The regioselective distribution of cobalt species in hollow MFI zeolite for efficient epoxidation of styrene

The metal species embedded in specific positions within the zeolite framework and their unique microenvironment exhibit fascinating effects on catalytic performance. Herein, we incorporated tetrahedrally coordinated Co 2+ into the framework of hollow silicate-1 zeolite and investigated the influence of halogen anions (Cl - , Br - and F - ) in the synthesized gel on the distribution of cobalt species in the channels. The addition of an appropriate amount of inorganic ammonium salts and seeds was found to be a necessary condition for cobalt incorporated into the framework. Notably, the Cl - anions present in the synthesis gel can induce more cobalt species located at the intersection cavity of silicate-1 (β-type). Comprehensive characterization results indicate that the tetrahedrally coordinated Co 2+ in the intersecting cavities of hollow zeolite appears to exhibit more efficient styrene epoxidation performance. This work presents a simple and cost-effective method to synthesize hollow cobalt-based zeolite with adjustable metal distribution in channels. By regulating the spatial distribution of cobalt species with halogens, the CS-0.1–0.5-Cl catalyst enhanced activity and selectivity in the epoxidation reaction of styrene to styrene oxide. Specifically, at a temperature of 80 °C after a reaction time of 6 h, the catalyst demonstrated a styrene oxide yield of 42.47 % and a excellent styrene oxide selectivity of 82.29 %.