Steamed Zn/ZSM-5 catalysts for improved methanol aromatization with high stability

The effects of steam treatment on Zn species modified ZSM-5 (Zn/ZSM-5) were systematically studied by X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, Al-27 MAS NMR spectroscopy, inductively coupled plasma-optical emission spectroscopy, N-2 physisorption, NH3 temperature-programmed desorption, infrared spectroscopy of adsorbed pyridine, Raman spectroscopy and thermogravimetric analysis. It was found that Zn species could efficiently enhance the hydrothermal stability of ZSM-5. Moreover, the ZnO species was enriched on the surface of ZSM-5 after steam treatment, while ZnOH+ species almost kept constant. The catalytic performance of steamed and non-steamed catalysts was evaluated in the process of methanol to aromatics (MTA). Zn/ZSM-5 steamed at 400 degrees C exhibited higher selectivity for aromatics than non-steamed Zn/ZSM-5. The enhanced selectivity for aromatics was ascribed to the high retention ratio of Bronsted acid sites and newly created mesopores of Zn/ZSM-5 steamed at 400 degrees C. In addition, the steamed catalysts showed lower deactivation rate and more coke on external surface compared to non-steamed catalysts, which could be the reason for superior catalyst stability. (C) 2017 Elsevier B.V. All rights reserved.