Chemical Industry and Engineering Progress ›› 2022, Vol. 41 ›› Issue (8): 4192-4203.DOI: 10.16085/j.issn.1000-6613.2021-2097

• Industrial catalysis • Previous Articles     Next Articles

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

WU Yushuai(), YOU Qing, DONG Xujie, ZHU Ziqi, WANG Xu, CHEN Huiyong(), MA Xiaoxun   

  1. School of Chemical Engineering, Northwestern University, Xi’an 710069, Shaanxi, China
  • Received:2021-10-11 Revised:2022-01-14 Online:2022-08-22 Published:2022-08-25
  • Contact: CHEN Huiyong

杂原子掺杂beta分子筛的烯烃环氧化催化性能

吴玉帅(), 尤晴, 董旭杰, 朱子麒, 王旭, 陈汇勇(), 马晓迅   

  1. 西北大学化工学院,陕西 西安 710069
  • 通讯作者: 陈汇勇
  • 作者简介:吴玉帅(1998—),男,硕士研究生,研究方向为杂原子掺杂beta分子筛的烯烃环氧化催化性能。E-mail:wuyushuai@stumail.nwu.edu.cn
  • 基金资助:
    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)

Abstract:

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.

Key words: heteroatom-substituted zeolite, beta zeolite, isomorphous substitution, alkene epoxidations, epoxides

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。

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

CLC Number: 

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