion o P Cu3/Al2O3 ca alys as a
unc ion o he condi ioning ea men en i onmen is shown in igu e XX.
Main mo i a ion
IV
Figu e C. CO con e sion o P Cu3/Al2O3 as a unc ion o he condi ioning ea men en i onmen .
Figu e C. shows he high e ec in he CO con e sion o he condi ioning ea men
a mosphe e. Oxidizing en i onmen p esen s lowe CO con e sion alues wi h an
almos inc easing linea end as a unc ion o he empe a u e. When condi ioning
en i onmen is mainly composed by educe a mosphe e ( eac ion mix u e is 50% H2),
ca aly ic ac i i y ob ains CO con e sions abo e 75% a 120ºC. F om his poin , CO
con e sion eaches chemical equilib ium alues. Mo eo e , second eac ion cycles
mean highe ini ial CO con e sion alues in all he samples p e ea ed unde educe
a mosphe es.
T ying o unde s and he un ypical ca aly ic beha io , S. Palma9 ca ied ou a simula ion
o he condi ioning ea men unde eac ion mix u e a mosphe e by ope ando FTIR
( igu e D).
Main mo i a ion
V
Figu e D. FTIR spec a o P /Al2O3 ca alys su ace submi ed o di e en empe a u es unde a eac ion
mix u e composi ion o 50% H2, 0.25% CO, 0.5% O2, 17% CO2, 15% H2O and N2 balance. Condi ioning
ea men a 200ºC wi h hea ing a e o 15 ºC/min. Red spec um was acqui ed be o e he ea men unde
A a mosphe e. Blue colo spec a we e aken du ing he amping empe a u e and g ey colo spec a a e
he empo al su ace e olu ion unde eac i e low a 200ºC.
They ound ini ial bands a 1460, 1574, 2976 and 2931 cm-1 co espond o abso bed
ace a es species om he syn hesis s ep. Ca alys s we e syn he ized by suppo
imp egna ion wi h ace ic acid. When ca alys was exposed unde eac ion en i onmen ,
bands cha ac e is ic o CO2 gas phase and a new band a 2032 cm-1 assigned o CO
abso bed on me allic pla inum become e iden . Du ing he iso he mal pe iod a 200ºC,
di e en su ace modi ica ions we e obse ed. Fi s , he band a 2032 cm-1 was shi ed
o 2028 cm-1 while new bands a 2870, 2927 and 2967 cm-1 co espond o ν(CH)
s e ching ib a ional modes inc ease wi h ime. They ela ed i wi h he p esence o
su ace ca bon deposi s, om he educe o capping agen s used in syn hesis s ep
p e iously de ec ed, which a e hyd ogena ed due o he high H2 concen a ion in he
eac ion mix u e. The inc emen o hyd oca bons species on he su ace ca alys
in ol es an elec onic in e ac ion wi h he me allic si e showed by he shi o lowe
Chap e 1.
Expe imen al
Es udio De Ca alizado es Basados En
Pla ino Pa a La Reacción De PROX:
In luencia De Los Depósi os De Ca bono

Expe imen al
7
1.1 Ambien P essu e XPS
X-Ray pho oelec on spec oscopy (XPS) p o ides essen ial in o ma ion o he o al
unde s anding o ma e ials. Elemen al composi ion, oxida ion s a e o he su ace o
su ace dynamics could be elucida ed by his echnique.
XPS is based on he pho oelec ic e ec 1. Figu e 1.1 shows a schema ic illus a ion o
he pho oemission p ocess. Inciden ene gy exci es an a om which abso bs a pho on o
ene gy hν. Then, co e elec on o binding ene gy Eb wi h espec o he Fe mi Le el EF
is ejec ed wi h kine ic ene gy EK by Eq (1.1):
Ek = hν - Eb - (1)
Whe e Ek is he kine ic ene gy o he pho oelec on, h is he Planck´s cons an , ν is he
equency o he exci ing adia ion and is he wo k unc ion o he spec ome e .
Figu e 1.1.Schema ic Pho oemission p ocess illus a ion.
XPS has been adi ionally pe o med unde ul a-high acuum condi ions (UHV).
Howe e , M. Salme on and R. Schlo gl2 designed a new ool o su ace science and
ca alysis b eaking he p essu e gap be ween he wo king condi ions and he UHV
condi ions in he analysis chambe o he con en ional XPS sys em. They de eloped a
di e en ially pumped elec on ene gy analyze which is able o acqui e spec a unde
wo king condi ions a p essu es om UHV o almos 20 milliba a he same ime ha
Expe imen al
8
he UHV condi ions is keeping in he de ec o . This de elopmen allows he s udy os
solid-gas in e aces unde wo king condi ions and i was called “Ambien p essu e X-
ay pho oelec on spec oscopy”.
The APXPS expe imen s o he p esen manusc ip we e ca ied ou in CIRCE beamline
o he ALBA synch o on ligh sou ce (Ba celona, Spain). PHOIBOS 150 NAP elec on
ene gy analyze (SPECS) equipped wi h di e en ial pumping sys em was employed.
The wo king p essu e ange in ol es om UHV o 20 mba . Synch o on adia ion
p o ides e y high pho on lux han in con en ional sou ces which leads o acqui ed
spec a wi h highe esolu ion. CIRCE beamline is an undula o beamline wi h pho on
ene gy ange 100-2000 eV. The beam spo size a he sample is 20 x 100 m2. Spec a
we e acqui ed wi h pass ene gy o 20 eV which leads o ene gy esolu ion lowe han
300 meV ull wid h a hal -maximum (FWHM)3,4.
Figu e 1.2.a) CIRCE Beamline a ALBA synch o on ligh sou ce. b) PHOIBOS 150 NAP elec on
ene gy analyze (SPECS) equipped wi h di e en ial pumping sys em
Expe imen al
9
1.2 CO as P obe molecule
Besides o he non- eac i e cha ac e and he high quali y in o ma ion ha can be
eco ded by he use o his p obe molecule, he ib a ional spec um o CO is simple.
The (CO) s e ching ib a ion mode and he ex inc ion coe icien depend o he
o med bond na u e wi h he su ace.
Elec onic s uc u e o CO based in sp hyb idiza ion. In igu e 1.3 can be obse ed he
illing o bonding o bi als , 4 and 1 (1 x and 1 y) and he an i-bonding o bi al 5
as well as he emp y molecula o bi als 2 and 6 . The e o e, highes occupied
molecula o bi al (HOMO) is he an i-bonding o bi al 5 and he low unoccupied
molecula o bi al (LUMO) a e he degene a ed 2 o bi als5.
Figu e 1.3. Molecula o bi al diag am o CO. 1s o bi als o ca bon and oxygen called 1 and 2 a e no
shown.
A e , CO in e ac s wi h me al ions by h ee possible pa hway; simple elec os a ic
in e ac ion o he CO molecule wi h he ield o he ca ion, by o ma ion o bonds
Expe imen al
10
wi h CO as elec on dona o and inally, by o ma ion o bonds wi h CO as elec on
accep o 6.
Elec os a ic in e ac ion o he cha ge dis ibu ion o he CO molecule and he ield o
he ca ion e ec s a e connec ed wi h s abiliza ion o all o bi als o CO in he posi i e
elec os a ic po en ial gene a ed by he ca ion. I con ibu es wi h a posi i e cha ge o
he in e ac ion ene gy which is also compensa ed by he Pauli epulsion be ween he
elec ons o bi als o he ca ion and CO co e age7.
Howe e , acco ding wi h he F on ie o bi als app oach, he mos impo an in e ac ion
in he CO coo dina ion o ca ionic cen e s occu s be ween hei HOMO and LUMO
when he symme y o he co esponding o bi als i s. Fo ha , i s ake place he
in e ac ion be ween he HOMO o CO (an i-bonding o bi al 5 ) and LUMO o he
me al ca ion wi h a sui able spa ial o ien a ion. As a consequence, a new bonding and
an i-bonding molecula o bi als a e o med8,9. Then, ake place he second pa o he
on ie o bi al in e ac ion. I is based in he in e ac ion be ween he HOMO o he me al
ca ion (dxz and dxy o bi als) and he LUMO o he CO ligand molecule (an i-bonding 2
o bi als). In his case, a new bond is o med leading a ans e o elec on densi y
om he me al ca ion o he ligand which is known as -backdona ion ans e ( igu e
1.4). The s eng h o he new bond depends o he si e elec on densi y, since elec on
densi y inc eases, he bond s eng h inc eases. The e o e, an impo an syne gis ic
e ec o and bonds is obse ed. The bonds o ma ion in ol e an elec on
en ichmen o he me al ion which means s onge bonds o ma ion while a he same
ime, o ma ion o bonds ans e elec on densi y om he me al ca ion o he CO
molecule meaning s onge bonds.
Expe imen al
11
Figu e 1.4. Schema ic ep esen a ion o he o bi al in e ac ions in he o ma ion o and bonds
be ween CO ligands and he me al ca ion.
S ong shi s o he abso bed ca bonyl on he me allic si e a e obse ed due o he
di e en na u e o he bonds. This make possible he s udy o he di e en p ope ies
(coo dina ion si e geome y, oxida ion s a e, acidi y,…)10.
In si u FTIR sys em
The ypical in si u FTIR sys em ( igu e 1.5) is composed by almos h ee big
compounds; a glass accum sys em, an IR cell and he spec ome e .
Figu e 1.5. In si u FTIR sys em.

Expe imen al
12
Glass sys em is connec ing o wo acuum pumps which keep he sys em unde p essu e
om 10-3 mba o ul a-high acuum a ound 10-7 mba . P obe molecules as well as
di e en gases o he condi ioning ea men a e in oduced in he sys em by wo SVT
al es. Desi ed gaseous amoun is con olled by wo acuum gauges wi h di e en
measu emen anges. Gases e acua ion is ca y ou by he acuum sys em h ough
liquid-ni ogen aps.
Also IR cell can be sepa a ed in h ee compounds ( igu e 1.6); bo om pa , op pa and
he sample holde . KB windows, o en and he mocouple a e loca ed in he qua z
bo om pa which joining wi h he op pa , based in glass squa ed pipe, by i on o- ing.
He e, he used small olume in he p obe molecule adso p ion by small doses is loca ed.
The con olled olume is spli and dosed by SVT al es. Finally, spec ome e is a
Nicole 6700 Fou ie T ans o m IR spec ome e equipped by DTG de ec o (Deu e
T iglyce ide sulpha e). Spec a we e collec ed by 128 scans wi h 4 cm-1 o esolu ion.
Figu e 1.6. IR cell scheme.
Expe imen al
13
REFERENCES
(1) Nieman s e d ie , J. W. Spec oscopy in Ca alysis; 2007.
(2) Salme on, M.; Schlögl, R. Su . Sci. Rep. 2008, 63, 169–199.
(3) Huck-I ia , C.; Sole , L.; Casano as, A.; Ma ini, C.; P a , J.; Llo ca, J.;
Escude o, C. ACS Ca al. 2018, 8 (10), 9625–9636.
(4) Pé ez-Dies e, V.; Aballe, L.; Fe e , S.; Nicolàs, J.; Escude o, C.; Milán, A.;
Pelleg in, E. In Jou nal o Physics: Con e ence Se ies; 2013; Vol. 425.
(5) Wes , A. R. Solid S a e Chemis y and i s applica ions.
(6) Hadjii ano , K. I.; Vayssilo , G. N. Ad . Ca al. 2002, 47, 307–511.
(7) Pacchioni, G.; Cogliand o, G.; Bagus, P. S. In . J. Quan um Chem. 1992, 42,
1115–1139.
(8) Hadjii ano , K. I.; Vayssilo , G. N. Ad . Ca al. 2002, 47, 307–511.
(9) Fe a i, A. M.; Neyman, K. M.; Rösch, N. J. Phys. Chem. B 1997, 101 (45),
9292–9298.
(10) Dominguez-Ga cia, E. E e du suppo su la mo phologie e l’ac i i é des
ca alyseu s d’hyd odésul u a ion, Uni esi y o No mandy, 2017.
Chap e 2.
Syn hesis o P Cu3 Nanopa icles:
A New Su ace Cleaning Me hod
Es udio De Ca alizado es Basados En
Pla ino Pa a La Reacción De PROX:
In luencia De Los Depósi os De Ca bono
Syn hesis o P Cu3 nanopa icles: a new su ace cleaning me hod
15
2.1 In oduc ion
Nanopa icle size and shape s ongly in luences he physical and chemical p ope ies o
ca alys s. Fo ins ance, in an ea ly s udy Na ayanan and El-Sayed analyze he in luence
o P and Pd monome allic nanopa icles shape on he ca aly ic decomposi ion o
oxala e and in Suzuki c oss-coupling eac ions1.These au ho s ela ed he obse ed
ca aly ic di e ences wi h he popula ion o s ep and co ne si es o he nanopa icles
and, he e o e, he pa icle size also a ec s he ca aly ic ac i i y on modi ying he
ela i e p opo ion o hese si es. Lang e al.2 demons a e using DFT analysis o he CO
oxida ion on Pd clus e s ha he di e ences in CO binding ene gies in Pd(111) single
c ys als and small Pd clus e s de e mine he eac ion pa hs and in consequence he
ca aly ic ac i i y.
These size e ec s ha e been also obse ed o gold nanopa icles suppo ed on ca bon.
Megias-Sayago e al.3 ound a s ong co ela ion be ween pa icle size and shape and he
ca aly ic ac i i y o he oxida ion o glucose o gluconic acid.
Rea angemen s o he ca alys su ace du ing eac ion ha e been obse ed o
bime allic RhPd and P Pd nanopa icles du ing e hanol s eam e o ming. The su ace
composi ion is al e ed as a unc ion o he gaseous en i onmen 4. In he case o
monome allic pa icles, he di e en eac i i y o s ep and co ne si es may esul in a
shape modi ica ion and hence on he ca aly ic ac i i y1. A ee ene gy dec ease upon
adso p ion o molecules is esponsible o su ace modi ica ions upon exposu e o
di e en gaseous en i onmen s. The ene gy gained by o ming coppe -ca bonyl clus e s
on he su ace o Cu (111) d i es he econs uc ion p ocess5.
Me allic nanopa icles a e usually syn hesized om sal s solu ions con aining he me al
o in e es . Roucoux e al.6 p o ided a comp ehensi e e iew on syn he ic me hods o
Syn hesis o P Cu3 nanopa icles: a new su ace cleaning me hod
22
suppo and he ex emely low speci ic su ace (a ound 8 m2/g) may acili y he
mo phological s udy by HRTEM.
TEM images e eal a monomodal sha p size dis ibu ion o almos sphe ical
nanopa icles wi h an a e age diame e o 3.0 nm (Figu e 2.5).
Figu e 2.5. (a) HRTEM image o P Cu nanopa icles alloy. (b) P -Cu nanopa icles alloy size
dis ibu ion. (c) and (d) STEM images P Cu3/ Al2O3
Figu e 2.5c and 2.5d show a clea c ys allog aphic s uc u e and he exhibi ed spo s
obse ed in he Fou ie ans o m images (no shown) o some o he singles P Cu3
nanopa icles we e s udied. The in e plana spacing o he obse ed nanopa icles is
a ound 2.17 Å, co esponded o (111) planes o he P Cu alloy wi h FCC s uc u e while
he in e plana dis ances o P FCC and Cu FCC show spo s a 2.27 and 2.09 Å.

Syn hesis o P Cu3 nanopa icles: a new su ace cleaning me hod
23
2.2.2 A new su ace cleaning me hod
Howe e , he ob ained nanopa icles may ha e capping agen s/ca bonaceous esidues
and ace elemen s om he educing agen s on he nanopa icles su ace.
Figu e 2.6. HAADF-STEM image o P Cu3 nanopa icles suppo ed on Al2O3 and elemen al map o he
single elemen .
High Angle Annula D ak ield Scanning T ansmission Elec on Mic oscopy (HAADF-
STEM) mode allows he s udy o me allic nanopa icles suppo ed in low-Z a oms
( igu e 2.6). A he same ime, EDS analysis was ca ied ou . The analysis e eals he
homogenous pla inum and coppe dis ibu ion on he suppo as well as he p esence o
ca bon deposi s associa ed o he P Cu me allic phase.
The e o e, a ca e ul s udy o he p esence o hese o e laye s and he p ocedu es o
emo e hem a oiding any al e a ion o he nanopa icles size and mo phology was
Syn hesis o P Cu3 nanopa icles: a new su ace cleaning me hod
24
ca ied ou . Fi s a all, a he mal deso p ion expe imen allows o de ec he p esence o
capping/sol en molecules on he nanopa icle su ace. Mass spec ome ic analysis o
he e ol ed gases e eals a complex decomposi ion pa e n o he emaining molecules
a he su ace. Fo he sake o simplici y jus mass- o-cha ge 16, 18, 28, 41 and 44 a ios
a e plo ed ( igu e 2.7).These m/z a ios a e assigned o he e olu ion o me hane, wa e ,
ca bon monoxide, me hyl isocyanide, a p oduc o he educ ion o PVP, and ca bon
dioxide.
The measu emen s o he nanopa icles TPD was ca ied ou using an A 50ml/min low
and hea ing o 800 (10 /min). 20 mg o sample we e placed in a U-shaped qua z
eac o .
Figu e 2.7. Tempe a u e p og ammed deso p ion – mass spec oscopy o P Cu3 om he oom
empe a u e o 800ºC. Black line a 350ºC ep esen s he beginning o pla inum sin e ing empe a u e.
Syn hesis o P Cu3 nanopa icles: a new su ace cleaning me hod
25
The decomposi ion o PVP is ca alyzed by P ha educes i s decomposi ion
empe a u e18 s a ing a 350ºC; mo eo e , in he p esence o P PVP deg ada ion
accoun s jus o ca. 69% weigh loss while pu e PVP decomposes almos comple ely
(>95% weigh loss). Al hough, he main mechanism o decomposi ion is assumed ha
is he depolyme iza ion he o ma ion o amo phous ca bon ha emains on he P
su ace has been epo ed by Bo odko e al.19. The obse ed p o iles wi h signi ican gas
e olu ion 300 and 450ºC o CO and me hylsocyana e accoun s o PVP decomposi ion;
he low empe a u e e olu ion o H2O and CO2 may be indica i e o he p esence o
e hylene glycol molecules on he nanopa icles su ace. Gas e olu ion is obse ed a
empe a u es as high as 800ºC indica ing ha o ganic agmen s emain on he su ace
and no only amo phous ca bon. The mal ea men s a hese empe a u es should esul
in nanopa icle sin e ing and mus be disca ded.
Low empe a u e ai calcina ion o he nanopa icles was a emp ed o ge nanopa icles
ee o ca bonaceous esidues. Figu e 2.8 shows he P Cu3 nanopa icles in si u XRD
da a ob ained du ing an oxidizing ea men in an O2- ich a mosphe e om RT o
350ºC. A 220ºC is clea ly e iden om he igu e a coppe seg ega ion p ocess
ob aining oxidized species o coppe (co espond o monoclinic sys em c ys alline and
C2/C symme y) and P xCu3-xO species ( e agonal s uc u e)20. A 350ºC (ac i a ion
p ocess empe a u e)21, P Cu alloy is comple ely seg ega e o me allic pla inum species
and CuO. The nanopa icles size inc ease un il 20 nm.
N
Syn hesis o P Cu3 nanopa icles: a new su ace cleaning me hod
26
Figu e 2.8. In si u-XRD da a o P 1Cu3 nanopa icles ob ained unde O2- ich a mosphe e.
I is clea e iden om he igu e he o ally seg ega ion o he me als o me allic
pla inum, oxidized coppe species and a new P xCu3-xO solid solu ion20 o med by
se e al compounds membe ( om x=0.135 o x=0.355). The na u e o he seg ega ed
phases was analyzed by peak decon olu ion. The analysis e eals ha he ob ained
me allic pla inum phase is highly c ys alline and also, a ema kable g ow h o he
pa icle size, especially o he oxidized coppe species (20 nm).
To a oid hese p obable cases and o emo ing he es o PVP om he syn hesis
p ocess, an al e na i e cleansing s ep based in he PVP ligands exchange o o he s kind
o ligands, which could be emo ed a low empe a u e, was designed. In his cleansing
s ep consis ed in wash p ocess o he nanopa icles wi h a mix u e o ace ic acid, wa e
and ace one. This s ep akes place be o e he condi ioning p ocess.
The ollow up p ocess was measu ed by UV-Vis spec oscopy o he supe na an seeing
how he abso p ion bands changed ( igu e 2.9). The expe imen al abso p ion band
shows a maximum a 242 nm assigned o he π→ π* elec onic ansi ion o C=O and
C=C g oups o he PVP molecules a ound a he me allic si e. Fu he mo e, i is
Syn hesis o P Cu3 nanopa icles: a new su ace cleaning me hod
27
app eciable a shoulde a 300 nm assigned o cha ge- ans e ansi ions o exci ed
elec ons om ca bonyls g oups o acan d o bi als o he bime allic nanopa icles19.
The main band a 242 nm will su e changes while PVP molecules a e being emo ed
wi h successi e cen i uge p ocesses (cycles) coming om he su ace o he
nanopa icles. The mo e p ocesses ha ake place, he band will be close o a alue o
234 nm which co esponds o he Acid/H2O mix u e22 since mos o he PVP ha could
be le on he nanopa icles would ha e been washed. As seen in igu e 2.9, he mo e
cen i uge p ocesses ha he nanopa icles su e , he band om he supe na an washed
liquid acqui e a shape close o ha o he cleansing mix u e.
Figu e 2.9. UV-Vis spec a o P Cu3 nanopa icles cleaning liquid a e he di e en pu i ica ion s ep;
ace ic acid/ wa e (black), PVP (yellow), supe na an a e i s pu i ica ion ( ed), a e second pu i ica ion
(blue) and a e hi d pu i ica ion (g een).
This could be due o he ac ha he cleansing was success ul. In o de o p o e his,
he TPD-SM was epea ed on he now clean hyd ogena ed nanopa icles (no shown).
The m/z alue o 41 (which co esponds o he p oduc o he educed PVP) is no longe
p esen . As a esul o his ligand exchange and conside ing he esul s o he second
TPDS-SM ca ied ou , ace a es may be p esen in he su ace o he nanopa icles.

Syn hesis o P Cu3 nanopa icles: a new su ace cleaning me hod
28
The analysis o he nanopa icles su ace by a speci ic and e y sensi i e echnique as
APXPS con i ms a ema kable ca bon signal. The ca bonaceous laye ha co e s he
nanopa icles is clea ly e iden . The e o e, o ob aining a comple ely clean
nanopa icles su ace, di e en in-si u ea men s, a e ligand-exchange s ep, we e
s udied by APXPS. So ha , he p oposed su ace cleaning me hod is shown in igu e
2.10.
Figu e 2.10. Schema ic nanopa icles cleansing s ep.
The APXPS expe imen s we e ca ied ou a CIRCE beamline a ALBA synch o on
ligh sou ce. The spec a we e ob ained a X- ay pho on ene gy o 450 eV o C (1s) and
he inelas ic mean ee pa hs (IMFP) accoun o he chosen pho on ene gy is 0.45 nm in
o de o de ec jus he deposi ed ca bon on he su ace ca alys . Spec a we e e e ed o
he Fe mi Le el (see associa ed con en 2.5). The Cu (2p) and P (4d) APXPS spec a
we e acqui ed a he same kine ic ene gy. The p oposed ea men s we e: 750 mTo H2
a mosphe e, 750 mTo H2 and H2O (50:50), 750 mTo CO2, 750 mTo H2 (a e CO2
ea men ), 750 mTo CO2 and H2 (40:60). The sample holde empe a u e was 350ºC.
Figu e 2.11 shows he C (1s) signal e olu ion as a unc ion o he a mosphe e exposu e
and i is app eciable a subs an ial oscilla ion o he su ace ca bon amoun as he main
low changes. Only unde CO2 a mosphe e exposu e, he C (1s) signal disappea
Syn hesis o P Cu3 nanopa icles: a new su ace cleaning me hod
29
meaning he absolu ely emo e o he su ace ca bon, esul ing any addi ion o he main
ca bon dioxide a mosphe e an inc ease in he amoun o deposi ed ca bon.
Figu e 2.11. a) Rela i e su ace amoun o ca bon as a unc ion o he ac i a ion ea men . b) Cu (2p)
co e-le el APXPS spec a unde di e en in si u ea men s; acuum, 750 mTo H2, 750 mTo H2+H2O,
750 mTo CO2, 750 mTo H2 (a e CO2 ea men ), 750 mTo CO2 and H2 (40:60). c) P (4d) co e-
le el APXPS spec a unde di e en in si u ea men s. Inciden pho on ene gy is 1100 eV o Cu (2p)
and 485 eV o P (4d).
2.3 In luence o he su ace cleaning me hod in he elec onic
p ope ies o he su ace
On he o he hand, he new in-si u ea men o emo ing he su ace ca bon o e laye
canno be a ec ing he na u e o he ac i e si e. The no modi ica ion o Cu and P
species a e he CO2 ea men was con i med by he Cu (2p), P (4d) and P (4 )
APXPS spec a s udy.
Syn hesis o P Cu3 nanopa icles: a new su ace cleaning me hod
30
Sa elli e peaks cha ac e is ic o oxidized species o coppe a e no p esen du ing any
ea men s ( igu e 2.11.b) and Cu (2p3/2) peak binding ene gy co esponds o me allic
coppe species in all he cases. We can obse e ha Cu (2p3/2) peak o he esh sample
a 932.3 eV and when he sample is exposed unde H2 a mosphe e, he peak was shi ed
o 931.1 eV. La e , due o he oxidizing cha ac e o wa e showed by Sa ele a e al.23
in an elec ochemical s udy by APXPS, Cu (2p3/2) peak is shi ed o 932.3 eV al hough
he sa elli e peak is s ill no p esen . Unde he CO2 en i onmen , he main peak o Cu
(2p) is shi ed o 931.1 eV. The oxida ion s a e is he same bu he e is a clea elec onic
s uc u e modi ica ion clea ly in luence by he change o ex a-a omic con ibu ion
(change o neighbo a oms) in he inal s a e elaxa ion ene gy24. I is e lec ed in a
change o he me allic su ace composi ion as a unc ion o he exposu e en i onmen .
Figu e 2.12 shows he coppe /pla inum su ace a omic a io as a unc ion o he Cu
(2p3/2) peak binding ene gy and you can obse e a change o he s oichiome y on he
nanopa icles su ace om Cu1P 1 unde he mix u e o H2 and H20 a mosphe e o
Cu6P 1unde CO2 a mosphe e. The e is a clea ela ionship be ween he su ace
composi ion o he nanopa icles and he binding ene gy o he Cu (2p) pho oelec ons
om he su ace (IMFP = 4.5 Å); highe Cu/P a io means lowe Cu (2p) binding
ene gies. This end is o ally ela ed wi h he conclusions o Koma su e al.25. These
au ho s ca ied ou a compa a i e s udy be ween pla inum nanopa icles and P 1Cu1
alloy nanopa icles suppo on alumina as ac i e si e o he p e e en ial oxida ion o
CO. They obse ed by he CO adso p ion in bo h ca alys s by FT-IR, a change in he
equency o he adso bed CO in he me allic si e. When CO adso p ion was ca ied ou
in he P 1Cu1 su ace ca alys , hey obse ed a dec emen o he equency e e eed o
he P ca alys om 2049 cm-1 o 2009 cm-1. They ela ed his ac wi h an elec on
ans e om coppe a oms o pla inum si es in he P 1Cu1 which supposes a dec emen
Syn hesis o P Cu3 nanopa icles: a new su ace cleaning me hod
31
o he elec on densi y o he coppe a oms. In his way, highe su ace pla inum
concen a ion in ol es highe binding ene gies o Cu (2p) pho oelec ons om he
su ace o he nanopa icles.
Figu e 2.12. Coppe /pla inum su ace a omic a io as a unc ion o he Cu (2p3/2) peak binding ene gy.
Pho on ene gy o 1100 eV o Cu 2p was used o p oduce pho oelec ons wi h kine ic ene gy a ound 170
eV. The IMFP accoun he chosen pho on ene gy is 0.45 nm. Line g een ep esen s he linea i ing.
A e pumping he CO2 om he analysis chambe , nanopa icles we e exposed unde
H2 low and Cu (2p3/2) peak is no a ec ed. Finally, he addi ion o CO2 o he H2 low
supposed a so shi o highe ene gy o Cu 2p peak o 0.2 eV o 931.3 eV.
Compa ing he P (4d) peaks du ing he di e en ea men s ( igu e 2.11.c), P (4d)
signal is no app eciable un il he su ace ca bon o e lays emo al wi h he CO2
ea men , imp o ing hus he pla inum a ailabili y as ac i e si e. Any addic ion o he
931,0 931,5 932,0 932,5
0
1
2
3
4
5
6
7
H2+H2O
F esh
H2+CO2
CO2
H2
Cu / P (mola a io)
Cu (2p3/2) Binding Ene gy / eV
H2
(A e CO2)
0
1
2
3
4
5
6
7
Syn hesis o P Cu3 nanopa icles: a new su ace cleaning me hod
38
same way, when CO2 is added o he main H2 low, CO2 is also dissocia ed by hyd ogen
meaning he inc emen o he su ace ca bon amoun and showing he cha ac e is ic
peaks o CO2 (292.7 eV and 536.6 eV) and CO (291.0 eV and 537.7 eV) gas phases.
The CO gas o med by CO2 dissocia ion is adso bed in he me allic si es and he
cha ac e is ics peaks o he adso bed CO in he me allic si es a 286.1 eV and 286.9 eV
as well as he peak assigned o adso bed CO in elec on de icien coppe si es (533.4 eV
and 287.9 eV) a e shown again.
Addi ionally, igu e 2.16 shows a HRTEM image o P Cu3 nanopa icles alloy a e H2-
ich a mosphe e exposu e con i ming he p esence o he ca bonaceous laye ha co e
all he ca alys (no de ec able o con en ional echniques) while he image o P Cu3
nanopa icles alloy ea ed wi h CO2 p esen a ee-ca bon su ace.
Figu e 2.15. HRTEM images compa ison: a) P Cu3 nanopa icles alloy a e H2 ea men , b) P Cu3
nanopa icles alloy a e CO2 ea men .
2.4 Conclusions
Well-de ined P Cu bime allic alloy nanopa icles (1:3 mola a io) we e syn he ized and
cha ac e ized as a model ca alys o he p e e en ial oxida ion o CO. The p esence o

Syn hesis o P Cu3 nanopa icles: a new su ace cleaning me hod
39
su ace ca bon deposi om he use o o ganic capping agen s has been e idenced.
P e iously, he e ec o hese ypical ca bon deposi s in he ca aly ic ac i i y was
epo ed. Fo his eason, an al e na i e su ace cleaning me hod has been de eloped
which highligh ed he so condi ions and he non-e ec in he na u e o he ac i e si e.
Su ace dynamic du ing he p oposed p e ea men was s udied by ambien p essu e
XPS. Changes in he su ace es uc u ing we e obse ed in esponse o he exposed
en i onmen s. The su ace ca bon and oxygen species du ing he di e en condi ioning
ea men we e de ailed desc ibed o he unde s anding o he su ace d i en
es uc u ing o bime allic P Cu3 nanopa icles.
2.5 Associa ed con en
X- ay di ac ion (XRD):
To ge in o ma ion on he s uc u e and composi ion o he ob ained nanopa icles, X-
ay di ac ion (XRD) was employed. This analysis was pe o med on a X’Pe P o
PANaly ical di ac ome e . Di ac ion pa e ns we e eco ded using Cu Kα adia ion
(40 mA, 45 kV) o e 2θ ange o 5 - 90 and a posi ion-sensi i e de ec o using a s ep
size 0,05 and a s ep ime o 1200s.
T ansmission elec on mic oscopy (TEM):
The nanopa icles mo phology and size we e s udied by ansmission elec onic
mic oscopy (TEM) on a 200kV JEOL JEM-2010F ins umen wi h a s uc u al
esolu ion o 0,19 nm a Sche ze de ocus condi ions. To a oid he ca bon con ibu ion,
samples we e deposi ed di ec ly on o Ni g ids.
Ul a iole - isible spec oscopy (UV-VIS):
Syn hesis o P Cu3 nanopa icles: a new su ace cleaning me hod
40
The analysis o he supe na an washed liquid we e ca ied ou in an A an es A aLigh -
DH-S-BAL spec opho ome e equipped wi h an op ic ibe liquid senso o
wa eleng hs om 100 o 1000 nm.
Ambien p essu e X- ay pho oelec on spec oscopy (AP-XPS)
All ambien p essu e X-Ray pho oelec on spec oscopy (AP-XPS) expe imen s ha e
been pe o med a he AP-XPS ins umen ins alled a CIRCE beamline o he ALBA
Synch o on ligh sou ce (Ba celona, Spain). AP-XPS measu emen s we e ca ied ou
using a PHOIBOS 150 NAP Specs analyze equipped wi h ou di e en ially pumped
s ages. The beam spo size a sample is 100 x 20 μm2. AP-XPS da a we e acqui ed wi h
20 eV o pass ene gy and 0.1 eV o kine ic ene gy s ep. The wo k p essu e used was 5.0
x 1 mba (UHV) and 750 mTo o he ea men a mosphe es. The kine ic ene gy
o all he measu ed pho oelec on was a ound 170 eV and o aking accoun only he
su ace ca bon species, he pho on ene gy used o C (1s) was 450eV. Fo his ene gy,
he C (1s) elec ons IMFP (Inelas ic mean ee pa h) is 0.79 nm. In addi ion, he
employed pho on ene gies o he Cu (2p), O (1s), P (4d) and P (4 ) we e 1100 eV,
700 eV, 485 eV and 300 eV espec i ely. Fo he calcula ion o IMFP o his elemen s,
we employed he TPP-2M o mula p oposed by Tanuma e al.35 conside ing a closed
P Cu3 alloy (densi y o 12.08 g/cm3 and 43 alence elec ons pe molecule).
Consequen ly, he IMFPs o hese pho on ene gies is 0.45 nm.
The a omic a io o P , C and O we e ob ained conside ing he calib a ed P (4 5/2), C
(1s) and O (1s) peaks a eas. P e iously, a eas we e no malized by he inciden pho on
lux. A omic a io was calcula ed by he coe icien o no malized a ea o P (4 5/2) by
he o al a ea o P (4 5/2) and C (1s) o pla inum/ca bon a io and he no malized a ea
Syn hesis o P Cu3 nanopa icles: a new su ace cleaning me hod
41
o P (4 5/2) di ided by he sum o o al a ea o P (4 5/2) and O (1s) o pla inum/oxygen
a io.
Table S1. APXPS binding ene gies o he gas ma e . Sample wo k unc ion could a y
he alues.
H2O (g)
CO2(g)
CO (g)
C (1s)
-
292.7
291.0
O (1s)
535.5
536.6
537.7
* Binding Ene gy in eV
Table S2. APXPS binding ene gies and FWHM in O (1s) egion o he di e en ound
species.
A omic
Oxygen
Pu e
OH
OH
H2-bonding
CO/Cu
O Sub-
su ace
elec ophili
c a omic
oxygen
B.E. (eV)
529.9
530.4
530.9
531.5
531.5
531.5
FWHM (eV)
1.3
1.4
1.4
1.4
1.4
1.4
H2O
CO/P
CO/
B.E. (eV)
532.4
532.5
533.4
FWHM (eV)
1.4
1.4
1.4
Table S3. APXPS binding ene gies and FWHM in C (1s) egion o he di e en ound
species.
M-C
C-C
CHX
CO/Cu
CO/P
CO/
Sa elli e
B.E. (eV)
283.3
284.6
285.2
286.1
286.9
287.9
290.9
FWHM (eV)
1.2
1.2
1.2
1.2
1.3
1.3
2.5
Syn hesis o P Cu3 nanopa icles: a new su ace cleaning me hod
42
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Chap e 3.
S uc u al Changes Du ing
he Condi ioning T ea men
Es udio De Ca alizado es Basados En
Pla ino Pa a La Reacción De PROX:
In luencia De Los Depósi os De Ca bono
S uc u al changes du ing he condi ioning ea men
45
3.1 In oduc ion
Bime allic nanopa icles de elopmen becomes one o he mos impo an opics in he
ield o ca alysis. The gene al unde s anding o hese ma e ials goes h ough he con ol
o he nanopa icles composi ion, s uc u e, size o shape. The possibili y o a con ol
unable chemical composi ion o nanos uc u e and, he e o e, he possibili y o he
con ol o nanopa icles ca aly ic p ope ies opens an in e es ing way in he bime allic
nanoma e ials design. Fo ins ance, pla inum nanopa icles based ca alys s a e employed
in se e al eac ions o ob aining CO ee hyd ogen low om enewable sou ce1–5 and
Koma su e al.6 s udied how he coppe addi ion inc eases he ca aly ic ac i i y and
selec i i y owa d CO2 con e sion a lowe empe a u e in he p e e en ial oxida ion o
CO and Liu e al.7 showed how, due o he miscibili y and su ace ee ene gy o he
nanos uc u e compounds, he deposi ion sequence a ia ion o he change o
empe a u e and/o su ounding a mosphe e in he addi ion o he second me al in he
bime allic s uc u e b ing on he ob aining o di e en bime allic nanos uc u e, such as
co e-shell nanopa icles o nanoalloys.
Di e en nanos uc u e supposes di e en a omic coo dina ion o he ac i e si e.
Wanjala e al.8 s udied he co ela ions be ween he a omic s uc u e and he
elec oca aly ic beha io (mass ac i i y and speci ic ac i i y) o P NiFe/C ca alys o
oxygen educ ion eac ion (ORR). These au ho s showed by a de ailed XPS and XAFS
analysis he in luence o he p e- ea men empe a u e in he a omic s uc u e o he
syn hesized ca alys s. A highe mass ac i i y o he ca alys ea ed a low empe a u e
was obse ed while he ca alys ea ed a high empe a u e showed highe speci ic
ac i i y. They ela ed he di e en ca aly ic beha io o a change in he a omic s uc u e
S uc u al changes du ing he condi ioning ea men
46
om so co e-shell s uc u e wi h a P - ich su ace o a well-de ined P 46Ni22Fe32 by he
XPS analysis and he inc emen o he P -Ni(Fe) coo dina ion numbe s.
Figu e 3.1. In luence o he s uc u al ansi ions in he elec oca aly ic beha io o P NiFe/C ca alys o
oxygen educ ion eac ion.
In he same way, Zhang e al.9 desc ibe indings o op imizing he nanopa icles based
ca alys s. These au ho s showed he enhance o he ca aly ic ac i i y o ORR by he
uning nanopa icles s uc u e o co e-shell FeP /P ca alys ia co e s uc u al ansi ion
om ace cen e ed cubic (FCC) s uc u e o ace cen e ed e agonal (FCT) s uc u e.
Fo he o he hand, i is well-known ha he e a e non-con olle phenomena in
nanoalloy sys em such he su ace seg ega ion. Wang e al.10 explained his
phenomenon in PdxNi100-x alloy nanopa icles and hey obse ed a p e e en ially
mig a ions o he su ace o Pd, by he s ain ene gy e ec , o Ni in syn hesized alloy
wi h low alues o x due o he educ ion po en ial e ec . I supposed he loss o he
S uc u al changes du ing he condi ioning ea men
47
ini ial nanoalloy na u e. Howe e , Tao e al.11,12 opened a new way in he ield o
nanos uc u e enginee ing o nanopa icles wi h he con olle “su ace eac ion-d i en
es uc u ing phenomenon”. They exposed unde di e en in si u oxidizing o educing
su ounding en i onmen o RhPd and P Pd co e-shell nanopa icles and hey s udied by
ambien p essu e XPS (APXPS) he e e sible changes in composi ion and oxida ion
s a e in esponse o he en i onmen exposed.
Figu e 3.2. Re e sible changes un composi ion and oxida ion s a e in esponse o he en i onmen
exposu e o RhPd nanopa icles. Inelas ic mean ee pa h o 16 Å.
Ob iously, he es uc u ing phenomenon supposes a change in la ice spacing o he
nanopa icles. By abe a ion-co ec ed en i onmen al TEM, Xin e al.13 s udied he
a omic s uc u e o a single nanopa icle on 11 nm P 0.5Co0.5 alloy nanopa icles unde in
si u O2- ich and H2- ich en i onmen . Following he la ice spacing a ia ion unde
oxidizing en i onmen by HRTEM, hese au ho s obse ed he Co seg ega ion om he
single nanopa icle o ming cubic CoO islands on he su ace alloy. This ac means a
la ice spacing oscilla ion in he a omic laye s nea o he single nanopa icle su ace and
he main conclusion o he wo k is he seg ega ion p ocess e e sibili y since
S uc u al changes du ing he condi ioning ea men
54
3.2.3 Oxida ion s a e dynamics
The exis ence o di e en oxida ion s a es and he su ace dynamics du ing he
condi ioning p ocess could be hen elucida ed by ope ando synch o on-based X- ay
Abso p ion spec oscopy (ope ando XAS) s udy, which would be c ucial o obse e i
he su ace oxida ion s a es and/o he su ace dynamics di e om he bulk one. Fo
ha , XAS spec a o he samples we e eco ded a P L3-edge and Cu K-edge.
Conside ing he inal s a e (con ibu ions o he alence band and ex a-a omic
con ibu ions)25 by mul iple-sca e ing e ec s, Cu K-edge XANES spec a, based in
ansi ions om Cu 1s co e s a e o p symme y bound s a es, we e eco ded showing
he ea u es o elucida e he Cu mean oxida ion s a e and he local geome y. Figu e 3.6
shows no malized Cu K-edge XANES spec a eco ded upon he condi ioning p ocess
and i is clea e iden he ene gy o he Cu oil K-edge a ibu ed o 1s o 4p ansi ions
a 8981.3 eV (g ay dash line) as well as he 1s o 4pxy ansi ions a 8983.2 eV a ibu ed
o Cu+1 species ( ed dash line) and he 1s o 4pz ansi ions a 8985.6 eV a ibu ed o
Cu+2 species (yellow dash line)26.
The p esence o Cu2+ species is no aken accoun because he edge o oxidized species
appea a highe ene gies and he cha ac e is ic p e-edge peak o his kind o species a
8969 eV, a ibu ed o 3d o bi als pa ially occupied (dxy) which induce 1s→3d
ansi ion , is no p esen 27.
Taking accoun he edge ene gy and he line shape, he analysis o he Cu K-edge
spec a o he sample be o e and a e condi ioning p ocess is in ag eemen wi h he
p esence o me allic coppe species. A so chemical shi o 0.3 eV o highe ene gies
( e e eed o he Cu oil K-edge) was ound in he ene gy o he K-edge o he sample

S uc u al changes du ing he condi ioning ea men
55
be o e and a e he ea men . The e o e, in bo h cases he line shape o he Cu K-edge
spec a co esponds wi h he line shape o me allic Cu K-edge. Highe in ensi y o he
Cu K-edge a e he condi ioning ea men means an inc emen o he densi y o s a e
and he e o e, an inc emen o he elec onic densi y.
Figu e 3.6. a) Cu k-edge XANES spec a o coppe s anda ds and P Cu3 nanopa icles alloy be o e (blue
line) and a e (g een line) he condi ioning p ocess a 350ºC o 2 hou s. The inse shows a magni ica ion
o he 1s→3d ansi ion egion. 4b) k2-weigh ed FT o he EXAFS spec a.
Fo he o he hand, Choy e al.26 p oposed ha he ea u es o he sample a e he
condi ioning p ocess a 8993.3 eV co espond o he ansi ion │1s13d94
⟩ and he
abo e shoulde a 8998 eV is a ibu ed o ansi ions│1s13d94
⟩. These au ho s
s udied he Cu K-edge XAS spec a o well-de ined coppe con aining oxides ela ing
he shi in he ea u es a ibu e o non-degene a ed o bi als wi h changes in he
S uc u al changes du ing he condi ioning ea men
56
local symme y, acco ding o he c ys al- ield heo y, which suppose an elec onic
densi y oscilla ion. In his way, coppe a oms o he FCC s uc u e we e conside a e as a
cen osymme ic en i onmen wi h he local symme y o egula oc ahed on in he
second shell coo dina ion (dCu-Cu 2nd shell = la ice pa ame e ). Choy e al. explained ha
his ene gy shi o 2.8 eV o lowe ene gies o he ea u e a 9002.9 eV o me allic
coppe s anda d and he nanopa icles ea u e a 8999.0 eV is due o a change in he
local symme y om egula oc ahed on o me allic coppe s anda d o e agonally
dis o ed nea ly oc ahed on o he P Cu3 nanopa icles alloy.
Figu e 3.7 In ol ed ansi ions in Cu k-edge XANES spec a.
Howe e , i is necessa y conside e ha an oc ahed al complex used in c ys al- ield
heo y is modeled as six pa ial nega i e cha ge o an elec ic dipole ha in e ac
s ongly wi h he d o bi als o he cen al me al ion and, in his cases, all he coppe
a oms o he egula oc ahed on ha e he same elec ic dipole and he cha ges
in e ac ion is almos ze o. Thus, e e ed o he me allic coppe s anda d, i is clea
S uc u al changes du ing he condi ioning ea men
57
e iden ha he e is a change in he ene gy o he ea u e a ibu ed o
ansi ions│1s13d94
⟩ and his shi means a change in local geome y o he coppe
a oms by he p esence o pla inum in he alloy.
The P L3-edge XANES spec a be o e and a e he condi ioning ea men as
well as he heo e ical ansi ion a e shown in igu e 3.8. T. Anniye e a .28 s udied he
pla inum pa ial d-densi y o s a es in P Cu nanopa icles and hese au ho s explained
ha P L3-edge p obes he dipole allowed ansi ions (2p3/2→5d3/2,5/2) and he mos
in ense spec al ea u e, which ep esen s he unoccupied d-densi y s a es (whi e line), is
loca ed a 11566 eV. Only 5d5/2 co e le el has emp y s a es and he e o e, complying J
selec ion ules o he unoccupied d s a es ( = -1, 0, +1), a main ansi ion 2p3/2→5d5/2
is expec ed.
In his way, spec a be o e and a e condi ioning ea men show he same line
shape and he same ene gy o he whi e-line co espond o me allic pla inum species a
11566 eV in ag eemen wi h he las e e ed wo k. The in eg a ed a ea unde he P -L3
XANES spec um is p opo ional o he d-s a es popula ion29 and he e o e, he e is a
dec emen o d-s a es localized on P Cu3 nanopa icles a e he condi ioning ea men
by he P d-s a es hyb idiza ion wi h he alence o bi als o coppe (Cu 3d o bi als). This
means a ans e o d-holes in he elec onic densi y ansmission in he alloy du ing he
condi ioning ea men .
S uc u al changes du ing he condi ioning ea men
58
Figu e 3.8. No malized P L3-edge XANES spec a o he esh nanopa icles (blue line) and spec a o
nanopa icles a e he condi ioning ea men ( ed line). Dashed line show he s anda d o me allic
pla inum (g ey line) and oxidized species o pla inum (g een line and yellow line). Schema ic ansi ion
om p co e s a es o 5d s a es is ep esen ed in he igh side o he igu e
3.2.4 Local geome y s udy
In o de o iden i y wi h ela i e accu acy he s uc u al changes and he local
coo dina ion en i onmen o coppe and pla inum a oms, EXAFS unc ions analysis o
Cu k-edge and P L3-edge was pe o med in ALBA Synch o on Ligh Sou ce du ing
he in si u simula ion o condi ioning ea men .
A gene al ision o he di e en a omic shells su ounding o he coppe and pla inum
a oms is obse ed in he e olu ion o he Fou ie ans o m o he k3 weigh ed Cu k-
edge and P L3-edge EXAFS da a du ing he simula ion o he condi ioning ea men
( igu e 3.9).
S uc u al changes du ing he condi ioning ea men
59
Figu e 3.9. Fou ie - ans o med o he Cu k-edge EXAFS da a (k3-weigh ed) measu ed a oom
empe a u e om he P Cu3 nanopa icles be o e he condi ioning ea men ( ed line). Cu k-edge EXAFS
da a measu ed unde condi ioning ea men en i onmen a (a) 30ºC, (b) 150ºC, (c) 250ºC and (d) 350ºC.
The i ing o he EXAFS da a was ca ied ou using he mul iple-sca e ing FEFF6
heo y30 applied o a FCC s uc u e, wi h he a e age pa ame e s modula ion o
coo dina ion numbe (N), no malized dis ance (R) and he Debye-Walle ac o ( 2,
DWF) o each pa h31. FEFFs p o ided by he c ys allog aphy s uc u e o well-de ined
P Cu alloy 1:3 mola a io (JCPDS-00-035-1358).

S uc u al changes du ing he condi ioning ea men
60
.
Figu e 3.10. Cu k-edge EXAFS unc ion measu ed om nanopa icles be o e he condi ioning ea men
a oom empe a u e (a) and om nanopa icles a e he condi ioning ea men a 350ºC (b).
Figu e 3.11. P L3-edge EXAFS unc ion measu ed om nanopa icles be o e he condi ioning ea men
a oom empe a u e (a) and om nanopa icles a e he condi ioning ea men a 350ºC (b).
S uc u al changes du ing he condi ioning ea men
61
Conside ing he p oposed s uc u es models o P 34Cu66 nanoalloy o he esh sample
and su ace Cu- ich P 27Cu73 nanoalloy wi h gene ally FCC s uc u es o he sample
a e he condi ioning ea men , he p oposed i ing o Cu k-edge R-space da a is based
in he heo e ical con ibu ion o ou di e en pa hs consis en wi h a close P Cu3 alloy.
I means h ee di e en neighbo dis ances; i s coo dina ion shell o Cu-Cu and Cu-P
neighbo s a ound 2.6107 Å, second coo dina ion shell Cu-P dis ance a ound 3.6921 Å,
and hi d coo dina ion shell Cu-P and Cu-Cu dis ance a ound 4.5219 Å.
A alue o he ampli ude educ ion ac o
was de i ed om EXAFS da a analysis
and i was ixed o 0.92 (wi hin he heo e ical physical alues32). A ange o E0min= 2
eV and E0max= 15 eV o he edge ene gy a ia ion ( E0) was employed. Also, he
co ec ions o he model bond leng hs was a ied independen ly o he neighbo s o
coppe and pla inum calcula ions showing an inc emen o he alues a e he
condi ioning ea men . EXAFS i ing pa ame e s a e shown in able 1.
Table 1. EXAFS i ing pa ame e s o P L3-edge o he spec a collec ed be o e and
a e condi ioning ea men .
Cu-P
1s Shell
(NCu-P =2.6)
Cu-Cu
1s Shell
(NCu-Cu =6.3)
Cu-Cu
2nd Shell
(NCu-Cu=)
Cu-P
3 d Shell
(NP -Cu+ NCu-Cu =15)
d Cu-P
Cu-P
d Cu-Cu
Cu-Cu
d Cu-Cu
Cu-Cu
d3 d Shell
3 d Shell
Be o e
2.6215
0.0071(2)
2.6206
0.0177(8)
3.7020
0.1584(9)
4.5318
0.0995(2)
A e
2.6247
0.0108(2)
2.6107
0.0261(1)
3.6921
0.0331(7)
4.5219
0.0033(4)
*dis ance uni s: Å
S uc u al changes du ing he condi ioning ea men
62
Analyzing he i ing pa ame e s we can conclude di e en hings. Fi s o all, i s -shell
coo dina ion numbe o Cu a oms sugges a nons a is ical dis ibu ion en i onmen and
he a e age coo dina ion numbe o he abso bing Cu cen e is o med by 6.3 Cu
neighbo s a oms and 2.6 P neighbo s a oms which ag ees wi h he heo e ical FEFF o
an in ini y FCC s uc u al model wi h 12 a oms in he i s -shell coo dina ion30.
Pa icula ly, a change in he coo dina ion numbe was no obse ed heo e ical
calcula ion he o al coo dina ion numbe .
To al coo dina ion numbe o i s -shell was cons ained ollowing he heo e ical
calcula ion p oposes by D.T. T an e al. Who s udied he o al coo dina ion numbe as a
unc ion o he c ys al size. In addi ion, a change in NCu-Cu / NP -Cu was obse ed. The
DWFs o i s -shell Cu-P and Cu-Cu pa hs e eal he simila beha io showing highe
alues o he condi ioned sample measu emen . The mos signi ican ac is he
oscilla ion o he dis ance o P and Cu neighbo s. The i ing analysis concluded wo
di e en dis ances as a unc ion o he neighbo na u e. Bo h dis ances p esen di e en
beha io . Ini ially, nanopa icles uni cell p esen s an elonga ion o he majo i y Cu-Cu
bonds which a e educed o he heo e ical alues o well-de ined P Cu (1:3 mola
a io) i s -shell dis ance. The ini ial alues o he Cu-P bonds we e p ac ically he
same o ini ial Cu-Cu dis ance alues ( < 0.001 Å) which ag ees wi h he undamen al
concep o a FCC s uc u e; a=b=c. Howe e , du ing he condi ioning ea men , we
obse ed an inc emen o he Cu-P dis ance. Iden ical esul s we e ob ained om P L3-
edge EXAFS uc ion i ing. In he employed heo e ical s uc u e o designing he
i ing model, Cu a oms neighbo s a e loca ed in he equa o ial plane while P a oms
neighbo s a e loca ed in he axial plane. The e o e, he analysis concluded an equa o ial
S uc u al changes du ing he condi ioning ea men
63
comp ession wi h he Cu-Cu bonds dis ance dec emen and an axial elonga ion due o
he Cu-P dis ance inc emen .
Figu e 3.10. Schema ic illus a ion o dis ance modula ion on i s -shell coo dina ion.
Also, highe 2 alues a e he condi ioning ea men ( aking accoun he concomi an
nonze o esidual elas ic s ain ene gy) con i m he a oms ea angemen s om close
FCC s uc u e wi h a P 34Cu66 composi ion owa ds he e agonal dis o ion FCC
s uc u e wi h a P 27Cu73 composi ion and i is conclusi e o unde s anding he a omic
dynamic in he o de -diso de ansi ion33–35.
The highe -shell s uc u es do no suppo big in o ma ion due o he signal quali y. The
low coo dina ion numbe o he second and hi d shells is di ec ly ela ed o he ini e
size o he nanoalloy and he quali y o he signal32,36.
Chap e 4.
Su ace Cha ac e iza ion:
P obe Molecule Adso p ion
Es udio De Ca alizado es Basados En
Pla ino Pa a La Reacción De PROX:
In luencia De Los Depósi os De Ca bono

Su ace Cha ac e iza ion: P obe Molecule Adso p ion
71
4.1 In oduc ion
The knowledge o he ca alys su ace beha io is essen ial o he o al comp ehension o he
ma e ials. su ace may be conside a e such op-laye s o a oms wi h a la ge numbe o c ys al
de ec s as edges, e aces, s eps o co ne s o ally con olled by he solid s a e p ope ies. In
his sense, Fou ie ans o m in a ed spec oscopy (FTIR) e eals undamen al aspec abou
he chemical na u e o he su ace o abso bed species as well as s uc u al and s eng h bonds
in o ma ion1–3.
P obe molecule adso p ion by FTIR is one o he mos de eloped su ace cha ac e iza ion
me hods based in he s udy o he adso p ion complexes o med by he con ac be ween a
eac molecule and he su ace ca alys h ough which i is possible o s udy s ep by s ep he
possible pa hways in he mechanism eac ions as well as di e en p ope ies o he ca alys
such he basici y (p o on-accep ing) o acidi y o he ac i e si e, he kind o si e, he
adso p ion mode o he su ace concen a ion. The e a e se e al p obe molecules (ca bon
monoxide, ca bon dioxide, ni ogen oxide, py ole, alcohols among many o he s) and he
choice o one o hem depends o wha in o ma ion we wan o know as well as he si e
accessibili y o he spec al esponse.
T ying o unde s and he mechanism pa hway in he me hanol oxida ion eac ion, G. Busca e
al.4 ca ied ou he adso p ion o o maldehyde such model in e media e on di e en oxides.
They iden i ied and cha ac e ized di e en adso bed species om he ini ial o maldehyde as
a unc ion o empe a u e. Physiso bed HCHO species on su ace OH g oups we e ound a
low empe a u e while a oom empe a u e, dioxyme hylene species we e always obse ed.
Highe empe a u es in ol ed he disp opo iona ion o dioxyme hylene in o o ma e and
me hoxy g oups opening he di ec oxida ion way on e y s ongly oxidizing su aces by he
Cannizza o- ype mechanism.
Su ace Cha ac e iza ion: P obe Molecule Adso p ion
72
Ano he in e es ing wo k we e ca ied ou by E. Finocchio e al.5 who s udied he mechanism
o p opane and p opene oxida ion on MgC 2O4 by he small doses-adso p ion o di e en
p obe molecules based in C3, C2 and C1 oxygena es species. This pa icula ly sys em is
cha ac e ized because he solid is educed by eac ion gi ing ise oxidized o ganic species and
CO2. These au ho s obse ed di e en oxida ion pa hways o bo h molecules whe e p opene
oxida ion akes p e e en ial place by p e ious ac i a ion a C1. S ongly adso bed ac yla es
and ac olein species we e ound be o e o o al combus ion p ocess by he mal e ec s.
Howe e , abso bed ace one species we e obse ed as p e e en ial oxida ion p oduc o
p opane. Going on he oxida ion p ocess, ace one gi es o ma e and ace a e species which
bu n a highe empe a u es. The en i e obse ed su ace eac ions, join o he published da a
o simila ca aly ic sys ems, allowed hem o elucida e a gene al speci ic eac ion pa hway
o alkane and alkene ca aly ic oxida ion.
Fo he o he hand, acidi y and basici y p ope ies a e o ally ela ed wi h he ca aly ic
beha io o he solids. In his way, J.C. La alley6 epo ed he su ace basici y in wo o he
mos impo an ma e ials in he pe oleum chemis y, me al oxides and zeoli es, by di e en
p obe molecules adso p ion. Au ho concluded ha he bes p obe molecule o he
cha ac e iza ion o su ace base cen e s si es would be an H-dona ing HX molecule
elucida ing he basici y cha ac e o he si e by (H-X) shi .
A oiding s e ic limi a ions, A.M. Tu ek e al7 ca ied ou he acidic p ope ies s udy o
di e en alumina-suppo ed me al oxide ca alys s by he CO2 adso p ion as p obe molecule
ela ing he B öns ed acidi y wi h a obse ed band a low equency in he hyd oxyl egion
(3460-3490 cm-1) which is due o wa e molecules H-bonded o he B öns ed si es. Also,
di e en chemiso bed CO2 species we e iden i ied on he su ace o alumina ( igu e 4.1).
Su ace Cha ac e iza ion: P obe Molecule Adso p ion
73
Figu e 4.1. Obse ed FTIR bands (cm-1) upon CO2 adso p ion on pu e me al oxides.
Howe e , one o he mos used p obe molecule is ca bon monoxide which is he only known
molecule which has p e e en ial selec i i y o he basic si es by ca bonyls o ma ion6. Due o
he non- eac i e cha ac e adso p ion o he CO on he su ace ca alys , CO p obe molecule
p esen excellen cha ac e is ic o he s udy o he oxida ion and coo dina ion s a es o he
me al si es as well as o he s abili y and adso p ion mode o he o med ca bonyls
complexes3. Thus, C. Bine e al8 s udied he Lewis acid p ope ies o polyc ys alline ce ia in
oxidized and educed s a es by he e alua ion o he shi o gas phase (CO) alue. These
au ho s ca ied ou CO adso p ions a low empe a u e o a oiding he su ace ca bona ion
and, e e eed o he 2143 cm-1 alue o he CO gas phase equency, hey obse ed highe
shi s o highe wa enumbe (+26 cm-1) in he CO adso p ion on Ce3+ ions han o he Ce4+
Su ace Cha ac e iza ion: P obe Molecule Adso p ion
74
ion (+18 cm-1) which means ha Lewis acidi y o he ce ium ca ions dec eases in educe
s a es.
Mo eo e , se e al s udies ha e been epo ed abou CO adso p ion on P Cu based ca alys s,
objec solid o his manusc ip . Howe e , be o e he s udy o he in e me allic compounds
P Cu, i is necessa y a o al cha ac e iza ion o he monome al ca alys .
In he cases o coppe based ca alys , Cun+-CO su ace ca bonyls we e loca ed in a ange om
2240 o 1916 cm-1. Ca bonyls o med by Cu+ ions a e he mos s able species o Cun+-CO
complexes9. I was cha ac e ized by A. Dandeka e al.10 in a wide ange om 2160 o 2080
cm-1 du ing he CO adso p ion on suppo ed Cu ca alys , inding he ca bonyl on suppo ed
Cu on Al2O3 a ound 2130 cm-1 . Con e sely, Cu0-CO complexes o med by bond wi h he
coppe a oms and ca bonyls o Cu+2 ions a e uns able a oom empe a u e being de ec able by
CO adso p ion a low empe a u e (77 K)11. In addi ion, Lewis acid si es a e p esen on
alumina in e ahed al o oc ahed al coo dina ion9 showing ypical bands assigned o CO on
Al3+ a 2245-2215 cm-1 when samples a e ac i a ed a highe empe a u es( e ahed al
coo dina ion)12, bands a ound 2200 cm-1 when CO adso p ion is ca y ou unde equilib ium
condi ions and bands a ound 2170 cm-1 when CO is abso bed on Al3+ ca ions in oc ahed al
coo dina ion13.
CO adsop ion on suppo ed pla inum ca alys has been s udied by many au ho s due o he
impo ance o pla inum based ca alys in indus y. C.W. Olsen and R.I. Masel14 ca ied ou he
CO adso p ion on P (111) single c ys al inding wo di e en ca bonyl adso p ion mode on
pla inum si es; linea band a ound 2080 cm-1 and wo- old b idge bound CO a 1850 cm-1. A
shi o highe wa enumbe was obse ed by he CO co e age.
Fo he o he hand, CO adso p ion may p o ide in o ma ion abou me al coo dina ion,
geome y o adso p ion mode on he ac i e si e. H.J. Jänsch e al.15 s udied he su ace
Su ace Cha ac e iza ion: P obe Molecule Adso p ion
75
mig a ion o abso bed CO species on P (335) c ys al by elec onic exci a ion (elec on
s imula ed mig a ion). They dis inguished wo di e en adso p ion modes; abso bed CO on
s ep si es and Abso bed CO on e ace si es which hei ib a ional equencies o CO s e ch
mode a e clea ly sepa a ed a ound 25 cm-1. Then, J. Xu and J.T. Ya es J .16 assigned unde
low co e age condi ions band a ound 2072 cm-1 o CO adso bed on s ep si es. A e , since
co e age inc eased, a new band a 2100 cm-1 was obse ed due o he e minal-CO on he
e ace si es.
In he same way, P. Bazin e al.17 epo ed an exhaus i e s udy abou he CO adso p ion on
small pa icles o pla inum on ce ia suppo . Typical IR spec um a e he CO adso p ion on
suppo ed pla inum ca alys shows he linea ly adso bed CO band in a ange om 2090 cm-1
o 2000 cm-1 and he band associa ed wi h CO b idge be ween 1860 cm-1 and 1760 cm-1
( igu e 4.2a)18. Howe e , a e he CO adso p ion on educe P /CeO2 ca alys ( igu e 4.2b),
hey showed h ee di e en bands in he egion om 2100 cm-1 o 2000 cm-1 and a new one
band a 1937 cm-1, un ypical egion o he CO adso p ion bands. They p o ed he na u e o
hose bands by 12CO/13CO iso opic exchange, he mal analysis and CO adso p ion a low
empe a u e concluding; he band a highes wa e numbe (2096 cm-1) co espond o he CO
adso p ion on P + a oms, bands a ound 2054 cm-1 and 2010 cm-1 co espond wi h he linea ly
CO adso p ion on pla inum pa icles wi h di e en size while he new band a 1937 cm-1
appea s o he b idged CO adso p ion a he me al-suppo in e ace o Ce si es and small P
pa icles (<1.5 nm).

Su ace Cha ac e iza ion: P obe Molecule Adso p ion
76
Figu e 4.2. FTIR spec a a e CO adso p ion a oom empe a u e on non- educed P /CeO2 ca alys (a) and H2-
educed P /CeO2 ca alys a 673K (b).
Pla inum a oms wi h di e en pa icle size also could be loca ed in di e en en i onmen s.
A.Y. S akhee e al.19 s udied he elec onic s a e and localiza ion o suppo ed P a oms by
CO adso p ion. Those au ho s obse ed h ee bands a 2000, 2060 and 2075 cm-1 and hey
concluded ha he equency shi was due o he CO abso bed on pla inum si es wi h
di e en en i onmen . They explained how CO abso p ion on mo e accessible pla inum si es
loca ed nea o he exposu e su ace in ol e di e en deg ee o me al-suppo in e ac ion o
di e en pa icles shapes and hey ela ed his kind o si e wi h he band a 2075 cm-1. The
o he wo bands a 2060 and 2000 cm-1 we e assigned o me allic si e wi h lowe accessibili y
and also o CO adso bed on high dispe sed me allic pla inum a oms
Finally, he be e ca aly ic beha io o in e me allic P Cu compounds han monome al
ca alys has been demons a ed in he p e e en ial oxida ion o CO20. This ac and he
unknown ac i e si e na u e o one o he mos use ul comme cial ca alys o mobile de ices21
Su ace Cha ac e iza ion: P obe Molecule Adso p ion
77
does ha se e al au ho s ocus hei wo k in he sea ch o a sui able answe . Fo ins ance, T.
Koma su e al.22 showed he ela ionship o he me allic si e elec on densi y wi h he ca aly ic
ac i i y by he e alua ion o he (CO) shi a e he CO adso p ions on suppo ed P and Cu
ca alys as well as suppo ed in e me allic compound wi h di e en a omic a io (P 3Cu1 and
P 1Cu3) ( igu e 4.3). Also, F. Rome o-Sa ia e al.23 showed by ope ando FTIR s udy and CO
adso p ion on P Cu/Al2O3 ca alys , he e ec o o ganic deposi ( om he syn hesis p ocess)
in he elec on densi y o he ac i e si e and he e o e, he e ec in he ca aly ic ac i i y.
Figu e 4.3. FTIR spec a o adso bed CO on alumina suppo ed in e me allic compound P Cu as well as on bo h
suppo ed monome al ca alys .
Taking accoun his backg ound, in chap e 5 “Su ace Cha ac e iza ion: P obe molecule
adso p ion”, an exhaus i e s udy o he ac i e si e is ca ied ou by he abso p ion o CO and
NO p obe molecules a e he condi ioning ea men on he in e me allic compound P Cu (1:3
and 3:1 mola a io) as well as on he monome al ca alys s. Oxida ion s a e o he ac i e si e,
adso p ion modes, in e ac ion o he nanopa icles wi h he suppo , su ace species dynamic
and o he chemis y p ope ies we e desc ibed in he di e en sec ions.
Su ace Cha ac e iza ion: P obe Molecule Adso p ion
78
The mos impo an poin is he no modi ica ion o he ac i e si e na u e du ing he su ace
cleaning me hod. Also, i is necessa y he comple e unde s anding o he kind o he ac i e
si e, he su ace a ailabili y and he elec on densi y si e.
The main goal o his chap e is he s udy o he ac i e si e by he p obe molecule adso p ion
a e di e en condi ioning ea men s. Specially, CO adso p ions we e ca ied ou a e
hyd ogen ea men s (en i onmen based in he con en ional condi ioning ea men o P Cu
ca alys applied o mobile de ices) and a e he al e na i e su ace cleaning me hod based in
CO2 en i onmen on he P Cu in e me allic compound wi h di e en mola a io (P 3Cu1 and
P 1Cu3) as well as on he monome allic nanopa icles.
4.2 Su ace cha ac e iza ion o P / Al2O3
4.2.1 P / Al2O3
Fi s o all, unsuppo ed nanopa icles a e black so he ansmi ance is almos ze o and he
me al concen a ion is so high which supposes he sa u a ion o he signal. Fo a oiding his
p oblem, nanopa icles we e suppo ed on Al2O3 (226 m2/g) by a physic mix u e minimizing
he chemical in e ac ions me al-suppo . Mo eo e , due o he obse ed su ace composi ion
modi ica ion (chap e 2) and he elec on ans e du ing he condi ioning ea men in he
P Cu nanopa icles (chap e 3), i is necessa y he s udy o he monome allic nanopa icles
which should e eals he ole o each compound. Thus, se e al CO adso p ions on P / Al2O3
expe imen s we e ca ied ou a e H2 ea men and CO2 ea men .
Su ace Cha ac e iza ion: P obe Molecule Adso p ion
79
Figu e 4.4. Backg ound spec a (a . ) o he esh P / Al2O3 sample (yellow colo ) and a e CO2 ea men
( ed colo ) and H2 ea men (blue colo ). The inse shows a magni ica ion o a ound band a ound 2055cm-1
a e condi ioning ea men s.
The backg ound spec a o he P / Al2O3 a e shown in Figu e 4.4. The p esence o esidual
ca bonaceous species and adso bed –OH and –CHx g oups we e obse ed on he esh ca alys
su ace. Spec a a e wo p oposed ea men s showed simila su ace g oups. Specially, i
d aws a en ion he p esence o –CHx g oups in he egion be ween 2900 cm-1 and 3000 cm-1
as well as he p esence a cha ac e is ic band a 2055 cm-1 o abso bed ca bonyls species on he
pla inum nanopa icles su ace be o e s a he CO adso p ion24. I could be due o he ca bons
deposi decomposi ion du ing he simula ed condi ioning ea men in he in si u cell. This
ea men is ca ied ou in s a ic condi ions and employed en i onmen only can be emo ed
a ound 200°C o a oiding possible e ec s in he oxida ion s a es. A his empe a u e,
esidual ca bon species a e eabso bed on he pla inum su ace25.
4.2.2 CO adso p ion on P / Al2O3
Then, CO adso p ions a e in si u ea men s we e ca ied ou . Spec a acqui ed du ing he
CO adso p ion a e H2 and CO2 ea men showed he same g oups o bands. The e o e, bo h
Su ace Cha ac e iza ion: P obe Molecule Adso p ion
86
Figu e 4.9. Schema ic simula ion o he CO adso p ion on P / Al2O3 a e H2 ea men . CO dissocia ion is
a oided by ca bon deposi s. Black ca bon a oms sham ca bons deposi s om he syn hesis s ep and blue ca bons
a oms shams ca bons deposi s om he pa ial CO dissocia ion.
Du ing he CO adso p ion a e CO2 ea men , pla inum is o ally a ailabili y. CO is
dissocia ed by P a oms and he inc emen o he CO concen a ion means an inc emen o
CO2 gas phase band cause by CO oxida ion. The small dec emen o CO2 gas phase band
in ensi y could be caused by he ca bon deposi s om he CO dissocia ion bu due o he high
su ace eac i i y ( o al a ailabili y o pla inum ac i e si e) he CO2 gas phase is always
p esen , including unde CO sa u a ion condi ions.
4.2.3 Oxygen addic ion on P / Al2O3
Fo he o he hand, he subsequen oxygen in oduc ion in o he cell a e he p e- ea men
should e eal he possible ca bon deposi p esence by di ec oxida ion. Thus, oxygen small
doses addic ion we e ca ied ou on he non-condi ioned P / Al2O3 ( esh ca alys ) and a e
H2 and CO2 condi ioning ea men s. The main goal o his s udy was he e alua ion o he
amoun o su ace ca bon deposi s in he h ee p oposed si ua ion and he e ec s o adso bed
molecula oxygen om he CO dissocia ion on he pla inum oxida ion s a e. Fi s , he
e olu ion o he CO2 bands was ollowed du ing he oxygen small doses addic ion ( igu e
4.10). Since added oxygen amoun inc eases, CO2 p oduc ion inc eases by di ec gasi ica ion
o su ace ca bon deposi (Eq.(8)).
(8) C* + O2 (g) → CO2 (g) + *
In he case o non-condi ioned ca alys and a e H2 ea men , he e is a ema kable su ace
ca bon amoun . Condi ions du ing he oxygen addic ion (exposu e ime, empe a u e, oxygen
amoun , e c.) a e no enough o he o al su ace ca bon emo ing by gasi ica ion p ocess, so
CO2 bands a e p esen o all he expe imen . In he addic ion o oxygen small doses on

Su ace Cha ac e iza ion: P obe Molecule Adso p ion
87
P / Al2O3 a e CO2 ea men , su ace ca bon amoun is almos ze o. The e o e, since added
oxygen amoun inc eases, he low su ace ca bon amoun dec eases by di ec ly gasi ica ion
and he CO2 bands in ensi ies becoming ze o.
Rela i e o he me allic si e, abso bed CO om he pa ial ca bon gasi ica ion and CO2
dissocia ion was ound du ing he oxygen addi ion a e H2 and CO2 ea men . Figu e 5.7.b
shows bands a 2064, 2130 and 2174 cm-1 assigned o linea ly abso bed CO on me allic
pla inum nanopa icles, CO abso bed on pla inum a oms wi h low elec on densi y (
a oms) and abso bed CO on (Al+3)Oc . Bands obse ed on he P / Al2O3 ca alys a e CO2
condi ioning ea men p esen lowe in ensi y due o he less su ace ca bon deposi p esence.
The e o e, e ec s on he oxida ion s a e by he oxygen exposu e a oom empe a u e we e no
obse ed.
Figu e 4.10. a) E olu ion o he CO2 band a ea du ing he small doses oxygen addic ion on non-ac i a ed
P / Al2O3 (yellow colo ) and on P / Al2O3 a e H2 ea men (blue colo ) and CO2 ea men ( ed colo ). b)
Abso bed CO a e oxygen addic ion on P / Al2O3 p e ea ed unde H2 a mosphe e (blue colo ) and CO2
a mosphe e ( ed colo ).
Su ace Cha ac e iza ion: P obe Molecule Adso p ion
88
4.3 Su ace cha ac e iza ion o Cu/ Al2O3
4.3.1 Cu/ Al2O3
Figu e 4.11 shows he backg ound spec a o Cu/ Al2O3 a e H2 ea men and CO2
ea men . A lowe wa enumbe , ini ial bands a 1578, 1465 and 1264 cm-1 we e obse ed.
Da ydo 36 and B.A. Sex on37 assigned hose bands by ace ic adso p ion on di e en oxides o
he υas(COO), υs(COO) and υ(C-C) ib a ional modes cha ac e is ic o abso bed ace a es
species. This species can be disc imina e by b idge ace a es species and biden a e ace a e
species. υ(COO) depends o he (OCO) angle being om 171 o 523 cm-1 o b idge ace a e
species and be ween 65 and 115 cm-1 o biden a e ace a e species. υ(COO) o he ound
bands a 1578 cm-1 (υas(COO),) and 1465 cm-1 (υa(COO)) is 113 cm-1 so, biden a e ace a e
species a e p esen on he su ace o coppe ca alys .
Con a y o P / Al2O3, CO adso bed on he me allic si es a e bo h di e en ea men s was
no ound. Ace a es species p esence in ol es ib a ional modes on he –CHx egion.
Di e en bands we e obse ed a 2842 and 2914 cm-1 cha ac e is ic o he υs(CH3) and
υas(CH3). Also, bands a 2869 and 2959 cm-1 co espond o υ(CH) ib a ional modes.
Su ace Cha ac e iza ion: P obe Molecule Adso p ion
89
Figu e 4.11. Backg ound spec a o Cu/ -Al2O3 a e H2 condi ioning ea men (blue colo ) and CO2
condi ioning ea men ( ed colo ).
Finally, ib a ional modes co espond o –OH g oup we e obse ed. I can be dis inguished
ou di e en bands a 3580, 3678, 3730 and 3757 cm-1. Mo e a e al.12,38 desc ibed he OH
s e ching spec a o alumina and hey assigned band a 3757 cm-1 wi h e minal OH g oups
coo dina ed on o su ace e ahed al aluminium cen e s. Mo eo e , Digne e al.28 ca ied ou
a simula ion o su ace OH s e ching en i onmen by DFT s udy and hose au ho s desc ibed
he coo dina ion o abo e band a 3757 cm-1 such OH g oups linked o single aluminium a om
which is su ounded by six di e en oxygen a oms. Band a 3730 cm-1 was assigned by
Mo e a e al. 12,38 o OH g oups bib idged ac oss Al-Al pai while Digne e al.28 calcula ions
ela ed his band wi h e minal OH g oups bonded o single aluminium a om which is
su ounded by i e oxygen a oms. Con a y o Mo e a e al.12,38, hose au ho s and Busca e
al.39 ela ed he band a 3678 cm-1 o OH g oups b idge be ween wo aluminium a oms which
a e su ounded by i e oxygen a oms. Las , band a 3580 cm-1 is ela ed wi h OH g oup
ib idged o aluminium a oms su ounded by six oxygen a oms.
Su ace Cha ac e iza ion: P obe Molecule Adso p ion
90
4.3.2 CO adso p ion on Cu/ Al2O3
Compa ison o di e ence FTIR spec a a e CO adso p ion on Cu/ Al2O3 is showed in
igu e 4.12.
Figu e 4.12. Di e ence FTIR spec a a e CO adso p ion on Cu/ Al2O3 p e ea ed unde H2 a mosphe e (blue
colo ) and CO2 a mosphe e ( ed colo ). 0.26µmol o CO added in bo h cases.
I is clea e idence a highe abso bed CO band in ensi y on he coppe si e as well as in he –
OH egion when ca alys is ea ed unde CO2 en i onmen . Figu e 4.13 shows he di e ence
FTIR spec a eco ded du ing he CO adso p ion on Cu/ Al2O3 a e H2 and CO2 ea men .
In e es ingly in bo h cases, a main band can be obse ed a 2123 cm-1 wi h a shoulde o lowe
wa enumbe a 2098 cm-1. In addi ion, a weak band o 2165 cm-1 can be obse ed. I means
ha he na u e o p e- ea men does no a ec he oxida ion s a e o he coppe pa icles.
Howe e , his band is shape when sample is ea ed unde H2 a mosphe e. Di e en
possibili ies could be p oposed o he o igin o such o Cu si es. K.I. Hadjii ano and G.N.
Vayssil o 9 desc ibed equencies o he su ace ca bonyls abso bed on he coppe a oms as a
Su ace Cha ac e iza ion: P obe Molecule Adso p ion
91
unc ion o he coppe oxida ion s a e concluding ha he cha ac e is ic band o linea ly
ca bonyls abso bed on Cu2+ (Cu2+-CO) is loca ed be ween 2220 and 2150 cm-1, band o
ca bonyls abso bed on Cu+ (Cu+-CO) is loca ed be ween 2160 and 2080 cm-1 while ca bonyls
abso bed on me allic coppe (Cu0-CO) show a weak band lowe han 2130 cm-1.
Figu e 4.13. Di e ence FTIR spec a du ing he CO adso p ion on Cu/Al2O3 a e CO2 ea men (a) and H2
ea men (b).
Fo he o he hand, Zecchina e al.40 ca ied ou a CO adso p ion on silica suppo ed coppe
ca alys a e p og essi e educ ion s ep unde H2 en i onmen a di e en empe a u es.
When Cu/SiO2 was educed a 400ºC, hey obse ed wo bands; a weak band a 2163 cm-1 and
a sha pe band a 2136 cm-1. They concluded ha bo h bands a e due o CO abso bed on small
Cu+ a oms on ex ended aces and edges and s eps espec i ely. Also, Hadjii ano e al.9
p oposed he band a 2165 cm-1 due o ca bonyls abso bed on Cu2+ species. Mo eo e , when
educ ion empe a u e was inc eased du ing he CO adso p ion on Cu/SiO2, a new shoulde
a ound 2100 cm-1 was obse ed and hey assigned his band o CO abso bed on me allic
coppe o CO abso bed on a Cu- ich non s oichiome ic Cu2O phase. Thus, he CO abso p ion
on Cu2+ species, ca bonyls abso bed on small pa icles o Cu+ (p obably loca ed in he me al-
suppo in e ace) and CO abso p ion on me allic coppe could be assigned o he ound band

Su ace Cha ac e iza ion: P obe Molecule Adso p ion
92
a 2165, 2122 and 2098 cm-1 in ag eemen wi h Zecchina e al.40 and Hadjii ano 9
conclusions. Howe e , he p esence o Cu2+ species canno be possible a e he educe H2
ea men . I is means ha band a 2165 cm-1 could be due o ca bonyls abso bed on Cu+1
species o CO abso bed on he Al3+ ca ions om he suppo in oc ahed al coo dina ion
((Al+3-CO)oc ). No e ha e ahed al si e on alumina a e blocked by coppe pa icles a oiding
he CO adso p ion. Thus, he a ibu ion o bands a 2122 cm-1 o Cu+1 species a e a educe
ea men could be explained wi h suppo -me al in e ac ions by he –OH g oups e alua ion.
Figu e 4.14 ν(OH) ib a ional modes o he OH g oups p esen on Cu/Al2O3 du ing he CO adso p ion a e CO2
ea men (a) and H2 ea men (b).
Figu e 4.14 ep esen s he OH ib a ion egion du ing he CO adso p ion a e CO2 ea men
(a) and H2 ea men . Bands a ound 3622, 3650, 3684 and 3755 cm-1 we e obse ed in bo h
cases. Those bands we e assigned o e minal OH g oups coo dina ed on o su ace e ahed al
aluminium cen e s (3755 cm-1)38, o OH g oups linked o e ahed al and oc ahed al Al+3
ca ions (3684 cm-1)41 and o he ν(OH) modes o he OH g oups p esen in he newly o med
mono (3650 cm-1) and biden a e hyd ogen ca bona es (3620 cm-1)42. Quan i a i ely, lowe
in ensi y o he bands assigned o he OH ib a ional modes was obse ed a e H2 ea men ,
being he in ensi y o he me allic si es ( om 1950 o 2200 cm-1) a ec ed in he same way.
Su ace Cha ac e iza ion: P obe Molecule Adso p ion
93
The simila beha io o bo h g oups o band is ela ed wi h he s eng h o he in e ac ion
suppo -me al, i.e. coppe -alumina in e ac ion is s onge a e H2 ea men . Acco ding wi h
he conclusions o K. Bechoux e al.41 who s udied CO adso p ions on Ag/Al2O3 a e
educing and oxidizing p e ea men s, alumina hyd oxyls g oups p esen on he su ace o
Cu/Al2O3 a e he CO2 ea men emain s able in he in e ace o coppe nanopa icles –
alumina suppo , while a e he H2 ea men , coppe a oms in e ac wi h he close OH
g oups (neighbo ing basic oxygen) dec easing he a ailable coppe si es o he CO
adso p ion. Also, neighbo s basic oxygen ans e elec on densi y o he coppe a oms
allowing he Cu+-CO complexes and i s cha ac e is ic band a 2122 cm-1. Despi e he expec ed
me allic si e o coppe nanopa icles, he p esence o Cu+1 species could be ela ed o he
elec ophilic beha io o coppe a oms in he p esence o CO molecules p oposed by Koma su
e al.22 who concluded ha Cu a oms abso b possible oxygen a oms om CO dissocia ion
o igina ing species.
In summa y, obse ed bands a 2098, 2122 and 2163 cm-1 a e bo h ea men s a e ela ed
wi h he CO adso p ion on me allic coppe species, CO abso bed on Cu+1 species and
abso bed CO on Al3+ ca ions wi h oc ahed al coo dina ion ((Al+3-CO)oc ). Mo eo e , an
impo an de ail is he no o ma ion o CO2 bands du ing he CO adso p ion on Cu/ Al2O3.
As expec ed, he CO adso p ion a oom empe a u e a e H2 and CO2 ea men s on
Cu/ Al2O3 exhibi di e en bands in he egion be ween 1100 and 1800 cm-1. Fi s , du ing he
CO adso p ion a e H2 ea men , bands a 1229, 1264, 1374, 1396, 1432, 1468, 1579, 1619
and 1657 cm-1 we e obse ed ( igu e 4.15).
Su ace Cha ac e iza ion: P obe Molecule Adso p ion
94
Figu e 4.15. FTIR spec a du ing CO adso p ion on Cu/Al2O3 a e H2 ea men .
S ong ca bona es bands we e obse ed du ing he CO adso p ion on Cu/Al2O3 a e H2
ea men a 1657, 1432 and 1229 cm-1. The assignmen o he bands is no simple due o he
di e en s uc u es showed by ca bona es. The obse ed bands co espond o hyd ogen-
ca bona es species; νas(COO) a 1657 cm-1, νs(COO) a 1432 cm-1 and (OH) a 1229 cm-1.
Howe e , di e en ca bona es species on he su ace alumina should be expec ed. Weak
bands a 1579, 1468 and 1264 cm-1 co espond o υas(COO), υs(COO) and υ(C-C) ib a ional
modes o abso bed ace a es species and bands a 1374, 1396 and 1579 cm-1 cha ac e is ic o
o ma es species we e ound36. Howe e , he in ensi y o he seconda y o med ca bona es
species bands a e ex emely weak e en no showing he CH s e ching ib a ional mode.
Thus, only hyd ogen-ca bona es species we e conside a e o he su ace analysis.
K. Fö inge e al.43 s udied he possible pa hways mechanism o ca bona e o ma ions on
Pd/Al2O3 and hey concluded ha he o ma ion o hyd ogen-ca bona es akes place ia
“wa e gas shi ” eac ion be ween CO and alumina hyd oxyl g oups ollowed by he eac ion
Su ace Cha ac e iza ion: P obe Molecule Adso p ion
95
o he o med CO2 wi h o he OH g oups. This ac and he s ong in e ac ion be ween coppe
a oms and hyd oxyl g oups could be explains he absence o wa e ( igu e 4.14b).
Fo he o he hand, igu e 4.16 shows he ca bona es egion o Cu/Al2O3 du ing he CO
adso p ion a e CO2 ea men . I clea e iden he inc emen o he hyd ogen-ca bona es
bands a 1657 cm-1 (νas(COO)), 1430 cm-1 (νs(COO)) and 1228 cm-1 ( (OH)) wi h inc easing
CO amoun s.
Figu e 4.16. FTIR spec a du ing he CO adso p ion on Cu/Al2O3 a e CO2 ea men .
In his case he e is a ema kable species ans o ma ion. Fi s , an isosbes ic poin a 1465 cm-
1 was obse ed. This equency co espond o he o abso bed ace a es species which a e
dec easing wi h he CO adso p ion. Band co espond o υas(COO) o ace a e species is no
shown due o a change o slope wi h he o ma ion o o he species. Mo eo e , acco ding o
Mo e a e al.44, he p esence o he isosbes ic poin a 1465 cm-1 e idence he p esence o
di e en hyd ogen-ca bona es du ing he CO adso p ion and he ans o ma ion o he su ace
species om hyd ogen-ca bona es B2, which a e mainly o med by he in e ac ion o CO2
Su ace Cha ac e iza ion: P obe Molecule Adso p ion
102
Figu e 4.22. Di e ence FTIR spec a o CO adso p ion a oom empe a u e on P / Al2O3 (o ange colo ) and
CO adso p ion on P 3Cu1/ Al2O3 a e H2 ea men (blue colo ) and CO2 ea men ( ed colo ). Bands wi h solid
lines co espond o species on P 3Cu1/ Al2O3 and bands wi h dash lines co espond o species on P 3Cu1/ Al2O3.
A e he CO adso p ion on P / Al2O3 p e ea ed unde bo h ea men s, bands a 1684, 1578,
1378 and 1290 cm-1 assigned o ac yla es species we e obse ed (see igu e 4.6). Howe e ,
he addic ion o small amoun o coppe supposes di e en su aces species. A e he CO
adso p ion on P 3Cu1/ Al2O3 p e ea ed unde H2 and CO2 a mosphe e, bands a 1656, 1432
and 1229 cm-1 assigned o hyd ogen-ca bona es we e obse ed. Howe e , when sample is
p e ea ed unde H2 a mosphe e, he dec emen o bands a 1578 and 1460 cm-1 cha ac e is ic
o abso bed ace a es species is showed. Thus, coppe species in P Cu alloy (3:1 mola a io)
induce he su ace hyd oca bons oxida ion. Ini ial ac yla es species o med by pla inum a oms
a e oxidized o ace a es species50. Wi h he inc emen o oxida ion deg ee, ace a es species a e
oxidized o CO2 and H2O which in ol es an enhanced o he si es a ailabili y. Finally, CO2
and H2O o m hyd ogen-ca bona es ( igu e 4.23)50.

Su ace Cha ac e iza ion: P obe Molecule Adso p ion
103
Figu e 4.23. Mechanism o hyd oca bon oxida ion on he P 3Cu1/ Al2O3 su ace.
The appea ance o he dec easing bands o ace a es species in samples p e ea ed unde
hyd ogen en i onmen means a lowe eac ion a es o he hyd oca bons oxida ion. Small
CO2 p oduc ion was obse ed du ing he CO adso p ion on P 3Cu1/Al2O3 a e H2 ea men .
Fo he o he hand, when sample is p e ea ed unde CO2 en i onmen , only he inal p oduc
is app eciable.
4.4.2 CO adso p ion on P 1Cu3/ Al2O3: The ole o Pla inum.
To elucida e he ole o pla inum in he in e me allic compound P Cu, CO adso p ion on
P 1Cu3/Al2O3 a e CO2 and H2 p e ea men we e ca ied ou (Figu e 4.24).
Su ace Cha ac e iza ion: P obe Molecule Adso p ion
104
Figu e 4.24. Di e ence spec a o CO adso p ion on P 1Cu3/Al2O3 a e CO2 ea men ( ed colo ) and H2
ea men (blue colo ).
Du ing he CO adso p ion a e bo h p e ea men s, bands cha ac e is ic o abso bed ca bonyls
on coppe species appea a he same equency, 2098 and 2122 cm-1. Conside ing he Cu-
ich su ace composi ion be ween 63 and 83% o coppe species calcula ed by APXPS o he
unsuppo ed P 1Cu3 nanopa icles (Figu e 3.5, chap e 3), he su ace o P 1Cu3/Al2O3 ca alys
is ex em ly simila o he Cu/Al2O3 su ace and he obse ed bands a 2098 and 2122 cm-1
could be ela ed o ca bonyls abso bed on me allic coppe species and Cu+ species
espec i ily. The di e en in ens ies is due o he su ace claneaning me hod e ec i i y.
P 1Cu3/Al2O3 su ace is mo e a ailabili y o he ca bonyls abdso ion a e CO2 ea men s.
Mo eo e , as in he case o CO adso p ion on Cu/Al2O3 (sec ion 4.3.2), coppe a oms p esen
highe in e ac ion wi h he alumina OH g oups which supposes a less a ailabil y si es o he
CO adso p ion. Finally, band a 2172 cm-1 was assigned o ca bonyls abso bed o Al+3 ca ions
in oc ahed al coo dina ion ((Al+3-CO)oc ).
A compa ison o he FTIR spec a eco ded in he 1000-1800 spec al egion o Cu/Al2O3 and
P 1Cu3/Al2O3 ca alys is shown in igu e 4.25. In e me allic compound suppo ed on alumina
p esen simila su ace species a e he p e ea men in CO2 and H2 en i onmen . The e is a
clea hyd oca bon oxida ion p ocess du ing he CO adso p ion in bo h ca alys . Bands a 1229,
1432 and 1657 cm-1 cha ac e is ic o hyd ogen ca bona es species a e clea ly inc esing while
bands a 1470 and 1580 cm-1 cha ac e is ic o abso bed ace a e species a e dec easing. In he
case o CO2 p e ea men , binden a e ca bona es we e no obse ed on he P 1Cu3/Al2O3
su ace and, con a y o he CO adso p ion on Cu/Al2O3, he dec emen o he band
co espond o he υas(COO) ib a ional mode a 1580 cm-1 is e iden .
Su ace Cha ac e iza ion: P obe Molecule Adso p ion
105
Finally, while CO2 p oduc ion was obse ed du ing he CO adso p ion on P 3Cu1/Al2O3 a e
H2 ea men , in his case, weak bands cha ac e is ic o CO2 gas phase was obse ed du ing
he CO adso p ion on he P 1Cu3/Al2O3 a e CO2 ea men .
The e o e, acco ding wi h he a obe compa ion, P 1Cu3/Al2O3 a e bo h ea men shows a
low eac ion a e o he su ace hyd oca bons oxyda ion espec o he P Cu alloy 3:1 mola
a io. The ace a es species oxida ion o CO2, clea ly e idenced wi h he dec emen o bands a
1470 and 1580 cm-1, and he no CO2 oxida ion o hyd ogen-ca bona es species could be
explain he highe CO con e sions and selec i i y o CO2 o he in e me allic P Cu 1:3 mola
a io based ca alys du ing he p e e en ial oxida ion o CO23,51.
Figu e 4.25. Di e ence FTIR spec a compa ison be ween he CO adso p ion on Cu/Al2O3 (o ange colo ) and
P 1Cu3/Al2O3 a e CO2 ea men ( ed colo ) and H2 ea men (blue colo ).
4.5. Conclusions
Th oughou his chap e , a comple e su ace cha ac e iza ion by p obe molecule abso p ion o
nanopa icles suppo ed on alumina has been shown. The ini ial monomen al ca alys s
cha ac e iza ion e ealed he me allic cha ac e si e o he monome al pla inum ca alys as
well as he simul anei y p esence o Cu+1 and me allic coppe species on he su ace o coppe
Su ace Cha ac e iza ion: P obe Molecule Adso p ion
106
suppo ed on alumina. Di e en su ace species we e obse ed as a unc ion o he ac i e si e
na u e wi hou in luence o he condi ioning ea men .
The e iciency o he condi ioning ea men s based in CO2 and H2 a mosphe es was p obed
by he CO and O2 adso p ion showing an enhance o he a ailabili y su ace a e CO2
ea men s. Mo eo e , he in luence o me al-suppo in e ac ions on he ac i e si e was
e alua ed by he co ela ions o he alumina OH g oups and ca bonyls abso bed on he ac i e
si e. Also, oxida ion s a e o monome al coppe ca alys was con i med by NO p obe molecule
adso p ion.
The ole o bo h me als in he in e me allic compound P Cu was s udied by CO adso p ion on
suppo ed P Cu nanopa icles alloy wi h di e en mola a ios on alumina. The su ace
hyd oca bons oxida ion by coppe e ec s has been concluded showing di e en eac ion a e
as a unc ion o he condi ioning ea men . Fo he o he hand, he main ole o pla inum is
he CO dissocia ion which allows he CO2 o ma ion by di e en pa hway mechanism.
4.6 Associa ed con en
P ocedu e ca ied ou o he p obe molecule adso p ion was always he same. Fi s , sample is
p essed in pelle o m o 15-20 mg and 2 cm2 o a ea (spec a a e no malized by he a ea and
weigh ). A e , 5 To condi ioning en i onmen is in oduced in he acuum sys em a oom
empe a u e. In his poin , condi ioning ea men simula ion s a s. Sample is hea ing a 350ºC
o 2 hou s (hea ing a e o 10ºC/min). Then, sample is cooling down wi hou cooling a e
ollow by gas e acua ion a 200ºC empe a u e ying o enhance he e acua ion e iciency.
Finally, p obe molecule adso p ion s a s a oom empe a u e when he o al acuum in he
cell is almos 10-6 mba . P obe molecule doses o 0.1 To a e added un il su ace sa u a ion.
Su ace Cha ac e iza ion: P obe Molecule Adso p ion
107
Figu e 4.26. Schema ic p obe molecule adso p ion p o ocol.
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Chap e 5.
Model Ca alys Cha ac e iza ion
Unde Reac ion Condi ions
Es udio De Ca alizado es Basados En
Pla ino Pa a La Reacción De PROX:
In luencia De Los Depósi os De Ca bono
Model Ca alys cha ac e iza ion unde eac ion condi ions
118
Second ca aly ic cycle p esen s highe CO con e sion alues om all he eac ion
empe a u e ange. Rep oducibili y s udy con i ms a change in he ca aly ic beha io
a ound 200ºC showed by a modi ica ion o he slope in he CO con e sion line
e olu ion. This change is also obse ed in he second cycle. Selec i i y owa d CO2
o ma ion shows a dec emen wi h he empe a u e inc emen . I mus be conside ed ha
a e H2 p e ea men , ca bon deposi s a e p esen on he nanopa icles su ace (see
sec ion 2.2.2, chap e 2) while a e he su ace cleaning me hod, nanopa icles su ace
a e comple ely ee o ca bonaceous es s. Conside ing ha a e he su ace cleaning
me hod, changes in he elec onic su ace and he geome ic s uc u e we e no obse ed
e e eed o he unsuppo ed nanopa icles p e ea ed unde H2-a mosphe e (chap e 2) ,
he di e en CO con e sion could be ela ed wi h he p esence o absence o ca bon
deposi s on he nanopa icles su aces. The e o e, ee-ca bon deposi s su aces in ol e
lowe CO con e sion while somehow, su ace ca bon deposi s p esence a e ela ed wi h
highe CO con e sion alues.
Howe e , he applica ion o his sys em in mobile de ices supposes he
ac i a ion o he ca alys s unde he eac ion a mosphe e. Fo his eason, ca aly ic
ac i i y o unsuppo ed P Cu3 nanopa icles p e ea ed unde eac ion mix u e
en i onmen a e he su ace cleaning me hod applica ion was e alua ed ( igu e 5.4).

Model Ca alys cha ac e iza ion unde eac ion condi ions
119
Figu e 5.4. Ca aly ic ac i i y o he P Cu3 nanopa icles as a unc ion o eac ion empe a u e.
Nanopa icles we e condi ioned unde eac ion mix u e en i onmen . (a) Reac ion low composi ion: 50%
H2, 10% CO2, 1% O2, 1% CO and N2 balance. (b) Reac ion low composi ion: 50% H2, 10% CO2, 10%
H2O, 1% O2, 1% CO and N2 balance.
Figu e 5.4a shows he ca aly ic ac i i y o unsuppo ed nanopa icles p e ea ed
unde eac ion mix u e en i onmen a 350ºC o 2 hou s in d y condi ions. I is
app eciable a simila ca aly ic beha io ha nanopa icles p e ea ed unde H2- low
( igu e 5.3a). In his case, a maximum o 56% o CO con e sion was obse ed in he
i s cycle while he second cycle supposed an inc emen o he CO con e sion a lowe
empe a u e wi h a maximum CO con e sion o 61% a 210ºC. In bo h cycles, CO
con e sion is con olled by he modynamic equilib ium a e he maximum alue. In all
he cases, selec i i y alues dec ease wi h he inc emen o eac ion empe a u e.
Howe e , when 10% H2O was added o he main low in he condi ioning
ea men , unsuppo ed P Cu3 nanopa icles showed a o ally di e en ca aly ic beha io
( igu e 5.4b). The p esence o wa e in he eac ion mix u e in ol es lowe CO
con e sion wi h linea ly posi i e end wi h he inc emen o eac ion empe a u e.
Simila o he samples condi ioned unde CO2 a mosphe e, he e is a change o slope a
200ºC in he CO con e sion and CO con e sion a e he second cycle p esen s highe
alues.
Model Ca alys cha ac e iza ion unde eac ion condi ions
120
Figu e 5.5. APXPS C1s spec a om unsuppo ed P Cu3 nanopa icles acqui ed du ing he eac ion s ep
a 200ºC in di e en eac ion mix u e composi ion; 50% H2, 10% CO2, 1% O2, 1% CO, 10% H2O and N2
balance (blue line) and same composi ion wi hou wa e (g een line). The IMFP o C1s pho oelec on was
5 Å.
A simula ion o he condi ioning ea men and eac ion s ep unde bo h di e en
eed s eams (d y and we ) o he unsuppo ed P Cu3 nanopa icles was ca ied ou by
APXPS expe imen s. Figu e 5.5 shows he C1s spec a acqui ed du ing he eac ion s ep
a 200ºC. G een line shows he e olu ion o C1s signal om nanopa icles su ace
du ing he eac ion s ep in absence o wa e . I is app eciable a ema kable signal wi h a
main compound a 284.6 eV co espond o C-C species om he syn hesis s ep.
Howe e , he addi ion o wa e supposed a d ama ically dec emen o he C1s signal.
This ac could explain he obse ed di e en ca aly ic beha io which showed highe
CO con e sion o ca bon-pollu ed su aces and i could accep he hypo hesis p oposed
by Rome o-Sa ia e al.13 based in he posi i e ole o ca bon in he p e e en ial
oxida ion o CO.
Model Ca alys cha ac e iza ion unde eac ion condi ions
121
In o de o con i m he posi i e ole o ca bon in he con en ional P xCuy
ca alys o P Ox eac ion, ca aly ic ac i i y o wo di e en eed s eams o
nanopa icles suppo ed on Al2O3 was e alua ed. As i was concluded be o e, d y
eac ion en i onmen in ol es he p esence o ca bon deposi s on he nanopa icles
su ace while he p esence o wa e in he eal eac ion mix u e low means almos he
o ally emo ing o su ace ca bon o e laye s.
Figu e 5.6. P Ox eac ion pe o mance compa ison o P Cu3/ Al2O3 unde d y eed s eam (a) and we
eed s eam (10% H2O) (b).
Figu e 5.6 shows he P Cu3/ Al2O3 ca aly ic ac i i y o d y and we eed
s eams. As obse ed in igu e 5.6a o d y eac ion condi ions, CO con e sions in bo h
as ed cycles p esen maximum CO con e sion alues a ound 80-85% a 150ºC being
limi ed om his poin by he he modynamic equilib ium. In he case o we eed
s eams, P Cu3/ Al2O3 p esen s simila global ca aly ic beha io showing lowe CO
con e sion a low empe a u es in he i s cycle. P obably, he low CO con e sion
alues a low empe a u e o we eac ion condi ions co espond wi h ee-su ace o
ca bon deposi s on he nanopa icles and suppo . Howe e , he p esence o suppo
could be a o ing he deposi o ca bon es s on he alumina su ace du ing he eac ion
Model Ca alys cha ac e iza ion unde eac ion condi ions
122
which in ol es a change in he ca aly ic p ope ies owa d he obse ed ca aly ic
beha io unde d y condi ions (see sec ion 4.4.2, chap e 4).
Doing a compa ison o he ca aly ic ac i i ies o P Cu3/ Al2O3 and unsuppo ed
P Cu3 nanopa icles can be obse ed highe CO con e sion alues o he suppo ed
nanopa icles. The s ong in luence o he suppo on su ace ea angemen s o
bime allic nanopa icles was epo ed by Di ins e al.14. Alumina suppo can p o ide
new ac i e si es and i can be a ec ing o he physical and chemical p ope ies o
nanopa icles. In his way, hanks o he p esen o Al2O3 suppo , CO con e sion
eaches he maximum alue and he equilib ium alues a lowe empe a u e han
unsuppo ed nanopa icles. In all he cases, selec i i y owa d CO2 o ma ion shows he
same linea ly end o lowe alues wi h he inc emen o eac ion empe a u e.
Howe e , he use o Al2O3 allows side eac ions which induce o loss o 25% o
selec i i y.
5.3 Su ace dynamic du ing P Ox eac ion
Come back o he main goal o his manusc ip , a e he s udy o he ole o
su ace ca bon deposi s, ano he possible answe o he un ypical ca aly ic beha io o
P xCuy nanopa icles based ca alys s o P Ox eac ion could be he su ace dynamic o
ea angemen s o P Cu nanopa icles unde wo king condi ions. F. Tao e al.5 showed
how some s uc u es and ac i e phases only exis unde eac ion condi ions. In his way,
su ace in si u cha ac e iza ion is essen ial o iden i y he ac i e si es a wo k as well as
he es uc u ing phenomena as a unc ion o he su ounding en i onmen and
empe a u e. The e o e, a e he su ace cleaning me hod (exchange capping ligand
me hod and CO2 ea men ) and he condi ioning ea men unde eac ion eed s eam,
Model Ca alys cha ac e iza ion unde eac ion condi ions
123
he elec onic su ace p ope ies o he syn he ized P Cu3 nanopa icles we e s udied by
in si u APXPS unde wo king condi ions a di e en empe a u es.
F esh unsuppo ed P Cu3 nanopa icles we e p essed o o m a pelle abou 13
mm in diame e . An ini ial cha ac e iza ion o he esh sample was ca ied ou by
APXPS in ul a-high acuum condi ions in o de o eco d he s a e o he syn he ized
nanopa icles du ing he su ace cleaning me hod and be o e he condi ioning
en i onmen exposu e (see sec ion 3.2.2, chap e 3). Nex s ep was he in oduc ion o
he eac ion en i onmen in he analysis chambe . I mus be highligh ed he use o mass
low con olle o he pa ial p essu e con ol o he eac s. We we e he i s eam use s
in he s a up o he mass low con olle a he CIRCE beam ime o ALBA synch o on
ligh sou ce in Feb ua y 2018.
Mass lows sys em connec ed o he APXPS ends a ion is equipped only by ou
gas lines. I supposed he use o mix u e gas cylinde o O2 and CO2 [CO2/O2=4].
The e o e, due o he sys em limi a ions, he gaseous lux in oduced by mass low
con olle was 30mL/min H2 (gas line 1), 15 mL/min N2 (gas line 2), 3 mL/min CO (gas
line 3) and 15 mL/min O2+CO2 (gas line 4). 10% H2O was in oduced o he analysis
chambe using a bubble connec ed by UHV leak al e. The p essu e wo k in he
analysis chambe was 1.5 To . Feed s eam was in oduced a oom empe a u e and
sample was hea ing a 300ºC (hea ing a e 10ºC/min).
As i was showed in chap e 3, a e he su ace cleaning me hod, nanopa icles
p esen a Cu- ich su ace so co e-shell s uc u e. Howe e , nanopa icles composi ion
changes as a unc ion o he su ounding en i onmen . Thus, i s o all, dep h p o ile
analysis was ca ied ou o elucida e he nanopa icle composi ion du ing he
condi ioning ea men and eac ion s ep unde he same eed s eam.

Model Ca alys cha ac e iza ion unde eac ion condi ions
124
The chosen inciden pho on ene gies o ca ying ou he dep h p o iling we e
300, 548 and 1026 eV. Ob iously, acqui ed APXPS spec a we e no malized by he
pho on lux and he c oss sec ion o he analysis. Fo he inelas ic mean ee pa h
(IMFPs) calcula ion in his APXPS expe imen , we employed he TPP-2M o mula
p oposed by Tanuma e al. conside ing he nanopa icles as well-de ined P Cu3 alloy
wi h an only elec onic dis ibu ion. Consequen ly, he P 4 and Cu 3p IMFP o he
selec ed pho on ene gies we e 5, 8 and 13 Å espec i ely.
Figu e 5.7. Dependence o P and Cu composi ion o he P Cu3 nanopa icles du ing he
condi ioning ea men unde he eac ion mix u e a 300ºC.
Figu e 5.7 shows he dep h p o iling ca ied ou unde he eac ion en i onmen .
Su ace composi ion in he ou e shell (exci ed a hν =300 eV) was 74% Cu and 26% P ,
whe eas o he inne egion (exci ed a hν =1026 eV) was 60% Cu and 40% P . In
compa ison wi h he P 15Cu85 su ace composi ion ob ained unde CO2 en i onmen o
he su ace cleaning me hod (sec ion 3.2.2, chap e 3), i is obse ed om igu e 5.7 a
mig a ion o P a oms owa ds he su ace upon eac ion condi ions, eaching a close
P 26Cu74 composi ion on he su ace nanopa icles.
Model Ca alys cha ac e iza ion unde eac ion condi ions
125
A e he measu emen s a 300ºC du ing he condi ioning ea men in he
eac ion a mosphe e, sample was cooling down o oom empe a u e in he same
a mosphe e. Fo he p e e en ial oxida ion o CO es , P 4 - Cu 3p, C1s and O1s
APXPS spec a we e acqui ed a ou di e en empe a u es; oom empe a u e, 150ºC,
200ºC y 300ºC. Pho on ene gies o 300 eV o P 4 - Cu 3p, 450 eV o C1s and 700 eV
o O1s we e used o p oduce pho oelec ons wi h kine ic ene gies a ound 170 eV o
APXPS co e-le el spec a, co esponding o IMFPs in a ange o 5 and 8 Å. Figu e 5.8
shows he P 4 - Cu 3p spec a co espond o he su ace s a e a inc easing empe a u e.
Figu e 5.8 Ambien p essu e X- ay pho oelec on spec a o P 4 y Cu 3p eco ded o
unsuppo ed P Cu3 upon eac ion condi ions a di e en empe a u es.
Model Ca alys cha ac e iza ion unde eac ion condi ions
126
Be o e elucida ing he na u e o he P and Cu species, i is necessa y de ailing o
he obse ed changes in he su ace a omic dis ibu ion as a unc ion o he eac ion
empe a u e ( igu e 5.9). As men ioned be o e, shell o syn he ized P Cu3 nanopa icles
du ing he condi ioning ea men unde eac ion condi ion was composed by 74% o
coppe and 26% o pla inum. Howe e , he dec emen o he empe a u e o he
beginning o he ca aly ic eac ion leads o highe su ace Cu/P a omic a io. A oom
empe a u e, es uc u ing phenomena ook place and su ace Cu/P a omic a io
inc eased om 2.9 o 4.07 eaching a su ace P 19Cu81 composi ion. I means a
mig a ion o he coppe a oms o he su ace. Then, wi h he inc emen o empe a u e o
150ºC, su ace Cu/P a omic ac ion emained app oxima ely cons an (a ound 4.12).
Fo he o he hand, a u he inc emen o empe a u e in ol ed a d ama ic decline o
he a omic ac ion eaching alues o 2.8 a 200ºC and 2.4 a 300ºC. In e es ing, he
obse ed specie a 76.9 eV only appea a he same empe a u es when Cu/P a omic
a io is maximum. The e o e, o elucida e he na u e o he obse ed species, C 1s and
O 1s du ing he ca aly ic eac ion we e eco ded.
Figu e 5.9. Su ace Cu/P a omic a io o he syn he ized P Cu3 nanopa icles unde eac ion
condi ions a e he p oposed su ace cleaning me hod.
Model Ca alys cha ac e iza ion unde eac ion condi ions
127
Pho oemission lines o he P 4 and Cu 3p co e-le el con ain in all he
empe a u e ange di e en componen s. Fi s , single pla inum specie was obse ed in
all he ange o empe a u e wi h a ema kable P 4 7/2 peak a ound 71.0 eV and he
co esponding P 4 5/2 peak shi ed 3.3 eV o highe binding ene gies (L-S coupling). A
oom empe a u e, he peak is shi ed o 71.1 eV while he inc emen o empe a u e
supposes a shi o lowe binding ene gies (70.9 eV). Fo he o he hand, Cu 3p spec a
can be decon olu ed up o h ee spec al ea u es. Fi s ound peak a 74.3 eV was
assigned o Cu 3p3/2 componen o me allic coppe species. The Cu 3p1/2 con ibu ion
was i ed a 2.2 eV (L-S coupling). Second Cu 3p3/2 peak was ound a 75.3 eV. Bo h
species we e obse ed in all he empe a u es. Howe e , du ing he eac ion a oom
empe a u e and eac ion a 150ºC, a new Cu 3p3/2 componen a 76.9 eV was obse ed.
Figu e 5.11 shows he APXPS spec a o P 4 , Cu 3p, O 1s and C 1s du ing he
ca aly ic eac ion. In he condi ioning ea men s ep a 300ºC (Cu/P a omic a io
a ound 3), P 4 and Cu 3p spec um show con ibu ion o P 4 7/2 a 71.1 eV and h ee
con ibu ion o coppe species a 74.3, 75.3 and 76.9 eV. Due o he high hyd ogen
con en in he en i onmen (50%) and he empe a u e, condi ioning ea men unde
eac ion condi ions could be conside a e as educe ea men . In his way, Cu 3p3/2
componen a 74.3 was assigned o me allic coppe species. The shi o 1 eV o 75.3 eV
could be explained by wo op ions: i) oxidized coppe species (Cu+) o , ii) me allic
coppe species wi h de icien elec on densi y caused by he commen ed elec on
dona ion in he alloy om coppe o pla inum a oms (see sec ion 4.4.1).
Model Ca alys cha ac e iza ion unde eac ion condi ions
134
on he nanopa icles su ace. The loss o ca bon species wi h sp3 hyb idiza ion means
lowe eac i i y o he monolaye showing a change in he posi i e end in he CO
con e sion ( igu e 5.4b).
5.4 S uc u al ansi ions du ing P Ox eac ion
Fi s o all, X- ay abso p ion nea -edge s uc u e spec oscopy (XANES) has
been ex ensi ely applied o he s udy o he local elec onic and geome ical
en i onmen s o coppe and pla inum si es21–26. This echnique de ec s spec al changes
in he nea edge ea u e which appea as esonances cha ac e ized by he ene gy
posi ion and he in ensi y o he abso p ion edge27. Analysis o spec a makes possible a
de ini i e in e p e a ion o he syn he ized P Cu3 ca aly ic beha io .
5.4.1 Elec on densi y ans e du ing P Ox eac ion
Figu e 5.12 shows he in si u XANES spec a o syn he ized unsuppo ed P Cu3
nanopa icles a e he su ace cleaning me hod and du ing he p e e en ial oxida ion o
CO a oom empe a u e and 250ºC. Ini ial spec a a e he su ace cleaning me hod
we e aken unde He en i onmen . Sample was ac i a ed a 300ºC o 2 hou s (hea ing
a e 10ºC/min) by lowing 100 mL/min s eam eed based in he eac ion a mosphe e. I
is app eciable he same line shape o spec a and same whi e-line ene gy o he P L3-
edge (a) and same edge ene gy o he Cu K-edge (b) meaning he iden ical oxida ion
s a es in all he cases. Howe e , changes in he in ensi y o he Cu K-edge and P L3
whi e-line we e obse ed.

Model Ca alys cha ac e iza ion unde eac ion condi ions
135
Figu e 5.12. Compa ison be ween XANES spec a o he syn he ized P Cu3 nanopa icles a e he
su ace cleaning me hod and du ing he p e e en ial oxida ion o CO a oom empe a u e and 250ºC. a)
P L3-edge XANES spec a. The inse o pa (a) shows he magni ied P L3 whi e-line. b) Cu K-edge
XANES spec a. The inse shows he magni ica ion o Cu K-edge.
In pa icula , a he P L3-edge, he whi e-line (2p3/2 o 5d o bi als ansi ions)
in ensi y inc eases unde wo king condi ions e e ed o he condi ioning ea men
spec um. Acco ding o Mansou e al.28, he in eg a ed P L3 whi e-line a ea is
p opo ional o he numbe o unoccupied 5d s a es. A change in he occupied d-elec on
s a es could be expec ed by cha ge ans e wi h he eac ion en i onmen o wi h
coppe a oms o he alloy (see sec ion 3.2.3, chap e 3). In his way, he nanopa icles
exposu e o he eac ion a mosphe e leads o inc emen o he P L3 whi e-line and
spec a b oaden abou 8 eV abo e he abso p ion edge ( igu e 5.12a). This b oad
s uc u e is ela ed o hyd ogen abso p ion and Ankudino e al.29 explained ha i is
due o he change in he P po en ial by he P -H bonding.
Model Ca alys cha ac e iza ion unde eac ion condi ions
136
Reac ion a mosphe e is mainly composed by hyd ogen (a ound 50%), since he
elec onega i i y o pla inum (2.28) and hyd ogen (2.2) a e simila in he Pauling
scale30 ans e p ocess wi h he en i onmen a e expec ed. Wa a i and Ohnishi31 s udied
he changes in he elec onic s uc u e o P clus e du ing he hyd ogen adso p ion.
They concluded ha hyd ogen adso bed on pla inum su ace means he educ ion o he
whi e-line and he g ow h o he adjacen shoulde . Howe e , an inc emen o he P L3
whi e-line o he P Cu3 nanopa icles du ing he eac ion a mosphe e exposu e is
obse ed.
Despi e XANES analysis is based in he exci a ion o a oms om he en i e
nanopa icles, o al elec on densi y o a oms is s ong in luenced by he su ace species
and he eac ion-d i en es uc u ing. Mo eo e , Shin e al.32 s udied by DFT
calcula ions he in luence in he si e elec on densi y o CO and oxygen species
adso bed on he su ace P Cu co e-shell nanopa icles. They concluded he s onge CO
adso p ion in pu e me al han in P Cu sys ems showing an inc emen o C-O dis ance
wi h he coppe amoun . Coppe a oms ans e elec ons o pla inum a oms inc easing
he backbonding be ween pla inum and CO molecule which lead o C-O bond
elonga ion and elec on ich pla inum a oms. The e o e, ea angemen s o syn he ized
P Cu3 nanopa icles unde wo king condi ions in ol e changes in he elec onic densi y
o pla inum and coppe a oms.
The inc emen o he P L3 whi e-line means highe numbe o unoccupied d-
s a es and, he e o e, lowe s elec on densi y. O cou se, a modi ica ion o he pla inum
elec on densi y by coppe a oms is e lec ed in Cu K-edge spec a. As commen ed in
sec ion 3.2.3 (chap e 3), Cu K-edge in ensi y (1s o 4p ansi ion) is p opo ional o he
densi y o s a es so, inc emen o Cu K-edge means an inc emen o coppe elec on
Model Ca alys cha ac e iza ion unde eac ion condi ions
137
densi y. Thus, du ing he p e e en ial oxida ion o CO, an inc emen o eac ion
empe a u e in ol es highe elec on densi y ans e om coppe o pla inum a oms. I
is showed by he dec emen o he P L3 whi e-line and he Cu K-edge in ensi y ( illed
P 5d o bi als and dec emen o densi y o s a e o Cu). This elec onic ans e
elucida es he na u e o he Cu 3p3/2 APXPS peak a 75.3 eV. As he elec on densi y
ans e inc eases wi h he empe a u e, he peak a 75.3 eV assigned o elec on
de icien me allic Cu species inc eases.
Fo he o he hand, heo e ical hypo hesis p oposed by Shin e al.32 and Koma su
e al.33 based in he highe elec on densi y ans e om coppe o pla inum a oms wi h
he coppe amoun inc emen was e i ied. The op imized syn hesis me hod desc ibed
in sec ion 2.2.1 (chap e 2) allows he syn hesis o well-de ined P xCuy wi h di e en
mola a io. In his case, in e me allic P 1Cu1 nanopa icles we e syn he ized and
cha ac e ized by X- ay abso p ion spec oscopy ( igu e 5.13).
Model Ca alys cha ac e iza ion unde eac ion condi ions
138
Figu e 5.13. Compa ison be ween P L3-edge XANES spec a o P s anda d collec ed unde He
en i onmen and P 1Cu1 and P Cu3 nanopa icles acqui ed unde wo king condi ions a oom empe a u e.
The inse shows a magni ica ion o he P L3 whi e-line
Analysis o P L3-edge XANES spec a showed lowe P L3 whi e-line as coppe
amoun inc eased con i ming he highe elec on densi y ans e . I concludes ha he
di e ence ea angemen s o P Cu3 nanopa icles obse ed by APXPS as a unc ion o
he eac ion empe a u e.
5.5 Conclusions
In his chap e , ca aly ic ac i i y o he p e e en ial oxida ion o CO (P Ox
eac ion) o he syn he ized P Cu3 nanopa icles a e he su ace cleaning me hod has
been e alua ed. Nanopa icles showed di e en ca aly ic beha io as a unc ion o he
su ace ca bon deposi s p esence o absence. In his sense, Nanopa icles condi ioned in
hyd ogen en i onmen o unde d y eac ion mix u e en i onmen eached highe alues
o CO con e sion ha nanopa icles condi ioned unde CO2 en i onmen o unde we
eac ion mix u e en i onmen . The simula ion o he ca aly ic eac ion by in si u APXPS
ela ed he highe ca aly ic ac i i y wi h he p esence o su ace ca bon deposi s.
Su ace-d i en es uc u ing phenomenon unde wo king condi ions was s udied.
The exposu e o he eac ion en i onmen a oom empe a u e and 150ºC leads o
su ace coppe en ichmen . The na u e o he su ace ca bon and oxygen species had
been desc ibed by APXPS analysis. Resul s concluded ha he in e ac ion be ween
nanopa icles su ace and he oxidized ca bon species depend on he s acking deg ee o
he ca bon mul i o single laye s. Maximum CO con e sion alues we e ela ed wi h he
Model Ca alys cha ac e iza ion unde eac ion condi ions
139
p esence o su ace ca bon monolaye s composed by ca bon a oms wi h sp2 and sp3
hyb idiza ion.
Mo eo e , he exposu e o he eac ion mix u e en i onmen also leaded o an
elec on densi y ans e om coppe o pla inum a oms. This elec onic ans e
inc eases wi h he empe a u e.
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