Simultaneous removal of ethanol,acetaldehyde and nitrogen oxides over V-Pd/γ-Al2O3-TiO2 catalyst

Availableonlineatwww.sciencedirect.comJoumal ofScience DirectNatural GasChemistryELSEVIERJournal of Natural Gas Chemistry 20(2011)1679172Simultaneous removal of ethanol, acetaldehyde and nitrogenoxides over v-Pd/y-Al2O3-TiO2 catalystZhe Li, Jing Wang, Kai He, Xia An, Wei huang, Kechang XieKey Laboratory of Coal Science and Technology of Ministry of Education and Shanxi Province,Taiyuan University of Technology Taiyuan 030024, Shan xi, ChinaManuscript received August 17, 2010: revised November 5, 2010 1abstractV-Pd/y-Al2O3-TiOz catalysts with different vanadium contents were prepared by a combined sol-gel and impregnation method. X-rayffraction(XRD), N2 adsorption-desorption(BET), X-ray photoelectron spectroscopy(XPS)and catalytic removal of ethanol, acetaldehydeand nitrogen oxides at low temperature(<300C) were used to assess the properties of the catalysts. The results showed that the sampleth 1wt%osimultaneous removal of ethanol, acetaldehyde and nitrogen oxides. Theconversions of ethanol, acetaldehyde and nitrogen ofdes at 24.4% and 98.7%, respectively. V-Pd/y-Al2O3-TiO2 catalystwith I wt% vanadium showed the largest surfacedium oxide on the catalyst surface, and possessed a largerole fraction of V+t species and unique PdO specieattributed to the strong synergistic effect among palladivanadium and the carriers. The higher activityrelated td the V4+ and Pd2+ species on the surface, whicmight be favorable for the formation of active s esV-Pd/-y-Al2O3-TiO2; simultaneous removal; ethanol acetalde1. Introductiontion. Less acetaldehyde were also produced over the noblemetal catalyst [8]. Petkovic et al. [9] have studied the metalEthanol as a promising additive or substitute for gaso- oxide-supported platinum catalysts for ethanol oxidation achas attracted considerable attention due to the advantages tivity, and they found that Pt nanoparticles trap and accumuof octane enhancement and reduction of carbon monoxide late oxygen at their surface and perimeter sites play the rolefrom exhaust emissions. However, some undesirable prod- of sites where ethanol molecules and their partially oxidizeucts formed by partial oxidization in complete oxidation of derivatives burn and form the final products. Avgouropoethanol,such as unburned ethanol and acetaldehyde [1,2], can et al. [10] have also studied the catalytic performance of alkalead to severe environment and health problems, and they (K and Nat )-promoted Pt/Al2 O3 catalysts for the completehave been recognized as major contributions to pollution and oxidation of ethanol, and found that adding alkalis into aluthe formation of photochemical smog. Moreover, on a stan- mina could neutralize the acidic sites of alumina and suppressdard three-way catalysts(TWCs ), the conversion of unburned the formation of diethyl ether and ethylene. Lin et al. [ll]ethanol is low [3] because both ethanol and acetaldehyde are have observed that Ceo. 75Zr0 25 02 catalyst containing a modhighly resistant to oxidation [4]erate content of Pdo can enhance the catalytic oxidation ofTherefore, many studies were performed for complete ox- ethanol effectively, and ethanol can be subsequently oxidizedidation of ethanol over catalysts regarding the emissions ceto COz following the formation of acetaldehyde, acetic acid,trol from ethanol-fuelled vehicles. According to mccabe et ethyl acetate and ethylene. Sheng et al. [12] have studied theal.[5]and Yao [6], in general, PU/Al2 O3 catalyst is more ac- surface reaction of ethanol on Au/CeO2 catalyst; They foundtive than base metal oxide catalysts. Rajesh et al. [7] have that the formation of hydrocarbon-products with a distributionfound that CuO/Al O3 is the most active base metal oxide was depended on the reaction temperature, and acetaldehydecatalyst for the complete oxidation of ethanol. However, cop- was the main reaction product at 573 Ker addition on y-Al2O3 enhanced the acetaldehyde forma-Although the catalytic oxidation of ethanol has beenCorrespondingauthor.Tel:0351-6018564:Fax:0351-6018564:E-mail:lizhe@tyut.edu.cnhe work was supported by the National Natural Science Foundation of China(No. 210中国煤化工 cience foundation(No.2009011011-3)CNMHGCopyright(2011, Dalian Institute of Chemical Physics, Chinese Academy of Sciences. All rights reservedoi:10.1016/S1003-9953(10601594Zhe Li et al /Journal of Natural Gas Chemistry VoL. 20 No. 2 201Iwidely studied, to our knowledge, there are no reports so far powder X-ray Rigaku diffractometer(Japan, Rigaku) opfor focusing on such an area, in which ethanol, acetaldehyde erated at 40kV and 100 mA with a Cu Ka radiationd nitrogen oxides can be catalytically and simultaneously (=0.154056 nm), and 20 scanning was performed from 10emoved from the exhaust emission of alcoholic fuel vehicles. to 85 with a step size of 0.01In our previous report, vanadium based catalyst supported onn-Al2O3-TiO2 composite has been found to possess a better 2.3.2. BET specif ic surface areaperformance for the complete oxidation of ethanol under asuitable temperature [13]The present work mainly focused on simultaneous reSurface area of catalysts was calculated on Italy Sorpmoval of ethanol, acetaldehyde and NO r over V-Pd/y-A1203- tomatic 1990 automatic physical adsorption instrument by theTiO2 catalysts. The bulk-phase structure and surface compoBET method; nitrogen adsorption isotherms were obtained atsitions of this kind of catalysts are also studied using XRD, 77K, and the samples were degassed at 573K in vacuum forN2 adsorption-desorption and XPS techniquesat least 3 h prior to analysis2. Experimental2.3.3. X-ray photoelectron spectroscopy (XPS)2.1. Catalyst preparationChemical states of Pd and V atoms in the catalyst surfacewere investigated by the X-ray photoelectron spectroscopy onThere are two steps for catalyst preparation. The first the ESCALAB250 multi-purposeelectronic energy spectromoneis to form a composite oxide support, 7-Al2O3-TiO2, us- eters(Al Ka radiation). The XPS data were calibrateing a sol-gel method. The aluminum and titanium sols were on the standard binding energy of C Is(284.6ev/d basedprepared separately, and then mixed them together to obtain-Al2O3-TiO2 [23 in which the content of titanium dioxidewas about 95%. The second step is to prepare the catalyst3. Results and discussionv-Pd/y-Al2O3-TiO2, which contains I wt% Pd and differentvanadium contents. To do this, -Al2O3-TiO2 was impreg- 3. 1. Catalytic removal of ethanol and NOxnated with the aqueous solution of PdCl2 using an incipientwetness technique. The impregnates were dried at 80C in aCatalytic activities of v-Pd/y-Al2O3-T1O2 catalysts werewater bath and at 110C in oven for 24 h, and then calcined at tested in ethanol oxidation and reduction of NOx.Figure550C in air for 5 h; the resulting catalyst was designatedPd/ay-Al2O3-T1O2. Using the same technique, Pd/y-Al2O3shows the effect of temperature on the ethanol conversion overV-Pd/ -Al2O3-TiO2 catalysts with different vanadium conTiO2 was impregnated with the aqueous solution of v2O5nts. From Figure 1, it can be seen that the pd/y-Al2O3-tand the V-Pd/y-Al2O3-TiO2 catalysts with different v con- catalyst has a better catalytic activity, but there are many untents were obtained and designed as n%V-Pd/y-Al2O3-TiOwhere, n% denotes the weight percentage of vwanted products formed by partial oxidization during theaction process, for example acetaldehyde [14]. This agrees2. 2. Catalyst evaluationwith the result reported by noronha et al. [15]. When a suitable amount of vanadium was loaded on the Pd/y-Al2O3-T10The measurement of catalytic activityied outsample, the catalytic activity in ethanol oxidation is increasedremarkably. With a lower content(<1%)of vanadium andatmospheric pressure. The feed gas consisting of 0.3 vol%C2H5OH or CH3 CHO, 300 ppm NO, 3%O2, and balancing vanadium. When the content of vanadium is about I wt%oN2 was supplied to the catalyst bed through mass flow con. the conversion of ethanol reaches the maximum value. HowThe total gas flow rate was 300 mL/minIand 0.30 g catalystever, when the content of vanadium is higher than I wt%was used. Ethanol or acetaldehyde was fed into the reactor bythe ethanol conversion reduces with increasing the vanadiumpassing N2 with a bubble system at 20C. The compositions content. This indicates that an appropriate content of vana-of ethanol and acetaldehyde in the feed gas and the effluent dlum can promote the catalytic performance for oxidation ofgas were analyzed using an online gas chromatograph withethanolFId detector; Nitrogen oxides(NO, NO2) and O2 were deIt can be noticed that acetaldehyde as reaction intermetected by Combustion Gas Analyzer(KM9006 Quintox, Kanediate in the oxidation of ethanol is reduced distinctly overInternational limited)V-Pd/y-Al2O3-T1O2 catalyst(see Figure 2). This illustratesthat the addition of suitable amount of vanadium can improve2.3. Characterizationthe catalytic property for total oxidation of ethanol. Once thevanadium content中国煤化工 Sion of ethanol2.3. 1. X-ray diffraction (XRD)CNMHGhis may be resulted from the aceunUI wU mull vanadium speciesXRD patterns were obtained using a D/max 2500 on the surface and the reduction of active site numbJournal of Natural Gas Chemistry VoL. 20 No. 2 201IPd/y-Al2O3-TiO2 catalyst has the lowest catalytic activity.the conversion of NOr increases slowly with increasing thecontent of vanadium(<1%)at a temperature below 250Cand reaches 82% at 250C. Once the temperature is aboveion of NOr on these catalysts droppedslightly, and this could be related to a complete combustionof ethanol as a reductant of NOx in high temperature-O-Pd/y-ALO, - TiO▲0.4%V-P/r-Al-TiO-V-1%V-Pd/Y-AL, O, -TiOC-3%V-Pd/y-AL,O -TiO-Pd/y-AL,O, -TiO,(5%V-Pd/y-AL,O -TiO,-8%V-Pd/y-AL,O - TiO己0.4%V-Pd/y-AL, O, -TiO0 LedA50100150200250300350400450500550会60-5% V-Pd/r-AL, O-TiOFif temperature onthanol conversion over 1%V/yAl2 O3-T1ly-Al2O3-TiOz andAl O3-TiO 2 catalysts withdifferen050e 1%V-Pd/y-AL,O, -TiO,A Pd/y-ALO -TiOFigure 3. Effect of temperature on acetaldehyde conversion overI%Vhy-AlO3-T1O2, Pd/y-Al2O3-T1O2 and V-Pd/ay-Al2 O3-TiO2 catalystswith different vanadium contents1802000 I%V-Pd/y-AL, O-TiO,overf Pd/y-Al2O3-TiO2 and 1%v-pd/y-Al O3-TiO. Reaction condition is the8289z1%V-Pd/y-AL, O, -,-3%V-Pd/r-AL, O, -TiO,r5%V-Pd/y-AL, O -TiOWhereas the catalytic performance of 1%v1y-Al2O-F8%v-Pd/ -AL, O,-TiOT1O2(0% Pd)is poor for the oxidation of ethanol and acPd/r-AL O,TiOetaldehyde at low temperature (see Figures I and 3), and1001502002503003504004505005501%V-Pd/y-Al2O3-T102 catalyst not only gives the best perTemperature℃)formance among the catalysts with different vanadium con- Figure 4. Effect of temperature on the NO conversion in the presence oftents, but also is more active than single Pd/7y-Al2O3-TiO2 and ethanol over V-Pd/ -Al2O3-TiO2 catalysts with different vanadium contentsAl2O3-TiO2. This suggests that there is a synergisticeffeelbetween V and Pd species on the surfaceThe catalytic activity of V-Pd/y-Al2O3-TiO2 for the re- 3.2. Catalytic removal of acetaldehyde and NOxmoval of NOr in the presence of ethanol is presented in Figure4. It can be seen that for all catalysts, the conversion of nO xConsidering the importance of acetaldehyde for catalyticincreases sharply with increasing temperature from 100C to removal of NOr, it is interesting to understand the co-reaction250C. When the temperature is around 250C, the conver- of acetaldehyde, O2 and NOx. The catalytic activity of vsion of NOr reaches the maximal value; however, once the Pd/ay-Al2O3-T1O2 for simultaneous removal of acetaldehydetemperature is higher than 250C, the conversion declines and NO in O2 is presented in Figure 5. Compared with theghtly. It is worth to note that catalyst with l wt% vana- catalytic evaluation for the conversion of ethanol and nOzduma hibits a notably higher catalytic activity comparing shown in Figures and 4. the catal ytic activity of vpdnwith bther vanadium content samples for the catalytic reduction of no. as the same as showed in Figure 1 which leads The conversionCNMHG50%at225°eperat ur eat urelbo D)170Zhe Li et al /Journal of Natural Gas Chemistry VoL. 20 No. 2 201Ifor catalytic oxidation of acetaldehyde and ethanol could benttributed to the difficult decomposition of-CHO, because-CHO in acetaldehyde is more stable than -oH in ethanolcatalytic behavior for the reduction of NO in the presence of 3acetaldehyde is similar to that in the presence of ethanol asshown in Figure 3. The conversion of NOr also starts to decrease slightly from the maximum point at a high temperatureabove 250C. It is worthwhile to notice that ethanol is exEthanoltremely effective for NOx reduction [16, 17]. Thus, the resultsAcetaldehydeobtained from Figure 4 and Figure 5 suggest that acetaldehyde has a similar reaction process with ethanol for catalyticreduction of NOx, and acetaldehyde is the primary intermediTemperature(℃)ate product in oxidation of ethanol [ 15, 226. Catalytic performance of simultaneous removal of ethanol, ac-de and NOx over 1%V-Pd/y-Al2O3-TiO2 catalyst3.4. X-ray diffraction(XRD)The Xrd patterns of all fresh V-Pd/ay-Al2O3-TiO2 catalysts with different vanadium contents are presented in Fig-入ure 7. It can be seen that no obvious PdO or Pd signals areobserved due to the low Pd content for all the catalysts. Allsamples show typical diffraction peaks for TiO2 at a 20 of2054.44°and63Acetaldehydconsistent with the standard diffraction peaks of anatase. Noseparate y-Al2O3 phase can be detected, indicating that thephase. Both patterns of (1)and (2) only present the phasesFigure 5. Effect of temperature on theof acetaldehyde and NOz of anatase TiO whereas with increasing vanadium contentover 1%v-Pd/:-Al2O3-T1O2 catalyst(lwt%), some weakly crystalline vanadium pentoxide appears, which can be seen from XRD patterns of (3),(4)and(5). There are no crystalline features for vanadium ox-3.3. Catalytic removal of ethanol, acetaldehyde, and NOr siide observed from(1)and(2)patterns, and this is an evidencemultaneouslythat vanadia presents in the monolayer dispersion state on thesurface of v-Pd/y-Al2O3-TiO2 catalyst. It is worth to mentionFigure 6 shows the dependence of the conversions on temperature for the simultaneous removal of ethanol, acetaldehyde and NOr over 1%V-Pd/y-Al2O3-T1Oz catalyst. Comparison of the catalytic behaviors of ethanol and acetaldehydeo TiO,indicates that they have similar reaction trend in a temperaturerange of 100-550C, except for a higher catalytic activity inethanol oxidation. In the case of ethanol, the complete oxi-ion can be achieved at 225C. which is about 100-150Clower than that for the complete oxidation of acetaldehydeThis could be taken into account that acetaldehyde is one ofthe main intermediate products during oxidation of ethanoland then they continue to react with oxygen in the feed toform carbon dioxides. moreover it can be observed that themaximal conversion of NOr in the presence of ethanol andacetaldehyde takes place at 250C. However, as the temper-ature is raised, NOr conversion decreases gradually, whereasethanol and acetaldehyde are still keep their high conversionsThis means that high temperature has an influence on the con中国煤化工version of NOr, nevertheless, the catalytic combustions of Figure 7. XRD patter-with different vana-CNMHGy-A1203-TiO, (3)ethanol and acetaldehyde at high temperature certainly lead 3%V-Pd/-y-A1203-TiO2, (4)5c v-Pd--A1203-TiOto a competition witit2 @reduction of3 040 T102506080Journal of Natural Gas Chemistry VoL. 20 No. 2 201Ihere that vanadium plays an important role in improving the reduction of V+ through the synergistic effect of vanadiumdispersion of V and Pd species on the surface, further pro- oxide and Pd species oxides on y-Al2O3-TiO2, and the V++moting the synergistic effect among palladium, vanadium and species on the surface are beneficial to improving the catalytiche carriers. Once adding too much vanadium, accumulation activity [13]could occur on the surface and thus the active sites were rehe photoelectron spectra of Pd 3ds /2 of the samples areducedshown in Figure 9. The data indicate that the binding enerTable I presents the surface area of representative sam- gies for Pd 3d5/2 are around 33670eV and 337.75eV forples calcined at 550C, it has been found that the catalysts the samples, except for 1%v-Pa/y-Al2O3-TiO2. These resultswith lower contents of vanadium can get larger BET surface are in agreement with those reported in literatures for Pd+inarea than those with higher contents, and sample with I wt% PdO and Pd- in Pdo2 [19, 20]. However, there is only bindvanadium has the largest value. This can be attributed to the ing energy of 336. 61 eV corresponding to Pdo in the samplemonolayer dispersion of vanadium, which is favorable to pro- with I wt% vanadium content, indicating that adding aand the carriers, and to further promoting the formation of acTable 1. N2-adsorption characteristics of samples calcined at 550C0. 1%V-Pd/y-Al2 O3-Ti00. 4%V-Pd/y-Al2 O3-TiO29.83%V-Pd/ -TiO1%V-Pd/y-Al,O -TiO,入3.5. X-ray photoelectron spectroscopy (XPSIn order to understand the influence of vanadium content0.4%V-Pd/y-AL,O -TiOon the catalytic activity of v-Pd/y-Al2O3-T102, the chemio cal states of vanadium atoms on the surface of the represen-tative samplesyestigated by XPs. Table 2 presents512514516518520522524526528the binding energies of the V 2p3/2 lines and the mole frac-Binding energy (ev)tion calculated from XPS measurement and chemical anal- Figure8. XPS spectra of V 2p on v-Pd/-y-AI2O3-TiO2 catalysts with differ-Moreover, Figure 8 shows the photoelectron spectra ent vanadium contentsof V-Pd/y-Al2O3-TiO2 Only two peaks centered at 5175eVand 516.5eV, corresponding to the presence of v5+ and V4+[18], can be detected for all the samples. The values observed from V 2p3/2 line reveal that the catalyst surface withPdofully oxidized state of vanadium is predominant. Sample with0.4 wt% vanadium presents about 43. 82%V++ species,whV4+ on the catalyst with 1 wt% vanadium increases to 75%However, the mole fraction corresponding to V4+ speciesPdodrops to 57. 21% and 36. 24%o for the samples with 3 wt% and5 wt% vanadium, respectively, while Vs+ presented the maincontribution gradually. from Table 2, figure 8 and the best re-ult obtained from Iwt% vanadium sample, we can concludePdothat the formation of V4t species is due to the incompleteTable 2. Peak fitting data obtained from XPS spectra ofV-Pd/y-AlzO3-TiO2 with different vanadium contentsSpeciesBinding FWHM MolePdO→Pdo0.4%VP/y-A2O3TiO2V+(v2p3/2)516.47183438V+(2p3/2)517.561.7756.131% V-Pd/7y-Al2O3TiO2V4(V2py2)516312.32Vs+(v2p3y/2)517491.713323343%vPd/-A2O3TO2V+N2p3/2)516.221.735721中国煤化工V5+(2p3/2)517.401.8142Figure 9. XFCNMHGiOz catalysts with5%vPd/y-A2O3TO2V4+(V2p3/2)5166015936.24different vanadium contents. (1)0.4%v-Pd/hy-Al2O3-TiO2,(2)1 %v-pd/2.2763.76Al2O3-TiO2, (3)3%V-Pd/y-Al2 O3-TiO2, (4)5%V-Pd/-y-Al2O3-TiO2332336338340342Bi ndi ng ener gy( ev172Zhe Li et al /Journal of Natural Gas Chemistry VoL. 20 No. 2 201Isuitable amount of vanadium into the catalyst can promote Pd123(1-3):29species to exist in the form of PdO rather than PdO2; thus[2] He B Q, Wang J X, Hao J M, Yan X G, Xiao J H Atmos Environ,in be deduced that PdO species is more active than PdO2 for2003,37(7):949the oxidation of ethanol and acetaldehyde and the reduction [3] Burgi t, wirz r, Baiker A / Phys Chem b, 2003, 107: 6774of nitrogen oxides according to the result of evaluation(FiS SG, Samaras D P, Philippopoulos C J Atmos Envures I and 4). Persson et al. [21] have also found that pdoirOn,2001,35(26:4399was active for ethanol oxidation over Pd/Al2O3 catalyst.[5] McCabe R W, Mitchell P J Ind Eng Chem Prod Res Dev, 198423(2):196[6 Yao Y FY Ind Eng Chem Process Des Dev, 1984, 23(1): 604. 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An X Ren PJ, Huang W, xie K C J/ Nat Gas Chem, 200918(3):379persion of palladium and vanadium species over the support, [14] Li Z, Jiang S H, Quan Y H, Xu L, Huang W J Fuel Chem Techwhich is resulted from the strong synergistic effect among pal-l(Nanliao huaxue Xuebao ), 2009, 37(1): 71ium, vanadium and the carriers. XPS results showed that [15] Noronha F B, Durao M C, Batista M S. Catal Today, 2003vanadium oxides on the catalyst surfacand V2O5, palladium presented in the oxidized state of Pdo or [16] Sumiya S, Saito M, He H, Feng Q C, Takezawa N,Yoshida KPdO2. 1%V-Pd/y-Al2O3-TiO2 catalyst showed a larger moleCatal Let,1998,50(1-2):87the sur- [17 He H, Yu Y B Catal Today, 2005, 100: 37ace, which can be attributed to the strong synergistic effect [18] Zhao H, Bennici s, Shen J, Auroux A Appl Catal A, 2009, 356among palladium, vanadium and y-Al2O3-T1O2. 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