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

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, H-2-TPR, SEM and Al-27 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 Bronsted 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 Bronsted acid sites of HZSM-5 core. In this sense, the catalytic performance is dependent on the core/shell ratio. (C) 2013 Elsevier B.V. All rights reserved.