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

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.