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1、應(yīng)用理論計(jì)算研究MCM-22分子篩相鄰酸性位上乙烯和苯的吸附第29卷第4期Vol29No.4催化ChineseJournalofCatalysis2008年4月April2008文章編號(hào):0253—9837(2008)04036607應(yīng)用理論計(jì)算研究MCM.22分子篩相鄰酸性位上乙烯和苯的吸附倪丹,周丹紅,張佳(遼寧師范大學(xué)化學(xué)化工學(xué)院功能材料化學(xué)研究所,遼寧大連116029)研究論文:366～372摘要:應(yīng)用ONIOM計(jì)算方法研究了MCM一22分子篩超籠12元環(huán)上存在兩個(gè)酸性位時(shí)的酸強(qiáng)度及其與骨架鋁之間距離的關(guān)系,并研究_r乙烯和苯分子吸附的規(guī)律.計(jì)算采用52T簇
2、模型和B3LYP/6—31G/MND0方法.結(jié)果表明,存在兩個(gè)酸性位且兩個(gè)骨架鋁之間間隔1個(gè)骨架硅時(shí),酸強(qiáng)度比孤立的酸性位明顯降低;當(dāng)間隔的硅原子數(shù)增加時(shí),酸強(qiáng)度呈上升趨勢(shì),間隔3個(gè)以上骨架硅時(shí),其酸強(qiáng)度與孤立的酸性位幾乎沒(méi)有差別.對(duì)于乙烯的吸附,當(dāng)兩個(gè)骨架鋁之間問(wèn)隔1～4個(gè)骨架硅時(shí),其吸附能幾乎沒(méi)有差別(31～35kJ/mo1);對(duì)于苯的吸附,當(dāng)兩個(gè)骨架鋁之間間隔1個(gè)骨架硅時(shí),其吸附能有所提高,因?yàn)閮蓚€(gè)橋羥基同時(shí)對(duì)苯分子產(chǎn)生氫鍵吸附作用當(dāng)兩個(gè)骨架鋁之間的距離增大時(shí),苯的吸附能幾乎相同(21～29kJ/mo1)若兩個(gè)乙烯分子或苯分子同時(shí)吸附在雙酸性位上,其吸附能與單
3、個(gè)分子在孤立酸性位吸附時(shí)幾乎沒(méi)有差別.應(yīng)用自然鍵軌道計(jì)算分析了吸附配合物的電子結(jié)構(gòu),進(jìn)一步探明了乙烯和苯在分子篩酸性位上吸附的本質(zhì).關(guān)鍵詞:密度泛函;MCM22分子篩;乙烯;苯;吸附能中圖分類號(hào):0643文獻(xiàn)標(biāo)識(shí)碼:AStudyofEthyleneandBenzeneAdsorptiononBr6nstedAcidSitesinMCM.22ZeolitesbyTheoreticalCalculationNIDan,ZHOUDanhong,ZHANGJia(InstituteofChemistryJorFunctionalizedMaterials,Collegeof
4、ChemistryandCkemicalEngineeringLiaoningNormalUniversity,Dalian16029,Liaoning,China)Abstract:TheONIOMmethodwasusedtoperformthecomputationalstudyontheacidstrengthofdoubleacidsitesinthe12member—ringofMCM一22zeolite.ThecalculationwascarriedoutbytheB3IYP/6—31G"/MN—DOmethodbasedonthe52Tcluste
5、rmode1.rFhedependencyoftheacidstrengthontheintervaldistanceoftheframeworkAlatomswasexamined.andtheadsorptionofethyleneandbenzeneontheadjacentacidsiteswasin—vestigated.ThecalculationresultsindicatedthatwhentwoacidsitesexistedneareachotherandspacedoutbyoneSiatom,theaciditydescendsobvious
6、lywithrespecttotheisolatedacidsite.IftheSiatomnumberbetweentwoframeworkAlatomsincreases.theacidityrisesup.WhentheSiatomnumberismorethanthree.theacidstrengthreachesasteadyvalue,beingequivalenttolheisolatedsystem.ForC2H4adsorption,itsadsorptionen—ergyinallcasesis31—35kJ/mo1.independenton
7、theintervaldistancebetweentheframeworkAlatoms.ForC6H6benzeneadsorption,itsadsorptionenergyonnextnearestneighbouracidsitesishigherthanthatonsingleacidsite,andwhentheSiatomnumberismorethanthree,itsadsorptionenergyis21—29kJ/mo1.Theadsorp—tionenergyofeithertwoH4moleculesortwoC6H6molecule
