Synthesis of zeolite NaX at 25 °C and 95 °C: Characterization, cobalt exchange and catalytic performance in epoxidation of styrene

• NaX were synthesized with the crystallization temperatures of 25 °C and 95 °C.
• Introduction of cobalt led to a decrease in intensity of crystallographic reflexes.
• NaX synthesized at 25 °C was composed of many closely packed nanocrystals.
• Co2+–NaX (25 °C zeolite sample) had better activities in epoxidation of styrene.

Zeolites NaX were synthesized with the crystallization temperatures of 25 °C and 95 °C and converted into cobalt-exchanged catalysts (Co2+–NaX) by an ion-exchange method. The results indicated that zeolites synthesized at 25 °C were composed of many closely packed nanocrystals with the average size of around 30 nm, while the samples obtained at 95 °C were big single crystals. Zeolite NaX before and after the cobalt exchange kept pure faujasite structure, however, the introduction of cobalt ions into zeolite would lead to a decrease in the intensity of all crystallographic reflexes. Moreover, Co2+–NaX (25 °C zeolite sample) exhibited higher catalytic performances in epoxidation of styrene as compared with that of Co2+–NaX (95 °C zeolite sample) catalysts, which may be attributed to their short diffusion path and enhanced physical transport of reactants and products.

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