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

Anew Mo/HZSM-5catalyst (3 wt% Mo, Si/Al = 26) comprising a carbon-templated zeolite having intracrystalline mesopores sizing ca. 10-20nm (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, (27)Al 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 degrees 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. (C) 2010 Elsevier B.V. All rights reserved.