Optimization of conditions for preparation of ZSM-5@silicalite-1 core–shell catalysts via hydrothermal synthesis

Although the preparation of ZSM-5@silicalite-1 (ZS) core–shell catalysts has been reported in the literature, their selectivity to para-xylene (PX) in the toluene alkylation with methanol is difficult to control. Here we present the effects of water and ZSM-5 adding amounts in the synthesis solution, the hydrothermal synthesis time, and the Si/Al ratio of core ZSM-5 on the catalytic performance of ZS core–shell catalysts. The ZS core–shell catalysts were characterized by X-ray diffraction (XRD), N2 adsorption, and NH3 temperature-programmed desorption (NH3-TPD) techniques. The highest PX selectivity of 95.5% was obtained for the ZS (Si/Al = 140) catalyst prepared in the synthesis solution with a molar ratio of 0.2TPAOH:1TEOS:250H2O at 175 °C and 10 r·min−1 for only 2 h and the corresponding toluene conversion is as high as 22.8% for the alkylation of toluene with methanol.