Ca alys s 2012, 2, 121-138; doi:10.3390/ca al2010121
ca alys s
ISSN 2073-4344
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A icle
In luence o Gold on Ce-Z -Co Fluo i e-Type Mixed Oxide
Ca alys s o E hanol S eam Re o ming
Julio Cesa Va gas
1
, S e lana I ano a
2
, Sébas ien Thomas
3
, Anne-Cécile Roge
4
and
Vé onique Pi chon
4,
*
1
Depa amen o de Ingenie ía Química y Ambien al, Uni e sidad Nacional de Colombia, Ciudad
Uni e si a ia, A enida Ca e a 30 No. 45-03, Bogo á Edi icio 453, Colombia;
E-Mail: [email p o ec ed]
2
Ins i u o de Ciencia de Ma e iales de Se illa, Cen o Mix o Uni e sidad de Se illa—CSIC, A enida
Amé ico Vespucio, N° 49, Isla de la Ca uja, Se illa 41092, Spain; E-Mail: [email p o ec ed]
3
Labo a oi e Ca alyse e Spec ochimie, ENSICAEN, Uni e si é de Caen, CNRS, 6 Boule a d
Ma échal Juin, Caen Cedex 14050, F ance; E-Mail: [email p o ec ed]
4
Labo a oi e des Ma é iaux, Su aces e P océdés pou la Ca alyse, ECPM, Uni e si é de S asbou g,
CNRS, 25 ue Becque el, S asbou g Cedex 2-67087, F ance; E-Mail: [email p o ec ed]
* Au ho o whom co espondence should be add essed; E-Mail:
[email p o ec ed].
Recei ed: 9 Janua y 2012; in e ised o m: 18 Janua y 2012 / Accep ed: 27 Janua y 2012 /
Published: 3 Feb ua y 2012
Abs ac : The e ec o gold p esence on ca bon monoxide oxida ion and e hanol s eam
e o ming ca aly ic beha io o wo Ce-Z -Co mixed oxides ca alys s wi h a cons an Co
cha ge and di e en Ce/Z a ios was in es iga ed. The Ce-Z -Co mixed oxides we e
ob ained by he pseudo sol-gel like me hod, based on me allic p opiona es polyme iza ion
and he mal decomposi ion, whe eas he gold-suppo ed Ce-Z -Co mixed oxides ca alys s
we e p epa ed using he di ec anionic exchange. The ca alys s we e cha ac e ized using
XRD, TPR, and EDXS-TEM. The p esence o Au in doped Ce-Z -Co oxide ca alys
dec eases he empe a u e necessa y o educe he cobal and he ce ium loaded in he
ca alys and a o s a di e en eac ion pa hway, imp o ing he ace aldehyde ou e by
e hanol dehyd ogena ion, ins ead o he e hylene ou e by e hanol dehyd a ion o me hane
e-adso p ion, hus inc easing he ca aly ic ac i i y and selec i i y in o hyd ogen.
Keywo ds: e hanol s eam e o ming; hyd ogen; gold; ce ium-zi conium-cobal mixed oxides
OPEN ACCESS
Ca alys s 2012, 2
122
1. In oduc ion
Ene gy is he key elemen in he in e ac ion be ween na u e and socie y and is conside ed as an
essen ial equi emen o he economic de elopmen [1]. Nowadays, 87% o he p ima y ene gy
demand is ob ained om non- enewable esou ces wi h limi ed a ailabili y as ossil and nuclea
sou ces [2]. In addi ion, he ene gy p oduc ion om adi ional sou ces is conside ed o be pollu ing
and unsus ainable. Ca bon dioxide emissions du ing he ene gy gene a ion om he ossil uels ha e
become one o he p incipal en i onmen al p eoccupa ions in he las ew yea s, since i is conside ed
as a majo pa icipan o global wa ming. In he nea u u e, i is necessa y o p oduce ene gy using
al e na i e sou ces, conside ed as enewable, sus ainable, e icien , sa e and economically
a ac i e [3]. Fo his pu pose, he use o hyd ogen as an e icien and clean uel is an in e es ing
al e na i e o he u u e way o p oduce ene gy, bu only i ob ained om a sus ainable sou ce.
Hyd ogen p oduced om bio uels such as bioe hanol, ob ained by biomass e men a ion, has a g ea
po en ial o p oduce sus ainable ene gy [4,5].
The global eac ion o s eam e o ming o e hanol can be ep esen ed by he ollowing gene al
Equa ion 1:
CH
3
CH
2
OH + 3 H
2
O = 2 CO
2
+ 6 H
2
(1)
Howe e , di e en pa allel eac ion pa hs exis , such as dehyd a ion in o e hylene, dehyd ogena ion
in o ace aldehyde, condensa ion o ace one and c acking eac ions [6–8]. The ela i e con ibu ion o
he di e en ou es depends on he na u e o he suppo , he ac i e phase and he condi ions o he
p ocess, as can be seen in Scheme 1.
Scheme 1. Possible pa h ou e in s eam e o ming o e hanol.
Ca alys s 2012, 2
123
Many ac i e species ha e been e alua ed o he s eam e o ming o e hanol: noble (Rh, Ru, Re, Pd,
I , P , Rh-P , Rh-Pd, Ru-P ,) and ansi ion (Ni, Cu, Co) me als suppo ed on me al oxides, wi h a wide
ange o acid-base and edox p ope ies, which ha e been he subjec o se e al e iews in he las
yea s [4,5,9,10]. Some ca alys s based on coppe and nickel e ealed in e es ing ac i i ies [11–14] bu
among he sys ems epo ed in he li e a u e, he use o cobal o hodium-based ca alys s as ac i e
phase seems o gi e he mos p omising esul s [15,16]. Al hough bime allic noble/ ansi ion-based
ca alys (Rh-Co, Ru-Co, Rh-Ni) s udied o his eac ion showed in e es ing esul s [17,18], suppo s
wi h oxygen mobili y, such as CeO
2
and CeO
2
-Z O
2
, ha e ecei ed special a en ion since hey a e
expec ed o ac as p omo e s in imp o ing he ca aly ic s abili y and p e en ing ca bonaceous
o ma ions [19,20].
The e hanol s eam e o ming p oduc s (ca aly ic selec i i y) a e he esul o a complica ed ne wo k
o eac ions s ongly in luenced by he ac i e phase oxida ion s a e [21,22], he na u e o he suppo ,
he ac i a ion p ocess, he wa e /e hanol a io, he eac ion empe a u e and he con ac ime be ween
he eac an and he ca alys [5,6]. Fu he mo e, he eac ion condi ions induce changes in he ca alys
physico-chemical p ope ies (i.e., addi ional educ ion o ac i e phase, solid s a e eac ions,
sin e ing, e c.) and he e o e in he ca aly ic selec i i y and s abili y.
In some ea lie publica ions, i was epo ed ha he inse ion o Co, as ac i e phase [23–25] in o
he Ce-Z mixed oxides and he subsequen doping wi h Rh [26,27], imp o e he ca aly ic s abili y and
selec i i y o e hanol s eam e o ming.
In his wo k, he in luence o gold on Ce-Z -Co mixed oxides, wi h di e en Ce/Z a ios, is
e alua ed in he eac ion o s eam e o ming o e hanol. The phase Ce-Z -Co on i s own is al eady
iden i ied as ac i e o his eac ion, bu he use o gold could p omo e he ac i i y and a ec s he ou e
o p oduc ion o hyd ogen going h ough he ace aldehyde in e media e [28]. The ca alys s we e also
es ed in he eac ion o CO oxida ion o which gold is known o be he mos ac i e me al when
p esen as nanosized pa icles [29]. The choice o s udying his eac ion was made because gold
suppo ed on he ype o suppo s as p epa ed o his wo k has no ye been explo ed o his eac ion,
bu also because CO oxida ion se es as a p obe eac ion o bo h elec onic and geome ic ac o s.
The oxida ion o ca bon monoxide by oxygen is a eac ion which is desc ibed in he li e a u e as being
sensi i e o he pa icle size, he suppo educibili y and he in e ac ion o gold wi h he suppo [30].
2. Expe imen al
2.1. P epa a ion o he Ca alys s
2.1.1. P epa a ion o he Ce-Z -Co Mixed Oxides
Two Ce-Z -Co mixed oxides, (Ce
w
Z
y
Co
0.9
O
8−δ
, w + y = 3.1), we e syn hesized by a pseudo sol-gel
me hod, based on he he mal decomposi ion o p opiona e p ecu so s, as epo ed by Va gas e al. [23].
The s a ing ma e ials o Ce, Z and Co we e ce ium (III) ace a e hyd a e, zi conium (IV)
ace ylace ona e and cobal (II) ace a e hyd a e, which all led exclusi ely o p opiona e p ecu so s in
p opionic acid. The sal s wi h concen a ion o 0.12 mol L
−1
we e dissol ed in boiling p opionic acid,
sepa a ely. The h ee boiling solu ions we e mixed and he sol en was e apo a ed un il a esin was
o med. The esin was he mally ea ed a 500 °C in ai by hea ing a a a e o 2 °C min
−1
o 6 h.
Ca alys s 2012, 2
124
2.1.2. P epa a ion o he Au/Ce-Z -Co Samples
The gold was subsequen ly deposi ed on he mixed oxide by a di ec anionic exchange (DAE) be ween
he suppo and a 10
−4
M solu ion o HAuCL
4
in o de o deposi 1 w .% o he gold. The chlo ine was
comple ely emo ed by an ammonia washing (4 M solu ion, 1 h) and a subsequen wa e washing, which
bo h imp o es he ac i i y and p e en s sin e ing, as epo ed by I ano a e al. [31]. The ca alys s we e
calcined in ai a 300 °C o 4 h wi h a amp a e o 5 °C min
−1
.
2.2. Cha ac e iza ions
The chemical analysis o Au and Cl was pe o med by induc i ely coupled plasma a om emission
spec oscopy ICPS a he CNRS Cen e o Chemical Analysis (Ve naison, F ance). The de ec ion limi
was 150 ppm o Cl. The analyses we e ca ied ou ollowing he calcina ion o he ca alys . The Au
weigh loading is exp essed as he pe cen age o Au pe weigh o calcined ca alys .
P e ious o he gold deposi ion, he mic o-homogenei y o he Ce-Z -Co samples was de e mined
by EDXS mic o-analysis on a TOPCON EM-002B appa a us (accele a ion ol age 200 kV).
The c ys allini y o he Ce-Z -Co mixed oxide was s udied by X- ay di ac ion (Siemens D5000,
Cu Kα adia ion, 20° < 2θ < 65°, 0.068 min
−1
).
The educibili y was s udied by The mo-P og ammed Reduc ion (TPR). Measu emen s we e
ca ied ou wi h a home-made appa a us equipped wi h a TCD on 50 mg o sample hea ed om oom
empe a u e o 900 °C a 15 °C min
−1
unde 3.85% H
2
/A mix u e (50 mL min
−1
).
2.3. Ca aly ic Tes s
2.3.1. CO Oxida ion
The eac ion was pe o med a a mosphe ic p essu e using a ixed bed qua z packed mic o- eac o
wi h 50 mg ca alys dilu ed in co die i e and a gas mix u e o 1.5% CO and 5% O
2
in He wi h a o al
low a e o 50 mL min
−1
(GHSV~23,000 h
−1
). The lows we e egula ed using Tylan mass low
con olle s. The ca aly ic eac ion was pe o med om oom empe a u e o 300 °C wi h a hea ing a e
o 5 °C min
−1
, wi h empe a u e moni o ed and con olled by a Eu o he m sys em. Analysis o bo h
CO and CO
2
we e pe o med by Rosemoun In a ed analyze s. The expe imen was epea ed se e al
imes in o de o measu e he ep oducibili y. Be o e each es , he ca alys was p e- ea ed a 300 °C in
ai o 2 h.
2.3.2. E hanol S eam Re o ming
The e hanol s eam e o ming eac ion was ca ied ou in a ixed bed eac o , a a mosphe ic
p essu e, using 160 mg o ca alys , hea ed a 2 °C min
−1
om oom empe a u e o 440 °C in an A /N
2
mix u e ( o al low: 35 mL min
−1
, 4:1 M, GHSV~5,000 h
−1
), wi hou any educ ion ea men . A e
1 h a 440 °C, he e hanol/wa e mix u e (15 mL min
−1
o mix u e in gas phase) was in oduced using
he same A /N
2
mix u e (GHSV: 26,000 h
−1
) as ca ie and he eac i e es was ca ied ou a 440 °C
o 5 h. The mix u e e hanol:wa e (1:6 mola ) in phase liquid was ed by using a Gilson HPLC pump
Ca alys s 2012, 2
125
o a e apo a o be o e he eac o inle , mixed wi h he ine gas mix u e and in oduced in o
he eac o .
The gas p oduc s we e analyzed on-line by mic o-gas ch oma og aphy o iden i y he p incipal
p oduc s and by-p oduc s (column Po aplo Q; column molecula sie e 5 Å) by di ec injec ion o he
e luen eac o s eam. No condensa ion o condensable p oduc s was pe o med.
The esul s a e exp essed in e ms o mola selec i i y in he gas phase o H
2
, CO
2
, CO, CH
3
CHO,
C
2
H
4
, CH
4
and CH
3
COCH
3
. When conside ing only he s eam e o ming eac ion, a maximum o 75%
o hyd ogen selec i i y can hen be achie ed wi h hose eac ion condi ions.
The hyd ogen yield is exp essed in g am o hyd ogen pe hou pe g am o ca alys , he maximum
H
2
yield which can be ob ained in he eac ion condi ions is 0.45 g H
2
h
−1
g
ca
−1
.
3. Resul s and Discussion
Two samples o Ce-Z -Co mixed oxides we e p epa ed, Ce
1.85
Z
1.25
Co
0.9
O
7.4
and
Ce
1.23
Z
1.87
Co
0.9
O
7.4
, and used as suppo s o gold con aining ca alys s. The sample wi h he highes
ce ium con en will be e e ed o as CeZ Co-A whe eas he ca alys wi h he highes Z con en will
be e e ed o as CeZ Co-B. The co esponding gold samples will hen be designed as Au/CeZ Co-A
and Au/CeZ Co-B.
The me allic elemen al composi ion o he samples, ob ained om ICPS and global EDXS analysis
(200 nm), was ound o be e y close o he expec ed heo e ical alue and showed a high deg ee o
homogenei y. The gold loading (ICPS) was close o he heo e ical alue o 1 w % and almos
ep oduced in he sys em wi h highe ce ium con en (0.96 w %). This has been al eady obse ed o
he ba e oxide sys ems [32]. As an example, o ca alys B, he heo e ical mola dis ibu ion is Ce
30.8%, Z 46.7%, Co 22.5%. ICP analysis ga e Ce 33.2%, Z 44.8%, Co 22.0% and he composi ion
om EDX analysis was Ce 33.0%, Z 44.7%, Co 22.3%. The Cl con en is unde he de ec ion limi
(150 ppm) which allows claiming ha he ca alys is almos chlo ine ee. Howe e , om he local
composi ion measu emen s (14.4 nm), EDXS analysis, some non-homogeneous composi ion zones a e
obse ed. Ne e heless, he sample wi h highe Ce/Z a io in he mixed oxides exhibi s he bes global
and local chemical homogenei y.
The di ac og ams o he CeZ Co mixed oxides, be o e and a e he gold deposi ion a e p esen ed
in Figu e 1.
The mixed oxides p epa a ion me hod o ba e Ce-Z -Co mixed oxides allows he c ys alliza ion
wi hou any no iceable phase ejec ion, showing he main cubic s uc u e o Ce-Z luo i e ype oxide.
No single ce ium o zi conium oxides a e de ec ed (CeO
2
, Z O
2
) and only a small weak peak
co esponding o cobal oxide spinel phase is p esen in he samples a 36° (Figu e 1a,b). Depending
upon Ce/Z a io, i can be no ed a shi o he di ac ion peak o lowe angles (2θ) o he sample wi h
high Ce/Z a io, which could be a ibu ed o he zi conium and cobal inse ion, bo h ha ing smalle
ionic adii compa ed o ce ium ionic adius. The o ma ion o mixed p opiona es du ing he
polyme iza ion s ep o he p epa a ion allows he o ma ion o he Co-O-Z and Co-O-Ce bonds as
well as Z -O-Ce bonds which ensu es he inse ion o cobal in he mixed oxide la ice.
A e he gold deposi ion on he mixed Ce-Z -Co oxide su ace, an addi ional di ac ion line is
isible a 2θ = 38.4°, co esponding o he Au(111) (Figu e 1c,d), wi hou ob ious changes in he main

Ca alys s 2012, 2
126
peaks co esponding o he luo i e s uc u e. Howe e , i is possible o obse e a shi in he main
di ac ion lines o he luo i e s uc u e, indica ing a modi ica ion in he deg ee o cobal inse ion in
he hos s uc u e, and esul ing in di e en in ensi ies in he cobal oxide and gold peaks di ac ion.
Fo he lowe ce ium con en samples (Figu e 1b,d), lowe di ac ion angles a e obse ed a e he
gold deposi ion. This beha io is a consequence o he di e en deg ee o acancies ini ially p esen in
he CeZ Co mixed oxide luo i e s uc u e as compa ed wi h hose gene a ed in he p esence o gold. A
simila beha io was no ed in gold/ce ia ca alys s [33,34].
Figu e 1. X-Ray Di ac og ams o : (a) CeZ Co-A; (b) CeZ Co-B; (c) Au/CeZ Co-A;
(d) Au/CeZ Co-B.
F om he X- ay di ac og ams, i is possible o calcula e he pa icle size o gold by means o
Debye-Sche e equa ion [35]. Wi h he inc ease o zi conium con en , he pa icles size dec eases
om 28 nm o Au/CeZ Co-A o 24 nm o Au/CeZ Co-B, which could be a ibu ed o a di e en
g a ing mode o he gold p ecu so on he ba e suppo s [30,32,36]. In any case, es ima ion o he size
by means o Debye-Sche e equa ion ends o lead o an o e es ima ion o he size as only la ge
pa icles unde go di ac ion. Un o una ely, i was no possible o achie e a mo e accu a e pa icle
size dis ibu ion because o he poo con as ob ained by ansmission elec on mic oscopy.
As he CeZ Co mixed oxide sys em was p epa ed o se e as a p ecu so o small cobal pa icles,
which is he ac i e phase in he e o ming eac ion [23,26], a special ca e o he educibili y o he
samples has o be aken. F om he educ ion p o ile TPR analysis (Figu e 2), i is possible o desc ibe
Ca alys s 2012, 2
127
and discuss he e ec o gold. The in luence o gold on he TPR p o iles is clea , as bo h he equi ed
empe a u es o ob ain he educ ion o he samples and he way ha educ ion occu s a e
ma kedly a ec ed.
Figu e 2. The mo-p og ammed educ ion (TPR) p o iles o samples: (a) CeZ Co-A;
(b) CeZ Co-B; (c) Au/CeZ Co-A; (d) Au/CeZ Co-B.
All he samples, independen ly o he Ce/Z a io o he p esence o Au, led o wo zones o
educ ion (Figu e 2). Fo Au ee samples (Figu e 2a,b), he i s educ ion zone is loca ed below
425 °C, whe eas i occu s below 300 °C o he Au-loaded samples (Figu e 2c,d). The i s educ ion
zone is asc ibed o he pa ial educ ion o he su ace ce ium om Ce
4+
o Ce
3+
along wi h he
simul aneous educ ion o he cobal species om Co
3+
and Co
2+
o Co
0
. The second educ ion zone a
high empe a u e co esponds o he educ ion o he Co
2+
inco po a ed in o he luo i e s uc u e and
o he educ ion o bulk ce ia [25,37].
The TPR he mog ams we e decomposed in o ou peaks. Fo Ce-Z -Co mixed oxides he e a e
h ee peaks in he educ ion zone I, a 150, 300, and 380 °C and a b oad peak in he educ ion zone II,
be ween 400 and 900 °C. The comple e desc ip ion o he he mog ams has been published elsewhe e
o sligh ly di e en samples. B ie ly, o he gold con aining Ce-Z -Co samples, wo peaks a 125 and
Ca alys s 2012, 2
128
200 °C a e loca ed in he i s educ ion zone and he second zone o empe a u e could also be
decomposed in o wo peaks loca ed a 380 °C and a b oad peak be ween 400 and 900 °C, espec i ely.
The small consump ion o hyd ogen cen e ed a a ound 150 °C (Figu e 2a,b) is a ibu ed o he
educ ion o highly dispe sed cobal oxide which is no inco po a ed in o he luo i e s uc u e. Fo he
gold-loaded samples, he e a e bo h changes in he amoun o H
2
which is sligh ly highe and a shi o
educ ion empe a u e owa ds a lowe alue. These wo phenomena con i m he ac ha he e a e
indeed small modi ica ions in he c ys alline s uc u e, as p o en by XRD. The amoun o cobal oxide
no inco po a ed in he luo i e s uc u e inc eases, i.e., small pa icles o cobal oxides a e p esen on
he suppo and hei educ ion is ac i a ed by he gold me allic pa icle.
By nume ical in eg a ion, i is possible o calcula e he con ibu ion o each species o he o e all
consump ion o hyd ogen and o es ima e he espec i e p opo ions o hyd ogen alloca ed o zone 1
and 2. By assuming ha , in he esh samples, gold is in a me allic s a e—gold usually unde goes
au o educ ion upon calcina ion and he p esence o me allic gold is p o en by XRD—and ha cobal
oxide, which is ini ially p esen as a s able oxide in he o m o (CoO.Co
2
O
3
) is comple ely educed
upon hyd ogen exposu e, i is possible o de e mine he pe cen age o Ce
4+
educed o Ce
3+
du ing he
TPR. The o e all hyd ogen consump ion pe g am o ca alys , he pe cen age o pa ial educ ion
(in zone 1) and he pe cen age o hyd ogen consumed by each species a e p esen ed in Table 1.
Table 1. To al hyd ogen consump ions, peak a ea dis ibu ion o samples and pe cen age
o ce ium educed a e TPR.
Samples Peak 1
(%)
Peak 2
(%)
Peak 3
(%)
Peak 4
(%)
Zone I
(%)
H2
(mLSTP g−1)
CeIV→CeIII
(%)
CeZ Co-A 5 24 9 61 39 68 47
Au/CeZ Co-A 11 27 21 41 38 76 70
CeZ Co-B 5 25 6 63 37 68 56
Au/CeZ Co-B 10 30 17 43 40 58 26
Fo he Au- ee samples, he hyd ogen consump ion om he i s h ee peaks o educ ion is quasi
iden ical (1.2 × 10
−3
mol g
−1
H
2
o CeZ Co-A and 1.1 × 10
−3
o CeZ Co-B). The di e ence be ween
hese alues and he calcula ed hyd ogen consump ion needed o comple e cobal species educ ion
could di ec ly p o ide he pe cen age o he su ace ce ia educ ion. Fo bo h samples, 39 and 37% o
ce ia su ace educ ion is ob ained, espec i ely. In addi ion, he unal e ed H
2
consump ion o he
peak 4 indica es a cons an quan i y o educed bulk Ce
+4
, no ma e he Z composi ion. The p esence
o Z does no seem o al e he educ ion o he bulk ce ium con en .
Howe e , he educ ion o cobal and ce ium changes in he p esence o gold being p omo ed by i s
p esence; he i s h ee peaks o cobal educ ion a e comple ely eposi ioned. Fo he i s peak, he
empe a u e o educ ion is lowe , bu he olume o consumed hyd ogen is doubled, indica ing he
highe con en o cobal species ejec ed om he luo i e s uc u e a e gold deposi ion. Mo eo e ,
he p esence o gold acili a es he Co
3+
o Co
2+
educ ion (peak 2) o which a dec ease o he
empe a u e o educ ion by 100 °C is obse ed. The amoun o hyd ogen consumed in his egion is
simila o all samples, which con i ms ha only cobal is in ol ed in his p ocess. The p esence o
gold no only induces small s uc u al changes as p o en by XRD bu modi ies he educibili y o he
Ca alys s 2012, 2
129
wo species co esponding o he low empe a u e peaks. The e is a highe educ ion deg ees a low
empe a u e obse ed o bo h ca alys s in he p esence o gold. This con i ms lowe bonding ene gies
o he oxygen on he su ace oxidized species and he e o e a highe mobili y and highe educibili y,
which gene a e acancies on he su ace o species wi h lowe oxida ion s a e which ac as ac i e si es
(in his case educing cobal ).
The hi d peak o educ ion seems a li le bi mo e complica ed o explain. I he consump ion is
caused only by Co(II) o Co(0) educ ion, he consump ion o hyd ogen should no change. Bu an
inc ease in he hyd ogen consump ion is obse ed and he empe a u e o educ ion emains
unchanged, indica ing a highe con ibu ion o he su ace ce ia educ ion. This is con i med by he
ac ha o he CeZ Co-B sys em, whe e he quan i y o Ce is lowe , he hyd ogen consump ion is
also lowe . Howe e , he calcula ions o he su ace ce ia con ibu ion o he educ ion p ocess show
e y simila alues, 38% o Au-CeZ Co-A and 40% o Au-CeZ Co-B. The la e indica es ha he
gold p esence p o okes cobal ejec ion o he luo i e s uc u e esul ing in a highe H
2
consump ion a
low empe a u e compensa ed by a highe su ace ce ia educ ion con ibu ion.
The high empe a u e peak o educ ion (>500 °C) co esponding o he bulk ce ium educ ion
shows a dec ease in e ms o hyd ogen consump ion when gold is p esen which can be di ec ly ela ed
o he inc ease o he su ace ce ia educ ion (Table 1).
Rega dless o he composi ion o he ca alys , he e exis s a empe a u e ange ee o educ ion o
all he samples, which allows he possibili y o clea ly dis inguish he zone o pa ial educ ion. This
allows he use o ca aly ic sys ems in which cobal is pa ially educed and is chemically s able a he
empe a u e a which he eac ion o e hanol e o ming occu s.
Fo CeZ Co samples, he zone I is he coun o peaks 1, 2, and 3. O he wise, he zone I in
Au/CeZ Co samples is he coun o peaks 1 and 2. By compa ing he pe cen age o educ ion o zone I
and II o gold con aining and no con aining samples, i is possible o obse e a simila a ea
dis ibu ion, in which he hyd ogen consump ion is nea o 40% o he o al one.
3.1. CO Oxida ion
The comple e oxida ion o ca bon monoxide is one o he mos s udied eac ions o
gold-con aining ca alys s since he as onishing disco e y o Ha u a e al. [29] ha e y small gold
nanopa icles exhibi ca aly ic ac i i y a sub-ambien empe a u e. The me hod o p epa a ion has a
g ea in luence on he ca aly ic beha io since i a ec s he gold pa icles’ size, mo phology and
oxida ion s a e. Fu he mo e, gold ca alys s ac i i y is in luenced by se e al pa ame e s such as acidi y
o basici y o he suppo , he he mal ea men o he na u e o ac i a ion p ocess [30]. The e o e he
CO eac ion se es as a p obe eac ion no only o he pa icle size bu also o e eal sub le changes in
he elec onic s a e o gold o in he mo phology o he pa icles, modi ica ions which o he echniques
a e a pains o e eal. The con e sion o ca bon monoxide as a unc ion o he empe a u e is p esen ed
in Figu e 3 o all he samples wi h o wi hou gold.
Ca alys s 2012, 2
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