Kuriacose, J. C.

Subrahmanyam, M.

English

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Indl$ Journalof ChemistryVol.*5A.July 1977,pp. 58b-588Behaviour of Oxide CatalystsDuring the Catalysed Reactions cfPropan-2-o1M. SUBRAHMANY AM & J. C. KURIACOSEDepartmentof Chemistry,Indian Institute of Technology,Madras 600036Received 23 October 1976; accepted 2 February 1977Oxidationcatalystsusedin thedehydrogenationf propan-2-o1are deactivatedwith use.A varietyof singleandbinaryoxideshavebeenstudiedto determinethefactorsresponsibleforthis deactivation.Somegeneralizationsfor screeningoxidationcatalystsfor selectivityareindicated.rr'RANSITION metaloxides,pure and mixed,JJ are widely us d in catalyticvapourphase. oxidation1,2. Since the early 1960's therehas,beenmuchinterestin theoxidativedehyclrogene-tiortandammoxidationof mono-olefinsto diolefins,ald~hydesand nitriles3-5. The reactionmechanismof 'the oxidationof olefinssuch as propeneandbutjeneor of mixturesof propeneandammoniaovercat~lystssuch as bismuth molybdenumoxidecor{lbinationsi consideredto be reasonablywellun4erstood.However,a numberof detailsin themechanismremainuncertain. Oneof theimportantquestionsarising in the mechanisticstudies ofthe~ereactionsis the role of latticeoxygenin theoxidation,which in turn dependson the mobilityof the oxideions. The studiesaredifficultbecauseof themanyproductsinvolvedin the reactionsandthe absenceof informationas to the adsorptionequilibria of the various reactantsand rea.ctionprqducts.As a first stepin a resea.rchmeantto understandthe factorscontrollingthe activity, a numberofoxidesof differentelementswhichhavebeenusedmostlyfor oxidationof olefinsweretestedfor thedeCompositionof propan-2-01in orderto correlatethe reactionof propan-2-01to the selectivityof thecatalystfor theoxidationof olefins. The reactionsof ipropan-2-01Onthesecatalystsgive rise to onlya limitednumberof productsunlike the oxidationofo1cfins.Preparation of catalysts- All the chemicalswereofBDH analargradeand usedas received.the following materialswere used as startingmaterials: Nitrateswereusedfor bismuth,cobaltand zirconium,chloridefor antimonv,ammoniummetavanadatefor vanadiumand()xid~sfor tungstenantI molybdenum.Antimonyoxidewaspreparedby first convertingantimonychlorideto hydroxideby precipitationfromanaqueousolutionwithammoniumhydroxide.The hydroxidewasfiltered.washedfreeof chloridewith clistilledwater,driedat 130°and decomposedat 550°for 5 hr.Vanadium pentoxide was preparedby threedifferentmethods:(a)Vanadyloxalatewaspreparedfrom ammoniummetavanadateand it was decorn-p06edto oxideat 5500; (b)vanadicacidwasprecipi-586tatedfrom ammoniummetavanadateby nitric acid,driedandcalcinedat 550°for 5 hr; and (c) ammo-nium metavanac1atewas decomposedto vanadiumpentoxideat 5500in acontinuoustreamofair.Zirconiumdioxidewaspreparedby precipitatingthe hydroxidefrom the nitrate with ammoniumhydroxideand decomposingit at 550°.For the preparationof binary oxidesoneof theoxideswas suspendedin boiling water and theother componentin its hydroxideform addedtothe suspension.The total masswas stirredvigo-rouslyandwas left on a water-bathfor 1 hI' afterwhichit wasfiltered. The residuewasdriedover-nightat 110°3nelcalcinedat 550°for 5 hI'.Reactionswerecarriedout in a flowtypereactorfunctioningat atmosphericpressure.The packingof the reactorandexperimentalprocedurehasbeendescribedin an earlierpaper6. The catalystwasactivatedby heatingit at 450°in a streamof dryair for 20min. The liquid productswereanalysedby gas chromatographyusinga carbowaxcolumnat 75° and the gaseousproductswere analysedusingan Orsat'sapparatus6•ResultsandDiscussionThe results for the reactionof propan-2-01onoxidesof V, ]\10, \V. Co, Ri, Zr, Sb and Sn takensingly or in combinationare presentedin Tables1 and 2. Most of thesecatalystshave attractedconsiderableattentionin the past due to theireffectivenessin the selectiveoxidationof hydro-carbons",7,8.Propan-2-01undergoesboth dehydro-genationand dehydrationon theseoxides.The catalystsgroupedin Table 1 undergode-activationwith reactiontime until a low stableactivity is reached.The percentageof acetoneformedaftertheelapseof 5minfromthecommence-ment of the reactionis given in Table 1. Thecatalystsgroupedin Table2 do not showa decreasein activitywithtime. In thecaseof Co/vVmixtures,therewasconsiocrab]ecarbondepositionevenwhenoxygenwas presentin the feed. Antimonyoxideand tin oxidewereinactive.Theoxidesin Table1serveasa sourceof oxygenas well as 'catalysts'. The catalyticactivity de-clineswith usedueto oxygendepletion(reduction)in theoxide. Uponreoxidationof theagedcatalyst," ;·"11'11 I' Iii ISUBRAHMANYAM & KURIACOSE: BEHAVIOUR OF OXIDE CATALYSTS*Catalysts used show loss of activity with use. Bothdehydrogenationand dehydrationoccurredon the catalysts.tFor each catalyst the secondset of results is for theregeneratedcatalyst.TABLE 1- SALIENT FEATURESOF SOMEOXIDATIONCATALYSTSIN THE DECOMPOSITIONOF PROPAN-2-0L(Temp., 4000; contact time, 1 sec; wt of catalyst, 2 g)Catalyst* Acetone (%) per hr withduration (min) of runtin air the initial activity is completelyrestoredwhichcan beseen from the duplicatevalues inTable 1. The lossof oxygenduringreactionmaybe dueto the relativelyweaknatureof the metal-oxygen bonds. In the mixed oxide systemsingroup A, mutual interactionbetweenthe oxidesmay be weakeningthe metal-oxygenbond. Ithasbeenshownthattheenergyofbondingofoxygento a metallicoxide surfacegenerallyincreasesasoxygenis removed9and correspondinglythere isa decreasein dehydrogenationactivity to a lowvaluewithoutthe oxidebeingcompletelyreduced.Changesin thecatalyticpropertieswith composi-tion in complexoxidesystemsareoftenassociatedwith the formationof new compoundsand solidsolutions.For example,manyauthorsIOwhostudiedthe activity of tin-antimonyoxide catalystsforpartial oxidationof olefinshave shown that theactivecomponentin this systemis a solidsolutionof antimonyoxidein tin oxidewhile'in thesystemFe20a-MoOathe activecomponenthas beenshownto be normaliron molybdateII. It wasfoundthatin the oxidativeammonolysisof propyleneon bis-muth-molybdenumcatalysts,the mostactivecom-positioncorrespondsto the compoundBi_Oa-2MoOa([3-phase)12.The catalystsin Table 2, exhibitinga constantactivity for dehydrogenationof propan-2-ol,canbe consideredto be true dehydrogenationcatalystssincethey aid in the removalof hydrogenwithoutentering into a reaction with hydrogen.Theseoxidesarenotgoodcatalystsforthepartialoxidationof 01efins1a.ZrjMoBijWBijVVjMo5-1025-3040-45(a)1 811(b)2 15254(c)0 220(1: 1)418(7: 3)733 747(1: 1)263( : )9TABLE 2 - SALIENT FEATURESOF SOMEOXIDATIONCATALYSTSIN THE DECOMPOSITIONOF PROPAN-2-0L(Temp., 4000; contact time, 1 sec; wt of catalyst, 2 g)Catalyst*Acetone(%) perhr withType of reactionduration (min) of run5-1025-3040-45Zr0243Mostly d hydrationW031088 doTh029176Bothdeh droge a-tion and dehydra-tionCojMo(1: 1)40do(9: 1)97 3323 7381 92ZrjMo91do54Bi W9dot2 d tCoj3Vj65 dehydration(1:9)9dehydrogena-(1: 1)tion and dehydra-SbjW*The catalystsemployeddo not shewdecreasein dehydro-genationactivity with use.tVisualinspectionof agedcatalystshowedthat freebismuthoxide had got reducedto bismuth metal.tLots of carbondepositwasobservedevenin the presenceof oxygenin the feed.TABLE 3- HEATS OF FORMATIONOF OXIDESUCatalyst -!!.H29810-8Catalyst-!!. . OJ kg mole-1J kg mole-1Bi203577-778Th021227·5Sn0281·12Zr0 6 246b203699'614V.Os5 ' 83W03840 £ 7One may considerthat for selectiveoxidationthe energyof bondingof oxygento the catalystshouldnotbetoolowsincethenthetargetproductswill be further oxidized rapidly. For example,Bi20ais reducedto metalby propan-2-olat 4000givingriseto C92andH20(ref.13). On theotherhand,if the bondingis too strong,the oxygenwillnot be availablefor reactionat all. The heatsofformationof therelevantoxidesaregivenin Table3.587INDIAN J. CHEM., VOL. 15A, JULY 1977+TABLE 4 ~ CORRELATION BETWEEN OXYGEN MOBILITY ANDSELECTIVITy16The Jheatof formationof Th02 and Zr02 arenearlyiequaland they do not undergoreductionwhilepromotingthedehydrogenationof propan-2-ol,wherea$V205in spite of its higherheat of for-mation!undergoesreductionwhiledehydrogenatingpropan+2-01.Further, the heats of formationofSn02 ~nd Sb,,03are nearly equal and they arefound~obeinactivefor dehydrogenationof propan-2-01,"'*lereasBi203whichhas a heatof formationalmost[equalto that of theabovetvvooxidesunder-goes dompletereduction to metal and oxidizespropanr-2-olto carbondioxideandwater.If Hie heatsof formationof oxidescanbe takenas a nj1easureof the strengthof the metal-oxygenbond,theaboveobservationleadsto theconclusionthat t~estrengthof the metal-oxygenbondcannotbe th~only factor responsiblefor the selectivityof thd catalvst. However, Trifiro et al.l5 haveshown!a rei;ltionshipbetweenselectivity of anoxide~orthe oxidationof propyleneand mobilityf lat iceoxygen. The lattice oxygenwas d~terminedby isotopeexchangestudies.Molybdateswith very mobile lattice oxygenare nqt selectivein the oxidationof propylene,incontr$t to thosewith moderatelvmobile latticeoxygett(Table 4). Accordingto 'Trifiro et al. forselecti~eoxidationthe oxygenmobilitymusthavean optimumvalue.qatalystFe-Mo (~dustrial catalyst)Bi-:Mo IBi-Mo=1 (Erman phase)Mn-MoMoO.Co-MoMobilityHighLowHighLowHighSelectivityto acroleinLowHighLowHighLowThe dehydrogenationcatalystslisted in part Afunctionthrougha redox mechanismof the oxy-reductivetype17• Theoxygenreactswith hydrogenduringthedehydrogenation.As to themechanismof the reaction on the purely dehydrogenatingcatalysts, the first stage here too must be aninteractionof the moleculeto be reducedwith theoxygenof the catalysts,but the oxygenis notconsumed.This behaviourof the secondgroupcorrespondsto a simpledehydrogenationmechanism.Oxideswhichdehydrogenatepropan-2-olthroughan oxyreductivemechanismwithoutgettingreduc-ed to the metallicstateare also effectivecatalystsfor the selectiveoxidationof olefins while thosethat are purely dehydrogenatingdo not functionas oxidation catalysts.References1. BORESKOV, G. K, Adv. Catalysis,15 (1964), 285.2. TRIFIRO, 1<. & PASQUON, 1., J. Catalysis, 12 (1968),412.3. SAMPSON, R. J. & SHOOTER, D., Oxidation combustionreview,1 (1965), 223.4. VOGE, H. H. & ADAMS, C. R, Adv. Catalysis, relatedsubjects,17 (1967), 151.5. SKARCHENKO, V. E., Russianchem.Rev.,37 (1968), 1.6. KURIACOSE, J. c., DANIEL, C. & SWAMINATHAN, R,Indian ]. Chem.,7 (1969), 367.7. HABER, J., Intern. chem.Engng, 15 (1975), 21.8. GERMAIN, J. E., Intra-ScienceChem.Rept,Vol. 6,1972, 3.9. BORESKOV, G. H., Kinetika Kataliz, 8 (1967), 1020.10. GODIN, G., MAK-EEIN, K. E. & PORTER, E. A., ProceedingsoftheFourth InternationalCongressonCatalysis,Preprintof report No. 20, Moscow, 1968.11. BORESKOV, G. K., KOLOvERTNOV, L. M., KEFELI, L. M. &PLYASOVA, L. i\1., [{inetikaKataliz, 7 (1966), 144.12. KOLCHlN, 1. K., MARGOLIS, L. YA. & BOBKOV, S. S.,Neftekhimiya,4 (1964), 301.13. DANIEL, C., SUBRAHMANYAM, M. & KURIACOSE, J. C.,Indian J. Chem.,13 (1975), 419.14. SAMSONOV, G. Y, The oxidehandbook(IFI/Plenum).15. TRIFIRO, F., CENTOLA, P., PASQUON, 1. & JIRU, P.,Proceedingsof the Fourth International CongressonCatalysis,Paper 18, Moscow, 1968.16. TRIFORO, F. & PASQUON, 1., La ChemicaeL'Industria,53, N. 6, Giugno, 1971.17. KEULKS, G. W., ]. Catalysis,19 (1970),232., ~II IIilt

Behaviour of Oxide Catalysts During the Catalysed Reactions of Propan-2-ol

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Behaviour of Oxide Catalysts During the Catalysed Reactions of Propan-2-ol

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