Structure and acidity of Mo/ZSM-5 synthesized by solid state reaction for methane dehydrogenation and aromatization

The Mo/ZSM-5 catalysts were synthesized by solid-state reaction with the mixture of MoO3 and HZSM-5 under N-2 atmosphere at 500 degrees C, and characterized by XRD, MAS NMR, BET, NH3-TPD, FT-IR and powder XRD structural analysis. The results showed that the Mo species were well dispersed on the internal and external surface of the zeolite ZSM-5, while the framework of ZSM-5 was retained. One part of Mo species inside the channels of ZSM-5 can be described as [Mo5O12](6+) units in the Mo/ZSM-5 with 8 wt% MoO3 loading. The [Mo5O12](6+) units are situated at the cross-point of the zigzag channel and the straight channel. They interacted with the framework of ZSM-5, and decreased the Bronsted acid sites remarkably. There was about 0.47 [Mo5O12](6+) unit in every cell of the ZSM-5 on an average. The other part of Mo species is distributed on the external surface of the ZSM-5 crystals, and can be described as crystallites of molybdenum oxides. The distribution of Mo species on HZSM-5 increased the Lewis acid sites in the catalysts. The [Mo5OxCy]"(+) units inside the channels of ZSM-5 partially reduced by methane maintained the catalytic activity of the catalysts and were beneficial for the formation of benzene during methane dehydrogenation and aromatization at 700 degrees C. (c) 2005 Elsevier Inc. All rights reserved.