Synthesis and catalytic activity of hierarchical NbS-1 zeolites for cyclohexene oxidation

Abstract By suppressing fast hydrolysis of niobium ethoxide, which is suggested to be the key step for the NbS-1 zeolite synthesis, a NbS-1 zeolite with the average size 400–500 nm, Si/Nb ratio 28 and much large specific surface area (434 m2/g) was successfully synthesized. By treating this NbS-1 respectively in desilication at 353 K and dissolution-recrystallization at 443 K in TPAOH solutions, hierarchical NbS-1 zeolite with significant amount of cylindrical mesopores connecting to the external surface or multi-hollow single-crystal NbS-1 zeolite with dense shell being composed of pure S-1 zeolite were obtained. Thanks to the special structure, the hierarchical NbS-1 displayed much higher activity for the cyclohexene oxidation in liquid phase at 60 °C, over which 28.6% cyclohexene conversion with 64.5% selectivity to cyclohexene oxide was observed within the reaction period of 4 h.