Methane dehydroaromatization by Mo-supported MFI-type zeolite with core–shell structure

Abstract

The MFI-type core–shell HZSM-5-Silicalite-1s (HZ5@S1) with various core/shell ratios were synthesized by the epitaxial growth of Silicalite-1 on HZSM-5, and the corresponding Mo/HZ5@S1 catalysts prepared by incipient wetness impregnation were tested in methane dehydroaromatization (MDA). Characterizations by XRD, ICP, NH3-TPD, DTBPy-FTIR, H2-TPR, SEM and 27Al MAS NMR showed that Silicalite-1 layer covering on HZSM-5 core can eliminate the external acid sites, and thus prevent the formation of active Mo species associated with Brønsted acid sites on the external surface of catalysts. Mo/HZ5@S1 catalysts presented high shape selectivity to aromatics and stability in MDA reaction as well as the gradual decrease in the selectivity of non-aromatic products. However, the overgrowth of Silicalite-1 shell will lead to a severe inhibition of the Mo species migrating into zeolite pores and consequent anchoring on the Brønsted acid sites of HZSM-5 core. In this sense, the catalytic performance is dependent on the core/shell ratio.