co-mocmc和ni-mocmc催化劑的制備及加氫脫硫性能研究

co-mocmc和ni-mocmc催化劑的制備及加氫脫硫性能研究

al2o3通常用作研磨磨損催化劑的載體。在其自行研磨過程中，有兩個過濾蝕頭活性劑：i型活性中心因金屬和載體之間的強烈相互作用而被完全分解，因此硫化作用效率較低。ii活性中心和載體的作用相對較弱，因此具有比i型中心更高的過濾活性。與al2o3相比，由于碳載體和莫哈布西翁的相互作用較弱，因此co-mos催化劑可以具有更高的有機分解效率。然而，以前的活性碳（ac）由于開口小，很容易被攜帶的金屬堵塞，這不利于反應(yīng)和產(chǎn)物的擴散，不利于分解金屬氧化物。為了提高催化劑的活性，我們開發(fā)了一種制造cmc的方法。得到的樣品比摩爾大一流（14002000ms）、孔徑（3.7nm）和孔體積（1.44.2.72cm3）大。在這項工作中，我們使用了兩種制備的介孔碳，并將其用于儲存汽車和汽油的模型分解和脫火反應(yīng)。Mo和W是常用的加氫脫硫活性金屬,而Co和Ni是常用的助劑,且比Mo和W更容易硫化,生成熱力學(xué)上穩(wěn)定的脫硫活性低的硫化物.如果在浸漬時使用螯合劑,助劑Co或Ni的前驅(qū)體將優(yōu)先與螯合劑作用生成螯合物,后者具有比Mo和W前驅(qū)體更高的硫化溫度,因而有利于Co(Ni)-Mo-S型活性中心的形成[7~10].因此,本文以兩種自制CMC為載體,在浸漬液中加入鏊合劑,采用等量浸漬法制備Co-Mo/CMC和Ni-Mo/CMC催化劑,其中Co-Mo/CMC用于模型汽油的加氫脫硫反應(yīng),并與工業(yè)催化劑Co-Mo/γ-Al2O3(DSO催化劑)進行比較,而Ni-Mo/CMC用于模型柴油的加氫處理,與工業(yè)催化劑FH-98進行比較.本文以兩種不同的介孔碳CMC-1和CMC-2以及AC作為催化劑載體,載體的織構(gòu)性質(zhì)見表1.在催化劑制備過程中發(fā)現(xiàn),螯合劑檸檬酸、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應(yīng)Co-Mo/CMC-1催化劑的活性,其中EDTA和NTA的促進作用更為顯著,故本文以NTA為螯合劑.具體制備過程如下.將NTA溶解于25%氨水中,加入計量的Co(NO3)3·6H2O(NTA/Co=1.2,摩爾比),溶解后加入計量的(NH4)6Mo7O24·4H2O(Co/(Co+Mo)=0.25,摩爾比),得到的溶液用來浸漬干燥的CMC.浸漬后樣品在373K干燥12h,即得Co-Mo/CMC催化劑,再在673K硫化3h后用于催化反應(yīng).其他催化劑通過相似方法制備,其中Ni前驅(qū)體為Ni(NO3)3·6H2O.反應(yīng)和測試條件見文獻[11~14].表1列出了載體和催化劑的織構(gòu)性質(zhì).由表可見,本文使用的CMC具有比AC更大的孔體積和孔徑.Co-Mo/CMC-1和Ni-Mo/CMC-2催化劑孔體積較大,分別為1.05和0.82ml/g;而AC擔載的Co-Mo催化劑孔體積由于載體孔體積和孔徑較小而幾乎消失.圖1為CMC-1和Co-Mo/CMC-1催化劑硫化前后的XRD譜.由圖可見,Co-Mo/CMC-1催化劑在硫化前后只出現(xiàn)介孔碳的衍射峰,表明Co和Mo高度分散在載體上.圖2比較了Co-Mo/CMC-1,Co-Mo/AC和工業(yè)催化劑Co-Mo/γ-Al2O3上噻吩加氫脫硫活性.可以看出,Co-Mo/CMC-1的活性比Co-Mo/AC及CoMo/γ-Al2O3高得多.493K時Co-Mo/CMC-1上噻吩轉(zhuǎn)化率比553K時Co-Mo/γ-Al2O3上的還要高.可見,采用Co-Mo/CMC-1為催化劑時的反應(yīng)溫度可比Co-Mo/γ-Al2O3的低60K.在493K,Co-Mo/CMC-1上噻吩轉(zhuǎn)化率超過95%,而在載體CMC-1上轉(zhuǎn)化率不到5%(未示出).這表明在Co-Mo/CMC-1上,噻吩的連續(xù)轉(zhuǎn)化是通過加氫脫硫而不是通過載體吸附脫硫的方式實現(xiàn)的.柴油中的有機硫化物主要是二苯并噻吩(DBT)和烷基取代的二苯并噻吩,這些有機硫化合物比噻吩具有更大的分子尺寸,更難被脫除.此外,柴油中的稠環(huán)芳烴也需加氫以提高柴油的十六烷值和減少燃燒時顆粒物的排放.因此,具有較大孔徑的載體將有利于較大分子尺寸的有機硫化合物和稠環(huán)芳烴在催化劑孔道中的擴散.我們使用孔徑更大的CMC-2來擔載Ni-Mo催化劑,用于模型柴油的加氫脫硫反應(yīng),結(jié)果見圖3.由圖可見,Ni-Mo/CMC-2具有比工業(yè)催化劑FH-98高得多的DBT加氫脫硫活性,593K時,FH-98催化劑上DBT轉(zhuǎn)化率為97.8%,而Ni-Mo/CMC-2催化劑上為100%.此外,Ni-Mo/CMC-2的低溫活性明顯高于FH-98,前者在553K時的脫硫活性比FH-98在593K時的活性還要高.這表明以Ni-Mo/CMC-2為催化劑時的反應(yīng)溫度可以比FH-98的低40K.綜上所述,介孔碳可用來擔載Co-Mo-S和Ni-Mo-S催化劑,分別用于模型汽油和模型柴油加氫脫硫反應(yīng),其活性遠高于傳統(tǒng)的工業(yè)催化劑.英譯文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