1
Tomog aphichea ingholde  o insi uTEM:
S udyo P /CandP Pd/Al2O3ca alys s
asa unc iono  empe a u e
Lionel C. Gon a d,1,* Ra al E. Dunin-Bo kowski,2 Asunción Fe nández,1
Dogan Ozkaya,3 and Takeshi Kasama4
1 Ins i u o de Ciencia de Ma e iales de Se illa (CSIC), 41092, Se illa, Spain
2 E ns Ruska-Cen e o Mic oscopy and Spec oscopy wi h Elec ons (ER-C) and Pe e
G ünbe g Ins i u e (PGI), Fo schungszen um Jülich, D-52425 Jülich, Ge many
3 Johnson Ma hey Technology Cen e, Bloun ’s Cou , Sonning Common, Reading
RG4 9NH, UK
4 Cen e o Elec on Nanoscopy, Technical Uni e si y o Denma k, DK-2800
Kgs. Lyngby, Denma k
Abs ac : A omog aphic hea ing holde o ansmission elec on mic oscopy ha can
be used o s udy suppo ed ca alys s a empe a u es o up o ~1500 °C is desc ibed. The
specimen is placed in di ec he mal con ac wi h a ungs en ilamen ha is o ien ed
pe pendicula o he axis o he holde wi hou using a suppo ilm, allowing
omog aphic image acquisi ion a high specimen il angles wi h minimum op ical
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shadowing. We use he holde o illus a e he e olu ion o he ac i e phases o P
nanopa icles on ca bon black and P Pd nanopa icles on γ-alumina wi h empe a u e.
Pa icle size dis ibu ions and changes in ac i e su ace a ea a e quan i ied om il
se ies o images acqui ed a e subjec ing he specimens o inc easing empe a u es. The
po osi y o he alumina suppo and he sin e ing mechanisms o he ca alys s a e shown
o depend on dis ance om he hea ing ilamen .
Keywo ds: in si u TEM, TEM specimen holde , pa icle g ow h, he e ogeneous
ca alysis, pla inum, ca bon black, pla inum-palladium, alumina
* email: lionel.ce e [email protected] . Phone: +34 954489576
1. In oduc ion
When s udying he e ogeneous ca alys s, which equen ly comp ise me al nanopa icles
on ca bon black o an oxide suppo , an impo an goal is o obse e he e olu ion o he
ac i e phase wi h empe a u e in he p esence o eac an gases. Ca aly ic ea men can
lead o changes in he su ace a ea o he suppo ed me al pa icles and hence ca aly ic
ac i i y due o p ocesses such as sin e ing. In o de o unde s and and con ol ca alys
p oduc ion, i is necessa y o s udy how he dispe sion and mo phology o bo h he
nanopa icles and he suppo depend on eac ion condi ions. Al hough phase diag ams
o small me al pa icles ha e been p oposed heo e ically based on he modynamics
(Ajayan & Ma ks, 1988), hey a e incapable o p edic ing nanopa icle shapes ha esul
om pu ely kine ic conside a ions. Recen ly, Ba na d e al. (2009) p oposed a
quan i a i e phase map o gold nanopa icles based on ab ini io calcula ions. Howe e ,
a u he complica ion is ha such he modynamic models do no ake in o accoun he
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ole o he suppo , which de e mines he s eng h o a achmen and he eby pa icle
mobili y and also he posibili y o phase ans o ma ions (Be e al., 1974; Taus e ,
1987; Sepúl eda e al., 1998; Gónzalez e al., 2009).
In si u ansmission elec on mic oscopy (TEM) e e s o echniques ha allow di ec
obse a ion o dynamic p ope ies a he nanoscale h ough imaging, spec oscopy o
di ac ion. Such echniques can be used o unde s and he kine ics o phase ansi ions
in he e ogeneous ca alys s and he impo ance o sin e ing mechanisms (Bena idez e
al., 2012; Hansen e al, 2013). Possible app oaches in ol e injec ing gas di ec ly in o an
en i onmen al TEM (ETEM) (Hansen e al., 2002) and/ o using dedica ed sample
holde s ha con ain ho s ages, gas o liquid cells, elec ical con ac s, ibe op ics and
lase s o illumina ing o hea ing he specimen while images a e acqui ed wi h a omic
spa ial esolu ion (Kamino e al., 2005; C eeme e al., 2010; Ca alca e al., 2012;
Me ha een e al., 2013). In si u expe imen s ha ha e made use o such ins umen a ion
a e nowadays common. Mos ecen esul s ha e included s udies o he ole o
p omo e s in Ru-based he e ogeneous ca alys s (Hansen e al., 2002), he oxida ion o
In, he eoxida ion o Si and he o ma ion o g aphene on MgO-suppo ed P
nanopa icles (Kamino e al., 2005; Peng e al., 2012), as well as pho odeg ada ion o
Cu2O and pho odeposi ion o P on a GaN:ZnO pho oca alys (Ca alca e al., 2012).
He e, we desc ibe a TEM specimen holde ha p o ides di ec con ac be ween a
specimen and a ilamen ha has a small he mal mass. The ilamen eaches a
empe a u e ha depends on he cu en lowing h ough i . The e is hen no need o use
a suppo ilm, which can p e en e ec i e he mal ans e and deg ade image
esolu ion. Kamino e al. (2005) de eloped a simila specimen holde , which was
4
equipped wi h a longi udinal ungs en wi e aligned pa allel o he o a ion axis o he
holde . In con as , he ilamen in ou holde is o ien ed pe pendicula o he holde axis
and has a na ow design, pe mi ing acquisi ion o images a high specimen il angles
(± 80°) wi h minimal op ical shadowing. This capabili y allows elec on omog aphy o
be used o analyse he e ogenous ca alys s in h ee dimensions in combina ion wi h high
empe a u e hea ing expe imen s.
We demons a e he unc ionali y o he holde by imaging he g ow h o P ca alys
nanopa icles on ca bon black in si u in he TEM as a unc ion o empe a u e and by
measu ing he esul ing changes in pa icle size dis ibu ion (PSD) and su ace a ea o
he ac i e phase. We also s udy he o ma ion o bime allic P Pd pa icles on γ-Al2O3
and use high-angle annula da k- ield (HAADF) scanning TEM (STEM) (Gon a d e al.,
2008, 2009) o ob ain h ee-dimensional in o ma ion abou he po osi y o he suppo
a e successi e hea ea men s.
2. Ma e ials and Me hods
2.1. Tomog aphic hea ing holde
The omog aphic specimen holde ha we desc ibe he e con ains a p e-wound ungs en
ilamen aken om a ligh bulb (Fig. 1). We moun he ilamen in a emo able
ca idge, which is clamped on o wo elec ical con ac pads in a specimen holde om
E.A. Fischione Ins umen s, Inc. (Expo , PA). We glue he ilamen on o wo pieces o
a coppe g id using sil e epoxy and place a hin elec ically-insula ing shee o mica
be ween he coppe and he clamp.
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Samples can be deposi ed di ec ly on o he wi e, ei he in he o m o a d y powde o
om solu ion. The ends o he wi e, which has an elec ical esis ance o app oxima ely
5 Ω and can be eplaced be ween expe imen s i equi ed, can be accessed elec ically
om ou side he mic oscope. The wi e empe a u e, which can be calib a ed using an
op ical py ome e be o e inse ion in o he TEM column, p o ed o be highly
ep oducible be ween di e en ilamen s. Fo example, a empe a u e o ~1000 °C was
achie ed by passing a cu en o ~90 mA h ough he wi e. When ope a ed in high
acuum, he ilamen s we e ypically ound o ail a cu en s o ~220 mA,
co esponding o a empe a u e o jus o e 1500 °C. Tungs en wi e has high he mo-
mechanical s i ness and he e o e does no sag signi ican ly a high empe a u e, as
well as a high mel ing poin o 3422 °C and a low apou p essu e. Expe imen s we e
pe o med wi h ilamen s ope a ed o up o 12 hou s a cu en s o up o 150 mA
(co esponding o a empe a u e o ~1300 °C) wi h no signi ican signs o ungs en
e apo a ion.
2.2. P suppo ed on ca bon black
P pa icles wi h high dispe sions (> 75 m2 g-1), which we e suppo ed on mesopo ous
high-su ace-a ea ca bon blacks (Vulcan XC-72R) P (19.1 w %) and had been educed
in a N2 a mosphe e a 900 °C, we e p o ided by he Johnson Ma hey Technology
Cen e in he o m o a d y powde (Ralph & Hoga h, 2002; Ozkaya e al., 2003). The
samples a e used in p o on exchange memb ane uel cells, which equi e high loadings
o elec oca alys s. A small amoun o powde ha had been s o ed in ai was placed
di ec ly on o he ilamen o he hea ing holde , inse ed in o a Philips CM300 TEM

6
ope a ed a 300 keV and ehea ed in si u by passing a cu en h ough he ilamen . The
empe a u e was g adually inc eased om oom empe a u e o 975 °C in s eps o ei he
25 o 50 °C, allowing he specimen o s abilise be ween each s ep be o e acqui ing a
b igh - ield (BF) TEM image. Measu emen s o PSDs om he eco ded images we e
ob ained using dedica ed image p ocessing so wa e based on adap i e segmen a ion
(Gon a d e al., 2011).
2.3. P Pd suppo ed on alumina
P Pd nanopa icle o ma ion was s udied in si u in he TEM, s a ing om a d y powde
o he p ecu so (P (HN3)4)2 Pd2(EDTA) 2.5 w . % on γ-Al2O3 (SFC-140). γ-Al2O3 is a
me as able poly ype o Al2O3, which is used ex ensi ely as a ca aly ic suppo ma e ial
because o i s high po osi y and la ge su ace a ea. In he p esen specimen, he
o ma ion o P Pd pa icles was expec ed o occu a empe a u es o be ween 600 and
850 °C. The expe imen al p ocedu e was as ollows: (1) The powde was placed on o
he ilamen o he hea ing holde and inse ed in o a Tecnai F20 TEM. A egion o he
specimen ha could be il ed o high angles wi hou shadowing was iden i ied. A il
se ies o HAADF STEM images o he egion o in e es was acqui ed a low
magni ica ion o e a specimen il ange o -52° o +42° using a 4° il inc emen ; (2)
In si u hea ing was pe o med in a Philips CM300 TEM, wi h he empe a u e o he
ilamen inc eased om 500 o 850 °C, allowing he specimen o equilib a e be ween
s eps. BF TEM images we e acqui ed om he same a ea a high magni ica ion a each
empe a u e; (3) The specimen was allowed o cool o oom empe a u e, he holde was
einse ed in o he Tecnai F20 TEM and a new il se ies o HAADF STEM images was
acqui ed om he same a ea. Alignmen and omog aphic econs uc ion using he
7
simul aneous i e a i e econs uc ion echnique (SIRT) we e ca ied ou in Inspec 3D
so wa e (15-20 i e a ions). Vol ex isualiza ion o he inal econs uc ions was
pe o med using Ami a V2.3 so wa e. PSDs we e measu ed using image p ocessing
so wa e based on adap i e segmen a ion (Gon a d e al., 2011).
3. Resul s
3.1.
Sin e ing o P pa icles on C
Figu e 2 shows a se ies o BF TEM images, which illus a e he sin e ing o P pa icles
suppo ed on ca bon black du ing in si u hea ing a inc easing empe a u e. E en hough
he specimen had al eady been educed in an ine a mosphe e a high empe a u e,
Fig. 2 shows ha e-sin e ing occu s du ing hea ing in high acuum, beginning a
~550 °C, accele a ing be ween 650 and 850 °C and appea ing o s op a 850 °C.
Face ing o he pa icles can hen be seen, pa icula ly o se e al la ge pa icles. The
shape o he C suppo does no change app eciably du ing sin e ing, al hough i o a es
and ansla es wi hin he ield-o - iew. In Figs. 3A and B, ci cles and a ows a e used o
highligh di e ences be ween he same pa icles iewed a 500 and 900 °C.
Figu e 4 shows PSDs o he nanopa icles measu ed om selec ed images in Fig. 2.
Se e al s a is ical pa ame e s a e plo ed, including mean size, s anda d de ia ion and
maximum size, o i e selec ed empe a u es (500, 650, 725, 875 and 950 °C). The
mean pa icle size was used o es ima e he ac i e su ace a ea . This is an
impo an quan i y in ca alysis, as i desc ibes he su ace a ea o he ac i e phase ha is
exposed o gases and can be used o unde s and ca alys deac i a ion. We made wo
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app oxima ions: (1) Tha he con ac su ace o he nanopa icles wi h he suppo is
exposed o he gas; (2) ha he pa icles ha e sphe ical shapes wi h adii . The su ace
a ea is hen simply gi en by he exp ession
 


 4
∙4
3

 3
∙


whe e  is he numbe o pa icles,  and  a e he su ace a ea and mass o pa icle 
and  is he densi y o P (i.e., 21.450 kg m
⁄). Figu e 5 shows measu emen s and he
e olu ion o  wi h empe a u e. The a e o loss o ac i e a ea calcula ed om he
slope o a linea i , i.e.,  
⁄910mkg
⁄C.
3.2. Fo ma ion o P -Pd pa icles
Figu e 6A shows TEM images o he p ecu so (P (HN3)4)2 Pd2(EDTA) 2.5 w . % on γ-
Al2O3 (SFC-140) eco ded a oom empe a u e. Figu e 6B shows an image o he same
egion o he specimen eco ded a e hea ing a 850 °C. The images on he le side o
he igu e a e HAADF STEM images, in which he local in ensi y is sensi i e o a omic
numbe (b igh e egions co espond o pa icles). The BF TEM images shown in he
igh column o Fig. 6 we e acqui ed om he egions ma ked using ec angles in he
le column. The images show ha he P Pd pa icles g ow a high empe a u e and ha
he γ-alumina suppo inc easse in po osi y. Figu e 6C shows he measu ed PSDs o he
P Pd nanopa icles.
Figu e 7 shows indi idual HAADF STEM images eco ded a di e en specimen il
angles om he same a ea o he alumina sample be o e and a e hea ing, aken om a
il se ies o images used o elec on omog aphy. Figu e 8A shows a ol ex
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isualisa ion o he h ee-dimensional econs uc ion o his egion o he specimen a e
hea ing, while Fig. 8B shows an o hoslice gene a ed om he econs uc ed olume.
Al hough he il s ep o 4° used o acquisi ion o he il se ies is ela i ely la ge and
educes he spa ial esolu ion o he econs uc ed olume, his alue was chosen o
minimise he o al elec on dose on he specimen. Fo example, i has been obse ed on
samples o Pd suppo ed on alumina ha unde elec on i adia ion Al2O3 can be
educed and a me as able in e me allic compound o Al2Pd can o m (Kamino e al.,
1992). In he p esen expe imen s, he il ange used was smalle han he maximum
ange ha he holde allows (± 80°), which also a ec s he quali y o he inal
econs uc ion, in pa icula in he z di ec ion.
4. Discussion
The esul s shown in Figs. 1 o 8 can be used o discuss he kine ic ou e ha ca alys
nanopa icles ollow when hey g ow on a speci ic suppo and o de e mine he ela i e
impo ance o di e en sin e ing mechanisms (Bena idez e al., 2012; Hansen e al.,
2013). Th ee possible sin e ing mechanisms a e: (1) Coalescence, in ol ing mo ion o
he pa icles o e he suppo and usion (Ruckens ein & Lee, 1984). In gene al, a
empe a u es o 0.5 × he mel ing poin , me allic pa icles a e expec ed o be in a quasi-
mel ed s a e (con inuously luc ua ing be ween di e en s uc u es), which a ou s
coalescence (Ajayan & Ma ks, 1988; Ba na d e al., 2009). (2) Os wald ipening,
in ol ing he mig a ion o indi idual a oms om he pa icles on o he suppo , ac oss
he suppo and on o o he pa icles (Simonsen e al., 2010). Os wald ipening is
s ongly dependen on a omic di usi i y (Linde o h e al., 1997; Ho ch e al., 1999) and
can also happen in ace ed pa icles in he o m o inhibi ed nuclea ion, which a ises
16
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
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Figu e 1. (A) Modi ied TEM specimen holde wi h ungs en hea ing ilamen o ien ed
pe pendicula o he holde axis. The numbe s co espond o (1) he clamp; (2) an
insula ing mica shee ; (3) Cu elec ic con ac s; (4) sil e epoxy esin. (B-D) Th ee
magni ied images o he ilamen . The la ge a ow in (D) indica es an agg ega e o he
deposi ed specimen.
21
Figu e 2. Se ies o BF TEM images showing sin e ing o P nanopa icles on a ca bon
black suppo as a unc ion o empe a u e be ween 500 and 975 °C. The specimen was
deposi ed di ec ly on o he ungs en ilamen in he modi ied side-en y TEM specimen
holde shown in Fig. 1. The da k con as a he bo om le co ne o he images
acqui ed a 925 and 950 °C a ises om he closes pa o he ilamen o he egion o
in e es .

22
Figu e 3. (A) and (B) De ail ex ac ed om he BF TEM images shown in Fig. 2,
illus a ing he coalescence o P nanopa icles be ween indica ed specimen
empe a u es o 500 and 975 °C. Red ci cles in bo h images show he ini ial and inal
con igu a ions o selec ed P pa icles ha ha e coalesced. Whi e a ows indica e
pa icles ha emained s ongly a ached o he suppo and expe ienced smalle changes
in hei size. (C) De ail o he a achemen o a ace ed P nanopa icle o he suppo .
(D) Model showing c ys alline ace s and possible P (111) con ac plane o a P
nanopa icle such as ha shown in (E). (E) Expe imen al high- esolu ion TEM image o
one P pa icle on g aphi ised ca bon ( eco ded om a simila specimen) showing
a omic de ec s p esen a he su aces (a ows 1 and 2) (Gon a d e al., 2007).
23
Figu e 4. Top: Pa icle size dis ibu ions (PSDs) o he P pa icles shown in Figs. 2 and
3 measu ed a i e selec ed empe a u es be ween 650 and 950 °C i ed wi h logno mal
cu es. Bo om: Dependence o se e al s a is ical pa ame e s (mean size, s anda d
de ia ion and maximum size) on empe a u e. The alues inc ease wi h empe a u e
because o pa icle sin e ing.
24
Figu e 5. Ac i e su ace a ea o he P pa icles desc ibed in Figs. 2-4, measu ed a i e
selec ed empe a u es be ween 650 and 950 °C (see ex o de ails). Al hough he
e olu ion o su ace a ea is no linea we used he slope o a linea app oxima ion as an
es ima e o he a e o loss o ac i e su ace a ea.
25
Figu e 6. (A, B) ADF STEM images (le ) and BF TEM images ( igh ) o
(P (HN3)4)2Pd2(EDTA) 2.5 w % on γ-Al2O3 acqui ed (A) a oom empe a u e (using
he Tecnai F20) and (B) a e inc easing he empe a u e o 850 °C (using he Philips
CM300) in high acuum condi ions. The P Pd pa icle size and he po osi y o he
alumina di e be ween he ma ked zones. (C) PSDs measu ed om zones 2 and 3 and
om zone 3 alone, illus a ing he o ma ion o wo amilies o pa icles wi h di e en
a e age sizes.