co-mocmc和ni-mocmc催化剂的制备及加氢脱硫性能研究

co-mocmc和ni-mocmc催化剂的制备及加氢脱硫性能研究

al2o3通常用作研磨磨损催化剂的载体。在其自行研磨过程中，有两个过滤蚀头活性剂：i型活性中心因金属和载体之间的强烈相互作用而被完全分解，因此硫化作用效率较低。ii活性中心和载体的作用相对较弱，因此具有比i型中心更高的过滤活性。与al2o3相比，由于碳载体和莫哈布西翁的相互作用较弱，因此co-mos催化剂可以具有更高的有机分解效率。然而，以前的活性碳（ac）由于开口小，很容易被携带的金属堵塞，这不利于反应和产物的扩散，不利于分解金属氧化物。为了提高催化剂的活性，我们开发了一种制造cmc的方法。得到的样品比摩尔大一流（14002000ms）、孔径（3.7nm）和孔体积（1.44.2.72cm3）大。在这项工作中，我们使用了两种制备的介孔碳，并将其用于储存汽车和汽油的模型分解和脱火反应。Mo和W是常用的加氢脱硫活性金属,而Co和Ni是常用的助剂,且比Mo和W更容易硫化,生成热力学上稳定的脱硫活性低的硫化物.如果在浸渍时使用螯合剂,助剂Co或Ni的前驱体将优先与螯合剂作用生成螯合物,后者具有比Mo和W前驱体更高的硫化温度,因而有利于Co(Ni)-Mo-S型活性中心的形成[7~10].因此,本文以两种自制CMC为载体,在浸渍液中加入鏊合剂,采用等量浸渍法制备Co-Mo/CMC和Ni-Mo/CMC催化剂,其中Co-Mo/CMC用于模型汽油的加氢脱硫反应,并与工业催化剂Co-Mo/γ-Al2O3(DSO催化剂)进行比较,而Ni-Mo/CMC用于模型柴油的加氢处理,与工业催化剂FH-98进行比较.本文以两种不同的介孔碳CMC-1和CMC-2以及AC作为催化剂载体,载体的织构性质见表1.在催化剂制备过程中发现,螯合剂柠檬酸、乙二胺、乙二胺四乙酸(EDTA)和氨三乙酸(NTA)等的使用均提高了相应Co-Mo/CMC-1催化剂的活性,其中EDTA和NTA的促进作用更为显著,故本文以NTA为螯合剂.具体制备过程如下.将NTA溶解于25%氨水中,加入计量的Co(NO3)3·6H2O(NTA/Co=1.2,摩尔比),溶解后加入计量的(NH4)6Mo7O24·4H2O(Co/(Co+Mo)=0.25,摩尔比),得到的溶液用来浸渍干燥的CMC.浸渍后样品在373K干燥12h,即得Co-Mo/CMC催化剂,再在673K硫化3h后用于催化反应.其他催化剂通过相似方法制备,其中Ni前驱体为Ni(NO3)3·6H2O.反应和测试条件见文献[11~14].表1列出了载体和催化剂的织构性质.由表可见,本文使用的CMC具有比AC更大的孔体积和孔径.Co-Mo/CMC-1和Ni-Mo/CMC-2催化剂孔体积较大,分别为1.05和0.82ml/g;而AC担载的Co-Mo催化剂孔体积由于载体孔体积和孔径较小而几乎消失.图1为CMC-1和Co-Mo/CMC-1催化剂硫化前后的XRD谱.由图可见,Co-Mo/CMC-1催化剂在硫化前后只出现介孔碳的衍射峰,表明Co和Mo高度分散在载体上.图2比较了Co-Mo/CMC-1,Co-Mo/AC和工业催化剂Co-Mo/γ-Al2O3上噻吩加氢脱硫活性.可以看出,Co-Mo/CMC-1的活性比Co-Mo/AC及CoMo/γ-Al2O3高得多.493K时Co-Mo/CMC-1上噻吩转化率比553K时Co-Mo/γ-Al2O3上的还要高.可见,采用Co-Mo/CMC-1为催化剂时的反应温度可比Co-Mo/γ-Al2O3的低60K.在493K,Co-Mo/CMC-1上噻吩转化率超过95%,而在载体CMC-1上转化率不到5%(未示出).这表明在Co-Mo/CMC-1上,噻吩的连续转化是通过加氢脱硫而不是通过载体吸附脱硫的方式实现的.柴油中的有机硫化物主要是二苯并噻吩(DBT)和烷基取代的二苯并噻吩,这些有机硫化合物比噻吩具有更大的分子尺寸,更难被脱除.此外,柴油中的稠环芳烃也需加氢以提高柴油的十六烷值和减少燃烧时颗粒物的排放.因此,具有较大孔径的载体将有利于较大分子尺寸的有机硫化合物和稠环芳烃在催化剂孔道中的扩散.我们使用孔径更大的CMC-2来担载Ni-Mo催化剂,用于模型柴油的加氢脱硫反应,结果见图3.由图可见,Ni-Mo/CMC-2具有比工业催化剂FH-98高得多的DBT加氢脱硫活性,593K时,FH-98催化剂上DBT转化率为97.8%,而Ni-Mo/CMC-2催化剂上为100%.此外,Ni-Mo/CMC-2的低温活性明显高于FH-98,前者在553K时的脱硫活性比FH-98在593K时的活性还要高.这表明以Ni-Mo/CMC-2为催化剂时的反应温度可以比FH-98的低40K.综上所述,介孔碳可用来担载Co-Mo-S和Ni-Mo-S催化剂,分别用于模型汽油和模型柴油加氢脱硫反应,其活性远高于传统的工业催化剂.英译文EnglishTextInHDScatalysts,MoandWareactivemetalswhileCoandNiarepromoters.CoandNiundergosulfidationfastethantheactivemetalsandformstablesulfideswithlowHDSactivities.Whenachelatingagentisused,thesulfidationofpromotersisretardedandtheactivemetalsundergosulfidationfirstleadingtocatalystswithhigherHDSactivities[7–10].Inthiswork,Co-Mo/CMCandNi-Mo/CMCwerepreparedbyimpregnationwithachelatingagent.TheCo-Mo/CMCwastestedfortheHDSofamodelgasolinecontainingthiopheneandcomparedwithacommerciaCo-Mo/γ-Al2O3catalyst(DSOcatalyst).TheNi-MoCMCwasexaminedfortheHDSofamodeldieselcontainingdibenzothiophene(DBT)andcomparedwithacommercialFH-98catalyst.Table1showsthetexturalpropertiesofthesupportsandsupportedcatalysts.ThedatainTable1showsthattheporevolumesoftheCMCsupportsweremuchhigherthanthaofAC.Accordingly,theporevolumesremainhighfortheCMCsupportedcatalystswhilethatofACalmostdisappeared.Apparently,thetexturalpropertiesoftheCMCsweremuchbetterthanthoseofACforthesupportedHDScatalysts.Figure1showstheXRDpatternsofCMC-1andCo-MoCMC-1beforeandaftersulfidation.TheXRDpatternsonlyshowsignalsfromtheCo-Mo/CMC-1catalystsupportsbeforeandaftersulfidationindicatingahighdispersionofsupportedCo-MospeciesonCMC-1.Figure2comparesCo-Mo/CMC-1withCo-Mo/ACandcommercialCo-Mo/γ-Al2O3fortheHDSofthiopheneinamodelgasoline.Apparently,Co-Mo/CMC-1ismuchmoreactivethanCo-Mo/ACandCo-Mo/γ-Al2O3.Moreimportantly,theconversionofthiopheneonCo-Mo/CMC-1at493KwashigherthanthatonCo-Mo/γ-Al2O3at553KindicatingthatCo-Mo/CMC-1worksatatemperature60KlowerthanCo-Mo/γ-Al2O3.At493K,morethan95%thiophenewasconvertedonCo-Mo/CMC-1,whilethedecreaseinthiophenewaslessthan5%ontheCMC-1supportunderthesameconditions(notshown).Thereforethecontinuousremovalofthiophenebyitsadsorptiononthesupportonlyisunlikely.DieselfuelsmaycontainsulfurintheformofDBTor4,6-dimethyldibenzothiophene(4,6-DMDBT),andthesearemuchmoredifficulttoremovethanthiophene.Inadditiondieselfuelscontainpolycyclicaromatichydrocarbons(PAH)thatshouldbehydrogenatedtoincreasethecetanenumberandtodecreasetheemissionofparticularmaterials.Therefore,supportswithlargeporesaredesiredtohydrotreattheabove-mentionedorganicsulfursandlargemolecularweightPAHsindieselstreams(whichalsocontainhydrocarbonswithmolecularweightssignificantlyhigherthanthoseingasoline).Inthiswork,amesoporouscarbon(CMC-2,seeTable1)withalargeraverageporediameterwasusedtosupportNi-Mo.Inconclusion,CMCwereusedtosupportCo-Mo-SandNi-Mo-SforHDSreactions.Co-Mo-S/CMCandNi-Mo-S/CMCwerefoundtobehighlyactivefortheHDSofthiopheneandDBTinmodelgasolineanddieselfuels,respectively.Full-textpaperavailableonlineatScienceDirectAluminaisafrequentlyusedsupportforhydrodesulfurization(HDS)catalysts.IthasbeenestablishedthattwotypesofCo-Mo-SHDSactivesitesmightexistonalumina.TypeIconsistsoftheMospeciesthatstronglyinteractswithaluminaanditisnotcompletelyconvertedtothesulfidesandhenceisnotactive.Incontrast,typeIIistheCo-Mo-Sspeciesthatdoesnotstronglyinteractwithaluminaand,therefore,itistheactivespeciesinHDS.Bycomparisontoalumina,carbonsupportshaveweakerinteractionswithmolybdenumandsupportedCo-Mo-Scatalysts,andtherefore,havehigherHDSactivities.However,traditionalactivatedcarbons(AC)havesmallporesthatareeasilyblockedbythesupportedspecies.Incontrast,mesoporouscarbonshavelargerporesandhavebeenusedascatalystsupports.Recently,wedevelopedacost-effectivemethodforthepreparationofmesoporouscarbonsanddesignatedthemCMC.Thesecarbonmaterialspossesshighsurfaceareas(1400–2000m2/g),largeporevolumes(1.44–2.72cm3/g)and100%mesoporeswithaveragediametersof3–7nm.Inthiswork,twoCMCswereusedtosupportCo-Mo-SandNi-Mo-SforHDSreactions.TwodifferentCMCswereusedinthiswork.ThetexturalpropertiesofthesupportsareshowninTable1.DuringthepreparationoftheHDScatalysts,weuseddifferentchelatingagents,whichincludedcitricacid,ethylenediamine,ethylenediaminetetraaceticacid,andnitrilotriaceticacid(NTA).NTAwasfoundtobeagoodchelatingagentforthepreparationofCo-MoandNi-MosupportedonaCMC.ThecatalystCo-Mo/CMCwaspreparedbytheincipientwetnessimpregnationmethod.NTAwasdissolvedina25%ammoniasolution,followedbyadditionoftherequiredamountofcobaltnitrate(NTA/Comolarratio=1.2).Afterthecompletedissolutionofcobaltnitrate,therequiredamountofammoniumheptamolybdate(AHM)wasa