Synthesis of Zeolite NaA at Low Temperatures: Characterization, Cobalt Exchange and Enhanced Catalytic Activity of Styrene Epoxidation

Resumo

Zeolites NaA were synthesized with the crystallization temperatures of 25, 40, 60, and 95°C, then converted into Co²⁺–NaA catalysts by an ion-exchange method. The samples were characterized and the results revealed that the higher the reaction temperature, the shorter the crystallization time and the bigger the particle size of zeolite NaA will be. Zeolite NaA kept its crystal structure before and after cobalt exchange. However, the introduction of cobalt ions into zeolite would result in a decrease in the intensity of all crystallographic reflexes. Furthermore, Co²⁺–NaA (25°C zeolite sample) was shown to exhibit better catalytic activity of styrene epoxidation as compared with that of Co²⁺–NaA (40, 60, and 95° zeolite sample) catalysts, which may be ascribed to its short diffusion path and enhanced physical transport of reactant and product.