Improvement of catalyst stability during methane dehydroaromatization (MDA) on Mo/HZSM-5 comprising intracrystalline mesopores

Abstract

A new Mo/HZSM-5 catalyst (3 wt% Mo, Si/Al = 26) comprising a carbon-templated zeolite having intracrystalline mesopores sizing ca. 10–20 nm (HZSM-5-BP) has been prepared. For comparison purposes, an equivalent catalyst has also been prepared from a commercial zeolite (HZSM-5-ref). The materials have been extensively characterized by XRD, ICP-OES, N 2 physisorption, SEM-TEM, 27Al MAS NMR, FTIR-pyridine, NH 3-TPD, H 2-TPR, TG-DTG analyses and TPO, and their catalytic activity evaluated for methane dehydroaromatization (MDA) at 700 °C, 1 bar, and 1500 ml/g cat h. The hierarchical Mo/HZSM-5-BP catalyst displayed a lower deactivation rate during MDA than the reference one, leading to a higher and stable aromatics yield at T.O.S. above 3 h, despite a higher amount of less reactive coke (associated to the zeolite acid sites) was produced in the former. We hypothesize that the enhanced tolerance to carbon deposits of the carbon-templated zeolite could be related to the intracrystalline mesopores acting as a trap for coke molecules and leaving a higher fraction of acid sites within the channels active for aromatization.