催化学报 ›› 2025, Vol. 71: 158-168.DOI: 10.1016/S1872-2067(24)60241-X

• 论文 • 上一篇    下一篇

CO2促进的分子筛限域单位点铬体系催化乙苯高效脱氢

党健a,b, 邓欣a, 李玮杰a,*(), 杨迪a, 武光军a, 李兰冬a,*()   

  1. a南开大学化学学院, 有机新物质创造前沿科学中心, 天津 300071
    b南开大学材料科学与工程学院, 天津 300350
  • 收稿日期:2024-11-13 接受日期:2024-12-26 出版日期:2025-04-18 发布日期:2025-04-13
  • 通讯作者: * 电子信箱: liweijie@nankai.edu.cn (李玮杰), lild@nankai.edu.cn (李兰冬).
  • 基金资助:
    国家自然科学基金(U22B6011);国家自然科学基金(22025203);中国博士后科学基金(2023M731797);中央高校优秀青年团队项目(南开大学)

CO2-promoted ethylbenzene dehydrogenation catalyzed by zeolite-encaged single chromium sites

Jian Danga,b, Xin Denga, Weijie Lia,*(), Di Yanga, Guangjun Wua, Landong Lia,*()   

  1. aFrontiers Science Center for New Organic Matter, College of Chemistry, Nankai University, Tianjin 300071, China
    bSchool of Materials Science and Engineering, Nankai University, Tianjin 300350, China
  • Received:2024-11-13 Accepted:2024-12-26 Online:2025-04-18 Published:2025-04-13
  • Contact: * E-mail: lild@nankai.edu.cn (L. Li),liweijie@nankai.edu.cn (W. Li).
  • Supported by:
    National Natural Science Fund of China(U22B6011);National Natural Science Fund of China(22025203);China Postdoctoral Science Fund(2023M731797);Fundamental Research Funds for the Central Universities(Nankai University)

摘要:

通过活化烃类化合物的碳-氢键, 能够将价廉易得的烃类原料转化为高附加值化学品. 乙苯脱氢制备苯乙烯是聚苯乙烯及其衍生物生产的关键过程. 乙苯直接脱氢制苯乙烯工艺面临高能耗和催化剂不可逆失活等难题. 相比于直接脱氢, 氧化脱氢工艺具有能耗低和能够突破热力学限制等显著优势. 尤其是以CO2作为弱氧化剂时, 与氧气氧化剂相比, 不仅能降低过度氧化的风险, 而且可以实现CO2的资源化利用. 因此, 构建稳定且高效的CO2促进乙苯脱氢催化体系具有重要意义和挑战性.
本文采用原位配体保护的水热合成法, 将铬配合物(铬-3-氨丙基三乙氧基硅烷)封装在Y型分子筛中, 并经焙烧去除配体后, 成功合成Cr@Y分子筛催化剂. 该催化剂含有限域的孤立O=Cr(VI)=O物种, 并且通过分子筛骨架外的钾离子进行调控, 从而在CO2促进乙苯脱氢反应中展现出卓越性能. K-Cr@Y催化剂的初始乙苯转化率高达66%, 苯乙烯选择性达到96%, 优于其他类型的M-Cr@Y催化剂(M = Li, Na, Rb, Cs). 分子筛骨架外的钾离子能够调节限域Cr(VI)物种的电子密度, 从而促进乙苯分子中碳-氢键的活化. 表征分析结果表明, 在乙苯脱氢过程中, 限域的O=Cr(VI)=O物种会逐渐被还原为低活性的Cr(IV)=O物种, 而Cr(IV)=O可以通过简单的焙烧再生恢复为O=Cr(VI)=O物种. 原位红外光谱结果进一步阐明了CO2在乙苯脱氢反应中的关键促进作用, 即抑制限域Cr物种的过度还原, 防止其转化为非活性的Cr(III)物种, 并抑制焦炭沉积的发生.
综上所述, 本文为设计非贵金属催化剂用以实现CO2促进乙苯脱氢提供了新的思路, 尤其是对于通过分子筛骨架外阳离子调控限域高价过渡金属离子具有重要启示.

关键词: 碳-氢键活化, CO2促进乙苯脱氢, K-Cr@Y, O=Cr(VI)=O, Cr(IV)=O

Abstract:

The selective activation of C-H bonds is pivotal in catalysis for converting hydrocarbons into value-added chemicals. Ethylbenzene dehydrogenation to styrene is crucial process to produce polystyrene and its derivatives used in synthetic materials. Herein, K-Cr@Y with zeolite-encaged isolated O=Cr(VI)=O species modified by extraframework potassium ions is constructed, showing remarkable performance in CO2-promoted ethylbenzene dehydrogenation with initial ethylbenzene conversion of 66% and styrene selectivity of 96%, outperforming other M-Cr@Y catalysts (M = Li, Na, Rb, Cs). Extraframework potassium ions can modulate the electron density of zeolite-encaged Cr(VI) species and therefore facilitate C-H bond activation in ethylbenzene molecules. The gradual reduction of zeolite-encaged O=Cr(VI)=O to less active Cr(IV)=O species by dihydrogen during ethylbenzene dehydrogenation is evidenced by comprehensive characterization results, and Cr(IV)=O can be re-oxidized to O=Cr(VI)=O species upon simple calcination regeneration. The results from in situ DRIFT spectroscopy elucidate the critical promotion role of CO2 in ethylbenzene dehydrogenation over K-Cr@Y by retarding the over-reduction of zeolite-encaged Cr species to inactive Cr(III) species and suppressing coke deposition. This study advances the rational design of non-noble metal catalysts for CO2-promoted ethylbenzene dehydrogenation with zeolite-encaged high valence transition metal ions modulated by extraframework cations.

Key words: C-H bond activation, CO2-promoted ethylbenzene dehydrogenation, K-Cr@Y, O=Cr(VI)=O, Cr(IV)=O