The role ofNi on the performance of automotive catalysts:evaluating the ethanol oxidation reaction

The role of the nickel oxide on the ethanol oxidation reaction over different model catalysts and commercial catalyst wasstudied. At 473 K, the catalytic activity followed the order: Pd/ Al203 ~ Pd/Ce021 Ab03 ~ Pd/ Ab03 +NiOI Ab03 physi-cal mixture> Pd/NiO /AI203 ~ Pd/NiO /Ce02 /AI203 ~ commercial catalyst. NiOI Al203 and Ce021 Al203 catalysts werenot active at this temperature. Nickel addition strongly decreased the catalytic activity of PdlAb03 and Pd/Ce02/Ab03 cat-alysts. Temperature-programmed reduction (TPR) and oxygen storage capacity (OSC) measurements showed that palladiumpromoted the nickel oxide reduction. This strong interaction between both metals was destroyed under the reaction conditionsleading to a nickel oxide surface segregation. The decrease of ethanol conversion in the presence of nickel was due to thecoverage of palladium particles by nickel oxide, as demonstrated by IR analysis. The catalytic behavior of commercial catalystwas well represented by the PdINiOlCe021 AI203 model catalyst. The main products of ethanol oxidation were acetaldehyde,acetic acid, carbon oxides and ethyl acetate. Ethanol oxidation proceeds through parallel and series reactions. The nickeladdition shifted all the reaction system towards high temperature due to the decrease of activity.

All commercially produced gasoline blends con-tain organo-sulfur compounds in concentrations up to1000 ppm [1]. Combustion of a fuel containing sul-fur compounds results in the formation of S02 andS03, which can deactivate vehicle exhaust catalysts[1,2]. Several studies were carried out to investigatethe effects of sulfur as well as the mechanism of sul-fur poisoning of three-way catalysts (TWC) [1,3-5].Beck and Sommers reported that the activity for hy-drocarbon (HC) and NOx is deteriorated in the pres-ence of sulfur [I]. S02 formed can also be reduced to

* Corresponding author. Fax: +55-21-2263-6552.t;-mail address: appel@uo1.com.br (L.G. Appel).

H2S under specific vehicle operating conditions [6,7].To reduce H2S emissions, catalysts manufactures haveused different additives to catalyst formulation suchas NiO, Fe203 [8].

Nickel plays a role of a regenerable H2 S-trap,which retains H2 S formed under rich conditionsand is re-activated under lean atmosphere [6]. Thismechanism involves the formation of NiS04 underfuel-lean atmosphere. However, these additives canalso reduce the activity of TWC [7]. It is suggestedthat the catalyst deactivation is inhibited by mini-mizing the interaction between the TWC and nickelcompound. Andersen et al. [7] studied the mecha-nism of Ni deactivation of TWC. According to theauthors, the catalyst deactivation under redox (cycledreducing/oxidizing) aging was due to the formationof Pd-Ni alloy.

In addition to the high sulfur level, the Braziliangasoline has also around 20% of ethanol. The use ofethanol as fuel or fuel additives can reduce the emis-sion of conventional pollutants such as carbon monox-ide. On the other hand, the use of ethanol increasedthe direct emissions of unburned ethanoL acetalde-hyde and NOt [9]. Aldehydes in the atmosphere havebeen associated with a number of health effects suchas eye, nose and throat irritation, asthma attacks, anda potential human carcinogen [10]. It is well knownthat these compounds also participate in atmosphericphotochemical reactions that lead to the fonnation ofperoxyacetil nitrate [11].

Therefore, it is necessary that the usual catalyticconverter is able to control the emission of these com-pounds. Pd-Mo/A1203 catalysts were initially usedto control the exhaust emissions of ethanol-fueledBrazilian vehicles. It has been reported that the addi-tion ofMo03 to Pd/Ab03 catalysts improves the NOactivity with high selectivity to N2 [12 14]. Recently,Pd-Mol Ab03 catalysts were studied for the CO + NO[15-17], ethanol + NO [17] and acetaldehyde + NO[18] reactions. A redox mechanism was proposed toexplain the molybdenum promoting effect on Pd inthe CO + NO reaction. On the other hand, molyb-denum oxide does not promote the ethanol + NOreaction and this was attributed to different reactionmechanism. Pd-Mo/Ab03 catalyst showed higheractivity for the reduction of NO by acetaldehyde thanPd catalyst. However, the selectivity to N2 was nearlythe same, indicating that the mechanism was the sameon both catalyst.

Nevertheless, there is no infonnation about the ef-fect of oxygenated organic compounds on the catalyticproperties of Pd based catalysts containing Ni. Theaim of this work is to investigate the role of N i on theethanol oxidation over model and commercial auto-motive catalyst.

AI203 support was prepared by calcination of a),-alumina (Engelhard, AL-3916P) at 823 K, for 16 hin a muffle. Pd/AI203, NiO/Ab03 and Ce02/Ab03samples were prepared by dry impregnation of alu-

Table ICe. Ni and Pd content on the prepared and cummereial catalysts(without eordierita)

Pd'Alc03NiO!Ab03Pd!NiO! AbO,PdCeOcAlcO,Pd!NiO!CeOc!AbO,Commercial

094O.X5O.X8093

12.X913.07

33.2528.4732.39

mina with an aqueous solution of PdCb, Ni(N03h,Ce(N03 h, respectively. The solids were dried at343 K, for 16 h and calcined at 773 K, for 2 h (2 Klmin)under air flow. Pd/NiO/Al:z03, Pd/Ce02/Ab03 andNiOlCe021 Ab03 samples were prepared by im-pregnation of NiO/Ah03 and Ce02/Ah03 samplesusing the same procedure and precursors salts de-scribe above. PdlNiOICe02/A\:z03 was also obtainedby dry impregnation of NiOlCe02/AI203 by usingPdC\:z as precursor and the same thermal treatmentdescribed above. A physical mixture of Pd/ AI203and NiOI AI203 (I: 1 (w/w)) was prepared in anagate mortar. The commercial catalyst was made byhand-grinding in an agate mortar. The Ce, Ni andPd concentration of the model catalyst and of thecommercial catalyst are displayed on Table I.

2.2.1. Temperature-programmed reduction (TPR)Temperature-programmed reduction (TPR) experi-

ments were performed in a conventional apparatus, asdescribed previously [19]. Before reduction, the cat-alysts were heated at 423 K in flowing nitrogen for0.5 h. Then, a mixture of 4.7% hydrogen in nitrogenwas passed through the sample and the temperaturewas raised from 298 up to 773 K at a heating rate of10K/min.

2.2.2. Oxygen storage capacitv measurements(OSO

A pulse technique was used to determine the oxy-gen storage capacity (OSC) of the samples [20]. Thecatalyst (300 mg) was oxidized at 873 K, for 1h, un-der air flow and cooled to 703 K under nitrogen for

30 min. Then, the sample was reduced at 703 K undera 5% Hz in Nz (AGA) mixture (30 mUmin). Oxygenpulses (0.20 ml) were then performed at the same tem-perature.

2.2.3. Infrared spectroscopy ana(vsisInfrared spectroscopy analyses were perfonned in a

Magna 750-Nicolet apparatus. Each wafer containedapproximately 5 mg of catalyst diluted in 40 mg ofa-alumina. The samples were dried under Nz at423 K, during 1h, reduced with Hz at 773 K, forI h, and exposed to high vacuum during I h. Afterexposition to the reaction mixture at 393 K, during5 h, a primary vacuum was carried out during 15 min.The sample was then cooled to room temperatureand spectra were recorded. Afterwards, the samplewas heated to another temperature under the reactionmixture and the procedure previously described wasrepeated.

The catalytic tests were performed in a quartz re-actor at atmospheric pressure and the products weremonitored by on-line gas chromatography, with flameionization and conductivity detectors. Prior to reac-tion, the sample (28 mg of catalyst diluted in 120 mgof SiC) were reduced under Hz at 773 K, for 1h. Then,a 2% ethanol in air mixture (Oz/CzHsOH ratio of 6)obtained by passing air through a saturator containingethanol at 283 K was fed to the catalyst at the space ve-locity of 11,520 h-I. No deactivation of the catalystswas observed during the study. In order to have thesame amount of Pd in all catalytic test, 57 and 86 mgof physical mixture and commercial catalyst was used,respectively.

TPR profiles of Pd/Ah03, NiO/ AbO] and CeOz/Ab03 catalysts are presented in Fig. 1. Pd/ Ah03 ex-hibited one peak at 406 K. The reduction profile ofNiO/AIz03 showed one peak at 583 K and a Hz up-take at high temperature, presenting maxima around994 and 1106K. The CeOz/Alz03 catalyst displayed

a small hydrogen consumption around 789 K and apeak at 1194 K.

According to the literature, the hydrogen consump-tion at 406 K has been attributed to the reductionof PdO,Clr species [21]. In the case of NiO/A]z03catalyst, three reduction regions were identified: re-gion I (570 K), region II (700--900 K) and region III(1020~1150K) [221- The first one was assigned tothe nitrate decomposition. The second region cor-responded to the reduction of N j2+ species highlydispersed. This region was typical of catalysts con-taining high Ni content calcined at low temperature.The last one was due to the reduction of a NiAlz04phase fonned by the diffusion of Ni ions into thesupport and was mainly observed on catalysts cal-cined at high temperature. Therefore, in our work,the TPR profile of NiO/Alz03 catalyst revealed thepresence of nickel nitrate, Niz+ species highly dis-persed and nickel aluminate. Monteiro et al. [23] alsoperformed TPR analysis on CeOz/ Ah03 sampleswith different ceria loading. TPR profiles of 3 and20% CeOz/Alz03 showed several reduction peaks ataround 720, 870, 1135 and above 1150 K. The relativeintensity of these peaks were related to ceria loading.In the literature, these peaks have been ascribed todifferent ceria species. According to Shyu et al. [24J,the peak at around 720 K corresponds to reductionof ceria capping oxygen. The peaks at 870, 1000and above 1200 K were assigned to the fonnation ofnon-stoichiometric cerium oxides (CeO,), CeAI03and Cez03, respectively. Appel et al. [25J studied theinfluence of the precursor, calcination temperatureand cerium content on distribution of cerium speciesover alumina. TPR results also revealed the presenceof several reduction peaks, which were attributed tothe surface reduction of CeOz and to the formationofCeAl03 and Cez03. According to the literature, inthis work the Hz uptake corresponded to the reductionof ceria capping oxygen (867 K) and the fonnation ofCeZ03 (1160 K).

Fig. 2 exhibited the TPR profiles of the Pd/NiO!A1z03, Pd/CeOz/Alz03, I\iiO/CeOz/Ah03 and Pd/N iO/CeOz/ Alz03 catalysts.

The TPR profile of Pd/NiO/A1z03 showed threepeaks at 43 I, 729 and 979 K. It is important tostress that the TPR profile of Pd/NiO/ Ab03 didnot correspond to the addition of the reduction ofmonometallic catalysts. These results suggested the

300 400 500 600 700 800 900 10001100 1200 1300 1400

Temperature (K)

existence of an interaction between both metals. Thepeak at 431 K corresponded not only to palladiumoxide reduction but also to nickel nitrate since thehydrogen consumption was higher than the one onthe PdIAI203 (Table 2). Furthermore. the presenceof palladium shifted the peaks associated to the re-duction of superficial Ni2- and nickel aluminate tolower temperatures. Therefore. the palladium addi-tion to NiOI AI203 catalyst promoted the reduction ofnickel oxides. These results suggested the presenceof a strong interaction between palladium and nickeloxide.

Two peaks at 381 and 1148 K and a hydrogen uptakebetween 700 and 1200 K were observed on the TPRprofile ofPd/Ce02/AI203 catalyst. The peak at 381 Kwas ascribed to palladium oxide reduction whereasthe hydrogen uptake at high temperatures was due tothe formation of Ce203. However, the hydrogen con-

sumption at 381 K was higher than that necessary toreduce the palladium oxide (Table 2) suggesting thatreduction of ceria capping oxygen occurred at this re-gion. Therefore. the palladium addition promoted the

Table 2H2 consumption during TPR

Pd/AbO,Cc02/AI20,Pd/Cc02/A"bO,NiO/AI20,Pd',\iO/AI2(hNiO/CC02/AbO,PdNiO'Cc02AI20,

4573779R

14R3145021R9

"H2 consumption of the first peak remO\ing the palladiumoxide reduction.

1148

Pd/Ce02/Alp3729-::J

eci-c0:;::;

Pd/NiO/AIP30-E::J(f)C0c..>C\JI

NiO/CeO/ AIP3805 10431155

reduction of cerium oxide species, in agreement withMonteiro et al. [23].

The TPR profile of NiOlCe02/Ah03 catalyst dis-played three peaks at 548, 1091 and 1184 K and ashoulder around 1000 K. This profile was very similarto the ones of the monometallic catalysts, indicatingthat the presence of nickel oxide did not promote thecerium oxide reduction.

The PdINiOlCe02/Ah03 catalyst exhibited a verycomplex TPR profile, with peaks at 421, 674, 805,1043 and 1155 K. A comparison to the TPR ofNiOlCe02/Ah03 catalyst suggested that the palla-dium addition also promoted the reduction of thespecies presented on the NiOlCe02/Al203 catalystdue to the shift of the reduction regions to lowertemperatures.

Therefore, these TPR results revealed that palla-dium addition had an important promoting effect onthe reduction of both NiO and Ce02. According to[23], hydrogen is activated on metallic palladiumthrough dissociative adsorption to atomic hydrogen,which promotes the reduction of metal oxide.

The OSC values of the samples are displayed inFig. 3. The oxygen storage capacity ofPd/Ah03 sam-ple was slightly higher than the one of Ce02/Ah03.TPR results indicated that oxygen consumption ofOSC measurements was associated to the oxidationof completely reduced Pd whereas the OSC value ofCe02/Ah03 sample corresponded to the re-oxidation

~~ 300ub!J

N0 200or.0,)

"0 100E~u 0VJ r') ';0 r') r') r. t"'1 r') 0 00 0 0 0 0 ("'l N

("'l N N ("'l ("'l =< :;;:=< =< =< =< - --- 0::a --- --- --- --- 0("'l 0 0 ("'l ~0... 0 Z ~ 0 ~~ ~ NU U 0N ::a 0... 0,)0 U~ 0... --U -0Cl-

of superficial cerium oxide species. The oxygen stor-age capacity of NiO/Ab03 was indeed very low. Inthis case, the pretreatment before the OSC analysisdecomposed the nickel nitrate residues but it was notable to reduce the nickel oxide species. According toTPR analysis, their reduction took place at higher tem-peratures.

For the Ce02INiO/Ab03 sample, the OSC valuecorresponded practically to the sum of the oxygen up-take on NiO/Ab03 and Ce02/Ab03 samples. Thisresult agreed very well to the TPR profiles which didnot detect the presence of an interaction between J\iand Ce on this catalyst.

The OSC value of Pd/Ce021 Al203 sample washigher than that obtained by the addition of Pdl AI203and Ce02/Ab03 OSC values. Taking into accountthe TPR results, it can be suggested that the Ce02reduction is related not only to the superficial oxygenbut also to the oxygen from sublayers of the Ce02structure. Indeed, it is well known that Ce02 is ableto release and get oxygen atoms without significantchanges in its crystalline structure [26 J. This behavioris promoted by Pd at low temperatures.

As for PdlNiO/Ab03, the palladium addition toJ\i/A1203 sample strongly increased the OSC value.In accordance to TPR analysis, this result can be as-signed to the promoted reduction of Ni2+ dispersedspecies. Furthermore, the PdINiOI Ab03 sample hadan OSC value higher than Pd/Ce02/Al203 sample.This result is connected to the intrinsic redox prop-erties of each metal oxide, which produced differentoxygen consumption. During OSC measurements,

NiO and Ce3+ formed during pretreatment were oxi-dized to Ni2+ and Ce4+, respectively. This change inoxidation state corresponds to a more important oxy-gen uptake on the nickel based catalyst. U:iOf et al.[27 J reported the same behavior on a commercialcatalyst.

It is worth noting that the OSC value of PdlNiOICe021 Ab03 is smaller than the addition of PdlNiOIAI203 and Pd/CeOI Al203 ones. This result is relatedto the fact that the three samples have the same Pdconcentration, i.e. I wt.%. Thus the contact betweenpalladium and metal oxides is smaller on the catalystcontaining both additives.

Fig. 4 exhibited the infrared spectra after ethanoloxidation at different temperatures on Pd/A1203,

/r\ 14.05./ ( 1'\ (\, aJ /\ . VJ \\J1"v\

I \ I \f\b-/ (lVV~1652 !\1413 \

(V \ !\ 1334II J \ /, \ 1\ (I c

II'! Vl-JI ,\ 'II \J )427

/ (\1" I~ d/ ,I /0 \~~~!\VrJ'\ e

V \)1581 1463

--.. /i\. r", f

/\.J~/\ g

V~'-/~

Fig. 4. Infrared spectra alier ethanol oxidation at different temper-atures on the eatalysts--Pd/AI201: (a) 393 K, (e) 513K, (0 603 K:Pd/NiO/AbOl: (b) 393K, (d) 513K, (g) 603K: NiO/AbOl: (e)513 K.

NiO/Ah03 and PdINiO/Ah03 catalysts. It is impor-tant to stress that no signal related to the adsorptionof ethanol on alumina support was observed.

After reaction at 393 K (Fig. 4a), the IR spectrum onPd/Ah03 presented the following bands: 1581, 1463,1405 and 1334cm-1 and also shoulders at 1427 and1652 cm-I. The same bands can be observed after thereaction at 513 K (Fig. 4c). However, the intensity ofbands at 1652 and 1405cm-I decreased whereas theintensity of the bands at 1413 cm-I increased. Af-ter reaction at 603 K, only two bands at 1581 and1463 cm-1 were noted (Fig. 4f).Medeiros et al. [28] studied the ethanol oxidation

on Mo-Sn catalysts using the same procedure ofthis work. At room temperature, they observed thepresence of bands around 1450, 1390, 1266, 1089,1042 cm-I, which were assigned to ethoxy species.After reaction at 473 K, the appearance of bands at1527, 1435, 1387 and 1320cm-1 was associated tobridged and monodented carboxylate. However, onlythe bands characteristic of bridged carboxylate (1527and 1435 cm- 1) were observed after reaction at hightemperature (543 K).

Baldanza et al. [17] performed FTIR analyses of ad-sorbed ethanol on Ah 03 and PdIAh 03. The results re-vealed the presence of bands characteristics of ethoxyspecies at 1447, 1389, 1168, 1120, 1075cm-I. Bandsat 1585 and 1463 cm-I were attributed to the asym-metric and symmetric stretching acetate species, re-spectively, in agreement with [29]. As the temperaturewas raised, the band intensity of the ethoxy speciesdecreased while the band intensity related to acetatespecies increased.A comparison with literature data indicates that the

band at 1405 cm-1 is associated to ethoxy species. Theother bands can be attributed to carboxylate species.

In the case ofPdlNiO/Ah03 and NiO/Ah03 cata-lysts (Fig. 4b, d and e), the IR spectra were very sim-ilar to the one of PdIAI203 catalyst. However, thereare some differences that are worth to point out. OnPdlAh 03 catalyst, the intensities of the bands around1652 and 1413 cm-1 were higher than on the cata-lysts containing Ni. These vibrations corresponded tobridged carboxylates due to their position and t.v.The bands at 1334 and 1427cm-1 were associated tomonodented carboxylates [28-30].

After reaction at high temperature (603 K), theIR spectra of PdlAh03 and PdINiO/AI203 were

even more similar (Fig. 4f and g). Taking into ac-count the high stability of these species (1581 and1463cm-I), they could be assigned to asymmetricand symmetric-C02 stretching modes of bridgedcarboxylates.

Therefore, during ethanol oxidation on PdlAh03,NiO/Ah03 and PdINiO/Ah03 catalysts, it was ob-served the formation of ethoxy species and bridgedcarboxylates, which are C02 precursors and mon-odented carboxylate, which are related to acetic acidand ethyl acetate production.

Furthermore, the bands at 1652 and 1413cm-1 werecharacteristic of palladium since their intensity wasvery low on the nickel based catalyst. It means thatthe decrease of the intensity of the bands at 1652 and1413 cm-1 on PdINiO/AI203 catalyst is probably dueto the coverage of palladium particles by nickel atoms.

Fig. 5 displays the curves related to the conver-sion of ethanol at different reaction temperatures.NiO/Ah03 and NiOlCe02/Ah03 catalysts showedvery low activity. These systems were not active at473 K whereas the ethanol conversion was almostcomplete on the Pd based catalysts at the same tem-perature.Ni addition to Pd/Ah03 and PdlCe02/AI203 cat-

alysts strongly decreased their activity. Andersenet al. [7] reported the same behavior on three-waycatalysts in the presence of nickel. According to theauthors, the catalyst deactivation under redox (cycledreducing/oxidizing) aging was due to the formationof Pd-Ni alloy. They suggested that the catalyst de-activation is inhibited by minimizing the interactionbetween the TWC and nickel compound. In our work,TPR analysis showed that palladium addition pro-moted the nickel oxide reduction, which indicated thepresence of a strong interaction between both metals.Under the slightly oxidizing conditions of the catalytictest, this interaction could be destroyed and a strongsegregation of one of the components at the surfacecould take place. In fact, the IR analysis revealed thecoverage of metallic palladium particles by nickel ox-ide, which were not active. This could be responsiblefor the decrease of the ethanol conversion observedon the bimetallic catalyst. This is also confirmed bythe catalytic behavior of the Pd/ Ah03 +NiO /Ah03

---*- Pd--T-PdNi_____ Pd+Ni

~Ni-D-PdNiCee .commercial*PdCe /.... *

--0-NiCe ~~ ~: x

*~ ~. . i _~ 0 ----------n ~. _ x-~--_~~--x

. 60'"~c 40ou

480temperature I K

physical mixture. In this case, the physical mixtureexhibited the same activity than the Pdl Al203 cat-alyst, since there was no interaction between bothmetals. Therefore, in order to minimize the negativeeffect of nickel addition to palladium based catalystson ethanol oxidation reaction, it is important to inhibitthe interaction between palladium and nickel.

Finally, the commercial catalyst showed the sameresults as PdINiO/Ce02/Ab03 catalysts. This resultsuggested that the commercial catalyst could be wellrepresented by the PdINiO/Ce021 Al203 model cata-lysts.

The main products of ethanol oxidation were ac-etaldehyde, acetic acid, carbon oxides and ethyl ac-etate, as it is shown in Figs. 6 and 7. It is worth to

o350

Fig. 6. Selectivities on the ethanol oxidation as a function oftemperature on Pd/Ab03 catalyst. (+) Acctaldehyde; (0) aceticacid; (x) C02; (6) ethyl acetate. Selectivity is defined as the ratiobetwccn thc amount of cthanol convert cd to a product and thereacted amount of ethanol.

stress that the products of partial oxidation are onlyobserved at conversion levels of ethanol below 100%.The curves clearly indicated that acetaldehyde was theprimary product; which was subsequently oxidized toacetic acid and carbon oxides. The reaction betweenacetaldehyde and ethoxy species might produce ethylacetate. In accordance with [3 11, ethanol oxidationis represented by a system of parallel and series re-actions. The presence of Ni shifted all the reactionsystem towards high temperature (Fig. 7). This resultagrees with the decrease of activity shown in Fig. 6.Moreover, the presence of Ni decreased the selectiv-ity towards ethyl acetate, which is probably due to themodification of the acid and basic properties of thesupport.

o400 450

temperature I K

Fig. 7. Sclccti\ities on the ethanol oxidation as a function oftemperature on Pd/NiO/Ab03 catalyst. (+) Acetaldehyde; (0)acetic acid: (x) C02; (/\) ethyl acetate.

In order to study the role of nickel oxide onethanol oxidation, several model catalysts were pre-pared: Pd/Ab03, NiOIAb03, Ce02IAb03, PdlCe02IAb03, PdlNiOIAb03, PdlNiOICe02IAb03,Pd/Ab03 + NiO/Al203 physical mixture. A com-mercial catalyst was also studied.

TPR and OSC measurements revealed that pal-ladium addition strongly promoted the reduction ofcerium oxide and nickel oxide. This effect was moreimportant on PdINiOlAb03 catalyst, suggesting thepresence of a strong interaction between palladiumand nickel.

Pd/Ab03 and Pd/Ce021Ab03 catalysts exhibitedpractically the same catalytic activity. On the otherhand, the presence of nickel decreased the ethanolconversion. Under the slightly oxidizing reaction con-ditions, the interaction between both metals was de-stroyed. The IR analyses showed evidences of a sur-face segregation of nickel oxide, which were not ac-tive. This could explain the low activity of the nickelbased bimetallic catalysts. In order to minimize thenegative effect of nickel addition to palladium basedcatalysts on ethanol oxidation reaction, it is impor-tant to inhibit the interaction between palladium andnickel.

The ethanol oxidation produced mainly acetalde-hyde, acetic acid, carbon oxides and ethyl acetate. Theaddition of nickel shifted the formation of these prod-ucts towards higher temperature due to the decreaseof activity.

A commercial catalyst was also tested and com-pared to the model catalysts. The commercial cat-alyst presented catalytic activity similar to thePdINiOlCe021Al203 catalyst. This result suggestedthat the commercial catalyst could be well representedby this model catalyst.

Marcelo C. Durao and Marcelo S. Batista wouldlike to thank CNPq for financial support.

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