Effect of Lanthanum on Methanol Fuel Exhaust Deep Oxidation over Pall adium Catalyst

JOURNAL OF RARE EARTHSVol.2I ,No.1 , Feb. 2003 ,p. 51Effect of Lanthanum on Methanol Fuel Exhaust DeepOxidation over Palladium CatalystWang Xingyi(王幸宜)* , Wan Ying(万颖 ), Lu Guanzhong(卢冠忠)( Institule of Industrial Catalysis , East China University of Science and Technology , Shanghai 200237 , China )Abstract : The performance of deep oxidation of methanol on supported Pd catalyst was examined by a chromatograph-mi-cro-reactor . The results show that the addition of La into Y-Al2O3 support can affect greatly the performance of the Pd cata-lyst. In the absence of CO ,La can decrease the content of oxygen-containing intermediate , although La can not lower thelight-off temperature of methanol oxidation. In the presence of CO , La can lower the light- off temperature , decrease theamount of CO adsorption，and weaken evidently" CO inhibition" to the oxidation of methanol. By XPS technique ,it isshown that La modifies the electronic structure of Pd , which attributes to the modifications of the catalytic performance .Key words :supported palladium catalyst ; methanol oxidation ; lanthanum ; rare earthsCLC number : 0643.3Document code : AArticle ID : 1002- 0721( 2003 )1- 0051 - 04Being its good oxidizing performance ,Pd ,as anous solution at pH 2~ 3 ,aging for 24 h ,drying at 100active component , has been used widely for catalyticC for 12 h and calcining for4 h at 500 C. The vari-combustion，such as CO oxidation ，automobile ex-ous supports ,20 ~ 40 mesh particles , were impregnat-haust purification and so on. In the purification ofed with PdCl2 aqueous solution. Two catalyst samplesmethanol automobile exhaust , Pd possesses good activ-were obtained :0. 1% ( mass fraction )Pd/Al2O3 andity in converting methanol at low temperature , but its0.1% ( mass fraction ) Pd/5% La-Al20s( weight perselectivity to CO2 is poorl 1-61. In the presence of CO ,cent ofLa in Al ). The catalyst samples were reducedthe activity of methanol oxidation on Pd catalysts canwith 10% H2+ 90% N2 mixed gas( 20 mt min-1 ) forbe inhibited greatly31. Reports have shown that both3 h at 250 9C before catalytic testing.CO inhibition" can be promoted and the selectivity to1.2 Catalytic testingCO2 can be enhanced through the addition of other ele-ment56], for example , Ag4]. La has been used asCatalytic tests were performed in a chromato-additives to improve effectively the performances of Pdgraph -micro-reactor of中1.2 cm X 40 cm，at a con-automobile catalysts7I , both in activity and heat sta-stant space velocity of 15 ,000 h -1 with 0.5 g catalyst.bility , but has not been applied in methanol automo-For CH3OH + 02 reaction ,the composition of the feed-bile catalysts. It should be noted that La could modifystream was 0. 74% ( molar fraction ) CH3OH ,4. 0%the performance of metal catalysts in the area of( molar fraction )02in N2 ;for CH3OH + O2+ CO reac-catalytic combustiornt8J and promote the activity of Agtion, the feedstream was 0. 74% ( molar fraction )methanol automobile catalysts 9,10]. In this paper ,LaCH3OH ,4. 0% ( molar fraction )O2 and 0. 3% ( mass .was doped into Y-Al2O3 support , and the valence of Pdfraction )CO in N2. The analyses of the gas mixture aton catalyst surface was tested which was correlatedthe inlet and at the outlet of reactor were performed bywith the activity and selectivity of CH3OH oxidation .gas chromatography. For CH30H , HCHO , CH;OOHand CH3OCH3 ,a column flled with 403 organic sup-1 Experimentalport( coated with sorbitol ) was used with FID detec-tor. And for O2 ,N2 , CO and CO2 , two columns were1.1 Catalystsemployed in parallel connected from , and one filledSupports were prepared by impregnating pse-with中国煤化工nother fled with sliconduoboehmite in La nitrate solutions or in acetatic aque-gelYHCNMHGetector.Received date : 2001 - 06- 18 ;revised date : 2002 -08 - 28Foundation item : Project supported by Shanghai Academic Foundation for Young Teacher in Advanced SchoolsBiography,Vasg Xingyi( 1958 - ), Female , ProfessorCorresponding" Author ( E-mail : wangxy @ ecust . edu. cn )52JOURNAL OF RARE EARTHS , Vol.2l ,No. 1 , Feb .20031.3 BET analysis2.2 CH;OH + CO + O2 reactionThe BET surface area data were obtained orMcCab et al .[4] have found that , in the presenceTRISTAR 3000 using N2 as analysis adsorptive atof CO , methanol conversion could be inhibited , and- 195.8 C with warm free space 8. 8558 cm3 andthis phenomenonis called' CO intervention" effect. Incold free space 23. 0015 cm3.this section ,0.3% CO was added to the reactant feedto examine the effects of CO on the activity of Pd cata-1.4 XPS analysislysts. The results are shown in Fig.2. On Pd/Al-O ,The XPS data were obtained on a Kratos XSAMCH3OH conversion is lowered to some extent in the800 using Al Ka radiation at 65 W and 40 eV pass en-presence of CO and the conversion curve shifted toergy. The XPS binding energies were referenced to thehigh temperature , with Tso increasing from 75 C( inadventitious C1s level at 284. 8 eV.the absence of CO )to 175 9C , T100 from 110 to 240C. For Pd/La-Al-0 , the" CO inhibition" effeet still2 Results and Discussionexists at temperature lower than 110 C , and Tso in-creases from 50 C( in the absence of CO )to 100 9C2.1 CH;OH + O2 reactionwhile if the reaction temperature is raised to higherTiwo kinds of Pd catalysts , supported on Al2O3than 110 C , this”CO inhibition" effect can be de-( BET surface area 272 m2- g-1 , and 5% La-Al2O3 .creased greatly. Tso on Pd/La-Al-O is 75 9C lower( 258 m2 g-1 ) were designated as AI-O and La-Al-Othan one on Pd/Al-O. On the other hand , on Pd/Al-respectively , and tested. The variation of methanolO there is no methyl-formate in the reaction products ,conversions and the selectivity to CO2 as function of thebut formaldehyde and methyl ether still occurred ,reaction temperature are showed in Fig. l(a). It can beshowing that the distribution of oxygenic intermediatesseen that , the activity on Pd/AI-O is high ,and its Tsoin the presence of CO can be changed( Fig.2). Withand T1oo( Tso and T1oo reaction temperatures corre-no oxygenic intermediates appeared on Pd/La-Al-O.sponding to 50% and 100% methanol conversion , re-During the oxidation of methanol , the conversion ofspectively )are 75 and 110 C respectively , while TsoCO was also tested and the result is shown in Fig. 2and T 100 on Pd/La-Al-O were 60 and 180 C respec-( a ). The activity of oxidation of CO on Pd/La-Al-O istively. Additionally , several kinds of oxygenic interme-better than one on Pd/Al-O. For the former , Tso anddiates were observed during methanol oxidation on Pd/Tloowere 150 and 175 C respectively , are obviouslyAl-O Fig. I( b ), among which , methyl-formate is up tohigher than those of methanol. For the latter , Tso and0.06% and formaldehyde up to 0.016% at low temper-T1oo ,167 and 184 9C respectively , similar to those ofature , while methyl ether up to 0. 032% at 285 9C.methanol. From the above results , we concluded thatHowever , no oxygenic intermnediates was produced onthe addition of La into supported Pd catalyst can pro-Pd/La-Al-O in the reaction temperature range. It canmote the selectivity of methanol oxidation to CO2 , de-be concluded that La added in the support could pro-crease the emission of intermediates ，and abut the .mote the selectivity to carbon dioxide of methanol oxi-CO inhibition" effect.dation , although the activity of Pd/A1-O is better.00 r. (a)0.06I (bp -◆Pd/Al-O(HCOOCH)+ Pd/AI-O(HCHO)50▲PdAI-O(CHzOCH)10-◆-Pd/La-AI-O(CHzOH)|一Pb-Al-O(CH2OH)20￥- Pd/A1-O(CO2)号:*-Pd/La-AI-O(CO3)中国煤化工〉200 300 40YHCNMHG300400θ/CFig.1 Effect of La on deep oxidation of CH30H( 0.74% CH;0H in feed gas ,S V= 15000h-1)(a)CH3OH convesion and seletivity ;( b) Amount of oxygen-containing intermediatesWang X Y etal. Effect of La on Methanol Fuel Exhaust Deep Oxidation over Pd Catalyst530.05100(a)0.04▲Pd/AI-O(CHjOCH;)A Pd/AI-O(HCHO)0.03PdLA-Al-Q(CHzOH%)|8 40▲Pd/AI-O(CH2OH9%)0.02Pd/LaAI-O(CO%)5 20Pd/AI-O (CO%)0.01) 10020250 30030000o/CθrcFig.2 Effect of C0 on deep oxidation of CH3OH on Pd/Al-O and Pd/La-Al-0( a )CHzOH conversion and selectivity ;( b ) Amount of oxygen- .containing intermediatesIn addition to peak at 334.8 eV , however , there2.3 XPS researchoccurred a peak of Pd3d/2at 336.1 eV for Pd/La-Al-XPS was employed to reveal the changes in the0 after the oxidation , showing Pd in oxidized state .electronic structure of catalyst might be inducedThe result indicates that there are interactions betweenthrough Pd-lanthana interaction. Fig. 3 shows Pd3dLa2O3 and Pd in the presence of reaction feed. TheXPS spectra for the Pd on the different supports afterouter Pd electron density and the inner electron bind-pretreatment in 3 ways : caleination in air at 500 Cing energy may both increase . Additionally , the basic-( noted air ), reduction with hydrogen at 250 C ( H2 )ity of lanthana makes Pd more electropositive and easi-and methanol oxidation ( reaction feed ). The peakser to be oxidized , and the binding strength betweenobserved for the Pd3ds/2 and 3d3/2 levels were given.the adsorbed methanol species and the palladium sur-The peak of the Pd3ds/2 binding energy for Pd/AI-Oface may be weaken.appeared at 336. 1 eV , which agrees with the peakmaximum observed for PdO9J. Following the reduc-2.4 CO adsorptiontion with hydrogen , the binding energy of Pd 3ds/2The amounts of CO chemisorption on the Pd/AI-peak shifted to 334.4 eV ,which is in good agreementO and Pd/La-AI-O pretreated in the reaction feed atwith the binding energy reported for metallic palladium140 C were 1.89 and 0.14 μrmol g-' ,respectively ,of 335 eV[12]. This shows that Pd2 + might be reducedindicating that the amount of CO chemisorption usinginto Pd. After the methanol oxidation , the Pd3ds/2the Pd/La-Al-O catalyst is much lower than that onbinding energy increases slightly to 334.9 eV , whichthe Pd/Al-O catalyst. This is related to the highermeans that the chemical valence of Pd became oxi-electropositivity and partial oxidized state of Pd on Pd/dized. For Pd/La-Al-0 ,the Pd3ds/2 binding energy ofLa-Al-O support. Because of the strong adsorption ofsamples( air and H2 ) are 336.1 and 334.3 eV re-CO , the adsorption of methanol or oxygen on Pd/Al-Ospectively. The positions of these peaks were nearly i-sample may be inhibited. If the adsorbing sites weredentical with those observed for similarly treated Pd/avail-Al-O samples .Pd/La-A1-0(b)Pd/A12O3Reaction fedReaction feedHz中国煤化工H2DYHCNM HG AirAir34033330345335E/eVFig.3 XPS spectrum of Pd/Al-O and Pd/La-Al-O catalysts54JOURNAL OF RARE EARTHS , Vol.2l ,No. 1 , Feb .2003(a) Pd/Al203 ;( b)Pd/La-AI-Oable , metha nol and oxygen could be adsorbed , thenvehicle exhaust[P] USP 4673556 , 1987.react with each other readily. The methanol conversion[2] WeCabe R W. Reactions of ethanol and acetaldehydecurves are overlapped with CO oxidation curve( Fig.2over noble metal and metal oxide catalysts[J ] Ind. Eng.Chem. Prod. Res. Dev. ,1984 ,23( 1 ): 196.(a )) , referred to the efect of the strong adsorption of[3] MeCabe R W ,Mithell P. Exhaust-catalyst developmentCO on methanol conversion. On Pd/La-Al-0 , the ad-of methanol fueled vehicles: 1. 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Chem. ，1974 , 46dation of carbon monoxide and unburned fuel in methanol( 1):197.Effect of LaCl3 , PrCl3 on Photophosphorylation of Spinach ChloroplastsPan Dengkui * ,Wang Yuguo ,Zhang Jintong( Shanxi Agricultural University , Taigu 030801 , China )Abstract : The experiment of rare earth( RE ) in potstrongly photoreaction of chloroplast to ( FeCy ) thanand field trials by spraying on leave , seed dressingLa'+ does.and seed soaking has fully proved that the RE ,as aAfter the chloroplast were further treated by 15micro-fertilizer , promotes obviously the growth and de-and 25 pμmot L-1 LaCl3 , ADP/O rate and photosyn-velopment of plant under similar ecological condition .thetic contro( PC ) value increased in different degreeThe efficiency or level of phosphorylation is a decisivein cycle phosphorylation( + PMS ) and cycle photo-factor in infuencing the growth and development ofsynthetic phosphorylation( + FeCy ，+ MV ) underplants. The result shows that the photoreduction activ-50000 lx ilumination. Treating chloroplast with suit-ity of chloroplast in excised leave of spinach on K3Feable concentration of LaCl3 and PrCl3 , the activity of(CN )( FeCy ) increases as the concentration of La3+Mg2+-ATPase and Ca2 +-ATPase rised apparently andand Pr3+ in creasing , the kinetic curve shapes” S"effect of LaCl3 was more distinct than PrCl3. It is sug-and the Hill coefficients of the curve are respectived'中国煤化工enhance lhe polo2.8 and 5.0. The results indicate :( 1 ) Both La3 + andsyntnis is probaly related toPr3+ obviously promote the chloroplast photoreaction ;thes:YHC N M H Gng photosynthetie phos-( 2 )La3+ and Pr3+ may have the same function mecha-phorylation factor( CF1 ) and has nothing to do withnism and function point ;( 3 )Pr+ influences moretransferring electron in photosynthesis .Key words : rare earths ; lanthanum chloride ; praseodymium chloride ; photophosphorylation ; coupling factors(SeeJ. Chin. RE. Soc.( in Chin. ),2003 ,21( 1)77 for full text )