A new stratagem to efficiently synthesize monolithic TS-1 via dry gel conversion in the atmosphere of tripropylamine-water and revealing insight into the structure–activity relationship for propylene epoxidation

The epoxidation of propylene catalyzed by TS-1 possesses the advantages of high atomic utilization and mild reaction conditions. To explore the structure–activity relationship of the catalyst, carbon nanotubes grown on the surface of nickel foam were used as the carrier to synthesize monolithic TS-1 by dry gel conversion in the tripropylamine-water gas environment. Compared with the powder TS-1 by hydrothermal crystallization, the crystallization time of monolithic TS-1 was shortened from 72 h to 12 h. Tripropylamine promoted the dissociation of dry gel by increasing the basicity of liquid film on the surface of dry gel. Water provided the necessary pressure for crystallization and was also the medium of mass transfer in the process of crystallization. Stepwise regression analysis showed the increase of Lewis acid content and pore volume improved the conversion and utilization of hydrogen peroxide and the selectivity of propylene to propylene oxide.