Influence of Gold on Ce-Zr-Co Fluorite-Type Mixed Oxide Catalysts for Ethanol Steam Reforming

Ca alys s 2012, 2, 121-138; doi:10.3390/ca al2010121 ca alys s ISSN 2073-4344 www.mdpi.com/jou nal/ca alys s 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. 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