Chinese Journal of Catalysis ›› 2021, Vol. 42 ›› Issue (9): 1561-1575.DOI: 10.1016/S1872-2067(20)63759-7

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Structured binder-free MWW-type titanosilicate with Si-rich shell for selective and durable propylene epoxidation

Jinpeng Yin, Xin Jin, Hao Xu#(), Yejun Guan, Rusi Peng, Li Chen, Jingang Jiang, Peng Wu*()   

  1. Shanghai Key Laboratory of Green Chemistry and Chemical Processes, School of Chemistry and Molecular Engineering, East China Normal University, Shanghai 200062, China
  • Received:2020-12-11 Accepted:2021-01-11 Online:2021-09-18 Published:2021-05-16
  • Contact: Hao Xu,Peng Wu
  • About author:# E-mail: hxu@chem.ecnu.edu.cn;
    * Tel/Fax: +86-21-62232292; E-mail: pwu@chem.ecnu.edu.cn;
  • Supported by:
    National Natural Science Foundation of China(21533002);National Natural Science Foundation of China(21872052);National Natural Science Foundation of China(21972044);Ministry of Science and Technology of the People’s Republic of China(2016YFA0202804);Fundamental Research Funds for the Central Universities

Abstract:

Selective and durable fixed-bed catalysts are highly desirable for developing eco-efficient HPPO (hydrogen peroxide propylene oxide) process. The powder titanosilicate catalysts must be shaped before being applied in industrial processes. As the essential additives for preparing formed catalysts, binders are usually the catalytically inert components, but they would cover the surface and pore mouth of zeolite, thereby declining the accessibility of active sites. By recrystallizing the binder (silica)/Ti-MWW extrudates with the assistance of dual organic structure-directing agents, the silica binder was converted into MWW zeolite phase to form a structured binder-free Ti-MWW zeolite with Si-rich shell, which enhanced the diffusion efficiency and maintained the mechanical strength. Meanwhile, due to the partial dissolution of Si in the Ti-MWW matrix, abundant silanol nests formed and part of framework TiO4 species were transferred into open TiO6 ones, improving the accumulation and activation ability of H2O2 inside the monolith. Successive piperidine treatment and fluoridation of the binder-free Ti-MWW further enhanced the H2O2 activation and oxygen transfer ability of the active Ti sites, and stabilized the Ti-OOH intermediate through hydrogen bond formed between the end H in Ti-OOH and the adjacent Si-F species, thus achieving a more efficient epoxidation process. Additionally, the side reaction of PO hydrolysis was inhibited because the modification effectively quenched numerous Si-OH groups. The lifetime of the modified binder-free Ti-MWW catalyst was 2400 h with the H2O2 conversion and PO selectivity both above 99.5%.

Key words: Propylene epoxidation, Titanosilicate, Binder-free formed catalyst, Recrystallization, Microenvironment