Effects of different phosphorus modification methods on acid and catalytic properties of nano-sized ZSM-5 zeolite in toluene alkylation with methanol

Nano-sized ZSM-5 zeolite was prepared via a vapor-phase transport method and then loaded with similar phosphorus content through different ways of phosphorus modification. These zeolites were characterized by XRD, SEM, N-2 adsorption-desorption, NH3-TPD, FT-IR, etc., and the catalytic property of the zeolites in toluene alkylation with methanol was studied. The results showed that after phosphorus modification, the ratios of Bronsted to Lewis acid sites (B/L) and weak to strong acid sites (W/S) increased. It was found that higher B/L and W/S ratios of the catalysts were beneficial to improve the catalytic stability in toluene alkylation with methanol. The coke deposition rate of the phosphorus-modified ZSM-5 samples was lower than that of parent ZSM-5. There were great differences in the ratios of B/L and W/S of samples through different ways of phosphorus modification. The phosphorus-modified ZSM-5 using the incipient wetness impregnation method, having the highest ratios of B/L and W/S, exhibited the best catalytic stability and the highest toluene conversion in toluene alkylation with methanol.