Studiesonethyleneoligomerizationandacid-catalyzedetherificationovernickelphosphidecatalysts

Abstract

Nickelphosphidecatalystshavebeenstudiedinhydrotreatingreactionssincetheyshowgoodcatalyticperformanceowingtometallicandacidicproperties.Therefore,theyareworthbeingstudiedtoextendtheirapplicationsbasedonunderstandingcatalystcharacteristics.Inthisthesis,supportednickelphosphide(Ni2P)catalystsareappliedforethyleneoligomerizationandacid-catalyzedetherificationthathaveneverbeenexploredsofarinliterature. Ethyleneoligomerizationplaysanimportantroleinpetrochemicalindustryinsuchawaythattheproducedoligomersareusedforvariouscommoditychemicals.Thewell-knowncatalystishomogeneousNicomplexinShellHigherOlefinProcess(SHOP),whichconsistsofNicenterandP–Osurroundingligands.SimilartotheSHOP-typecatalyst,thepreparedNi2P/SiO2-Al2O3catalystcontainsbothNi–PandP–Obonds.Whentestedwithco-catalystLiAlH4inethyleneoligomerization,theNi2P/SiO2-Al2O3catalystshowedthebestperformance,comparedtosupportedNiandNiOcatalysts.Particularly,thepresenceofLiAlH4largelycontributedtotheformationofoligomers,whichwaspronouncedathighertemperatures.Moreover,acidsitesascribedtoSiO2-Al2O3supportwereresponsibleforisomerizationofterminalolefinsintointernalandbranchedolefins.Inaddition,theeffectofsupportmaterialssuchasSiO2andAl2O3wasexamined.ThesizeofNi2PparticlesweredependentonthesupportduetothedifferentinteractionsofNiandPwitheachsupport.Amongthetestedcatalysts,theNi2P/SiO2exhibitedthebestactivityowingtothesmallestNi2Pparticles.Thecatalyticactivitywasconsideredtobeaffectedbythethreekeyproperties:1)smallNi2Pparticles,2)ahighratioofBrønstedacidsitetoLewisacidsite,and3)theabilitytoformnickelhydride(Ni–H)species.Consequently,itissuggestedthatethyleneoligomerizationcanproceedoverthesupportedNi2PcatalystsalongwithLiAlH4co-catalyst. SincetheNi2P/SiO2wasrevealedtopossessLewisandBrønstedacidsiteseventhoughSiO2supportisinert,itwouldbeworthwhilebeingtestedinthereactionsdemandingtheacidity,etherificationinthisthesis.Thus,thetestedsubstratewasfuranylalcoholsderivedfrombiomassinthesolventofaliphaticalcohols.The5-(alkoxymethyl)furfural,whichisapotentialcandidateasfueladditive,wassuccessfullyproducedbytheetherificationof5-(hydroxymethyl)furfural(HMF)withvariousaliphaticalcoholsoverNi2P/SiO2.ThecatalyticabilityofNi2P/SiO2wasconfirmedagainintheetherificationofvariousfuranylalcoholswithethanol.WhenthecatalystswithdifferentratiosofPtoNi,theP–OHgroupslocatedonNi2PparticlesandSiO2supportwereobservedtobehaveasBrønstedacid.Finally,theNi2P/SiO2couldberecycledafterheattreatmentunderH2inspiteofactivitylossbycokedeposition. Inthisthesis,theactivitiesofsupportednickelphosphidecatalystswereidentifiedinethyleneoligomerizationandacid-catalyzedetherification.Therefore,itisbelievedthatthereportedresultsanddiscussioncangreatlycontributetounderstandingthecatalyticbehaviorofNi2Pcatalystsandexpandingtheirapplicationtonewareas.