杂原子掺杂beta分子筛的烯烃环氧化催化性能  

Synthesis of heteroatom-substituted beta zeolites for catalytic epoxidation of cyclic olefins

作　　者：吴玉帅 尤晴 董旭杰 朱子麒 王旭 陈汇勇[1] 马晓迅[1] WU Yushuai;YOU Qing;DONG Xujie;ZHU Ziqi;WANG Xu;CHEN Huiyong;MA Xiaoxun(School of Chemical Engineering,Northwestern University,Xi’an 710069,Shaanxi,China)

机构地区：[1]西北大学化工学院,陕西西安710069

出　　处：《化工进展》2022年第8期4192-4203,共12页Chemical Industry and Engineering Progress

基　　金：国家自然科学基金(21978238);陕西省教育厅科学研究计划重点项目(21JY041)。

摘　　要：采用液-固相同晶取代法分别制备了W、Mo、V和Ti掺杂的四种杂原子beta分子筛,并以环己烯和环辛烯为探针底物分子,系统性评价了W-beta、Mo-beta、V-beta和Ti-beta催化烯烃环氧化反应性能。结果表明,所制备的四种杂原子beta分子筛均具有较高的结晶度,且完好继承了母体Al-beta分子筛的微孔结构与纳米颗粒形貌;由于离子半径和M—O键长的差异,W和Mo的骨架掺入量相对较低,V和Ti的掺入量相对较高;催化烯烃环氧化反应中,有限的活性金属含量导致W-beta和Mo-beta催化环烯烃的转化率低于V-beta和Ti-beta,但W-beta、Mo-beta、V-beta的反应转换频率(TOF)较高,说明W、Mo、V金属位点的活性更高;催化环己烯环氧化反应中,V-beta催化剂易引发烯丙基氧化副反应,环氧化物选择性低于其他三种催化剂,且V活性组分氧化物形态含量较高,反应过程中易脱落,导致V-beta催化剂循环再生性能较差;Ti掺杂beta催化剂表现出最佳的烯烃环氧化反应性能,提高Ti含量可有效提高反应转化率,但骨架Ti掺入量存在极值,过多的Ti物种趋向于氧化物形态,降低反应活性(TOF值),因此适宜的骨架Ti掺杂有利于Ti-beta分子筛催化烯烃环氧化反应。Four types of heteroatom-substituted beta zeolites were prepared by a post-synthetic method.Nanosized Al-beta was used as the dealumination substrate,followed by the incorporation of 4—6 transition-metal atoms(W,Mo,V,and Ti)into the framework of dealuminated beta.The obtained heteroatom-substituted beta zeolites(W-beta,Mo-beta,V-beta,and Ti-beta)well inherited the high crystallinity,large micropore volume and nanoparticle morphology from their parent Al-beta.However,the incorporation amounts of various heteroatoms were different due to the discrepancy in ion radiuses and M—O bond lengths,and V-beta,and Ti-beta showed much higher metal contents than W-beta and Mo-beta.The beta zeolites were further used as catalysts for the epoxidation of cyclohexene and cyclooctene.W-beta and Mo-beta revealed lower conversions of cyclic olefins but higher turnover frequency(TOF)values than V-beta and Ti-beta,indicating the higher activities of the W and Mo active sites.V-beta exhibited the highest conversion of cyclohexene due to its high content of V,but the epoxide selectivity over V-beta was much lower than that over the other heteroatom-substituted beta catalysts,which could be ascribed to the excess oxide species that promoted the side reaction of allylic oxidation.Besides,serious leaching of V species were observed for the V-beta catalyst that led to a poor recyclability in liquid-phase epoxidation reaction.Among all the heteroatom-substituted beta catalysts,Ti-beta exhibited the highest conversion and epoxide selectivity in the catalytic epoxidation of cyclic olefins.Moreover,the Ti active species in Ti-beta were quite stable,which further gave a superior recyclability of Ti-beta.In addition,the conversion of cyclic olefins over Ti-beta can be enhanced by increasing the content of Ti,but the excess Ti species tend to form the low-activity oxides and reduce the TOF value.

关 键 词：杂原子分子筛 beta分子筛 同晶取代 烯烃环氧化 环氧化合物 

分 类 号：O643.36[理学—物理化学]