Dehydroaromatization of methane under non-oxidative conditions over bifunctional Mo/ITQ-2 catalysts

Bifunctional Mo/ITQ-2 catalysts have been used for the methane dehydroaromatization (MDA) reaction. The SUM ratio, and thus the Bronsted acidity, of the zeolite affected the conversion, the fort-nation rate of aromatics, and the selectivity to the different products (CO, C-2, benzene, toluene, and naphthalene). Maximum activity and aromatics productivity were obtained for the zeolite with the lowest Si/Al ratio (Si/ Al = 15) presenting the highest Bronsted acidity, while maximum benzene selectivity (similar to 70%) occurred for the zeolite with Si/Al = 25. The selectivity to naphthalene increased with decreasing the Si/Al ratio, that is, with increasing the density of surface Bronsted acid sites. At comparable Si/Al ratio, Mo/MCM-22 was more active and selective to benzene than Mo/ITQ-2. Reduction of surface acidity in ITQ-2 by treatment with oxalic acid significantly reduced the formation of naphthalene, resulting in enhanced benzene selectivity (similar to 75%). The acid-treated ITQ-2 was even more selective to benzene than the Mo/MCM-22 catalyst (similar to 65%). Molecular dynamics simulations were performed at the MDA reaction temperature (973 K) to study the diffusion of naphthalene in the two independent pore systems of MCM-22. The theoretical results allowed explaining the differences in selectivity between the two zeolite structures and the effect of surface dealumination in ITQ-2. (c) 2005 Elsevier B.V. All rights reserved.