Hierarchical Titanium Silicalite-1 Zeolites Featuring an Ordered Macro–Meso–Microporosity for Efficient Epoxidations

Abstract

The epoxidation reaction over titanium silicalite-1 (TS-1) zeolites is a green way to produce epoxides that are important intermediates for chemicals. Nevertheless, the conventional microporous TS-1 zeolite shows limited diffusion ability for bulky molecules, leading to poor activity and low selectivity. Constructing hierarchical porosity in microporous materials is an effective strategy to enhance the diffusion properties of catalysts. However, there are few reports on the design and synthesis of TS-1 zeolites with hierarchical structure featuring multilevels, interconnectivity, and regularity for efficient diffusion and epoxidations. Herein, hierarchical TS-1 zeolites with ordered macro–meso–microporosity (OMMM-TS-1) are obtained by a method combining a templated effect of ordered macro–mesoporous matrices and a confined in situ crystallization process. The OMMM-TS-1 possesses ordered macropores with tunable size (∼200–600 nm), ordered mesopores (∼8 nm), and intact micropores (∼0.5 nm). The OMMM-TS-1 achieves a cyclooctene conversion as 3.6 times and 1.8 times and a selectivity to epoxy product as 1.6 times and 1.3 times higher than the conventional TS-1 (C-TS-1) and nanosized TS-1 (Nano-TS-1) zeolites, respectively. The OMMM-TS-1 also outperforms the C-TS-1 and Nano-TS-1 zeolites in epoxidations of a series of alkenes. Such a novel hierarchical structure can be applied in the design and synthesis of many other catalysts.

Review and perspectives on TS-1 catalyzed propylene epoxidation

“…Graded TS-1 is usually synthesized by hydrothermal modification. 79 Different templating agents are added or the synthesis parameters are changed during the synthesis process. 80 , 81 , 82 , 83 The synthesized graded TS-1 has different pore sizes thereby increasing the external surface area and diffusion capacity.…”

Zeolite Crystal Engineering

“…architectures. − Soft templating techniques have been used as bottom-up approaches, whereas postsynthesis modification offers a top-down approach to enhance diffusion properties of zeolitic materials. Methods that combine heteroatom (e.g., Ti) incorporation in the design of hierarchical materials is also discussed in this virtual special issue. , …”

“…Methods that combine heteroatom (e.g., Ti) incorporation in the design of hierarchical materials is also discussed in this virtual special issue. 25,26 ■ ELUCIDATING AND OPTIMIZING…”

Novel-ordered hierarchical ZSM-5 zeolite with interconnected macro–meso–microporosity for the enhanced methanol to aromatics reaction

“…7,8 Hierarchical zeolites are designed to possess additional mesopores or macropores, providing a pathway for efficient mass transport and minimizing diffusional limitations. 9,10 The incorporation of interconnected macro–meso–microporosity in ZSM-5 zeolites can enhance the accessibility of active sites and shorten the diffusion path length, thus reducing the diffusion constraints and improving the conversion of methanol to aromatics. 11 Considerable efforts have been devoted to developing new strategies including the hard/soft-template method and post-treatment to introduce additional mesopores or/and macropores into the microporous zeolite to enhance the mass transportation properties for catalytic performance.…”