Zeolites NaX were synthesized with the crystallization temperatures of 25 degrees C and 95 degrees C and converted into cobalt-exchanged catalysts (Co2+-NaX) by an ion-exchange method. The results indicated that zeolites synthesized at 25 degrees C were composed of many closely packed nanocrystals with the average size of around 30 mm, while the samples obtained at 95 degrees 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 degrees C zeolite sample) exhibited higher catalytic performances in epoxidation of styrene as compared with that of Co2+-NaX (95 degrees C zeolite sample) catalysts, which may be attributed to their short diffusion path and enhanced physical transport of reactants and products. (C) 2015 Elsevier Ltd. All rights reserved.