Preparation of core-shell structural twin HZSM-5@Silicalite-1 catalysts and its performance for toluene alkylation with methanol

The technology of alkylation of toluene with methanol to p-xylene has attracted much attention due to the high selectivity of p-xylene and low energy consumption in product separation unit. Twin HZSM-5 molecular sieve has the characteristics of large coverage proportion of zigzag channels on the surface and less aluminum distribution on the outer surface. It shows high selectivity for p-xylene in the alkylation of toluene and methanol. In this paper, silicalite-1 (S-1) was grown epitaxially on the surface of twin HZSM-5 molecular sieve by hydrothermal crystallization, and twin HZSM-5@Silicalite-1 core-shell catalyst was obtained. Compared with twin HZSM-5, HZSM-5@40Silicalite-1 core-shell catalyst shows excellent catalytic performance in toluene methanol alkylation. Under the reaction conditions of 470 ℃, 0.1 MPa and hydrogen atmosphere, the conversion of toluene is 8.5% and the selectivity of p-xylene is 98.4%. Then, the effect of solid-liquid mass ratio of nuclear HZSM-5 and silicalite-1 shell precursors on the growth of silicalite-1 crystal was further studied, and the effect of silicalite-1 on the catalytic performance of twin HZSM-5 was investigated. The pore structure and acid properties of core-shell materials were studied in detail by SEM, XRD, XRF, liquid static adsorption, N₂ adsorption desorption, NH₃-TPD and Py-FTIR.