Synthesis optimization of mesoporous ZSM-5 through desilication-reassembly in the methanol-to-propylene reaction

Hierarchical H-ZSM-5 zeolites were synthesized using desilication and desilication-reassembly methods. The catalytic performance of the synthesized catalysts was studied in methanol-to-propylene in a fixed-bed reactor under atmospheric pressure, 480 A degrees C and WHSV of 0.9 h(-1). Response surface methodology based on the Box-Behnken design was employed to optimize the three important variables: NaOH/ZSM-5 molar ratio, CTAB/ZSM-5 molar ratio and time of reassembly for optimizing propylene selectivity. Physiochemical properties of the catalysts were studied by XRD, FE-SEM, BET, NH3-TPD, TGA and FT-IR tests. The significant increase in the external surface area, pore size distribution in the range of 2-6 nm and decrease in the Bronsted acidity for desilication-reassembly product were observed. The hierarchical pore system and modification of the acidity in addition to protecting the zeolite structure increased the useful lifetime of the catalyst, selectivity of propylene and P/E ratio.