Abstract
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, 27Al MAS NMR spectroscopy, inductively coupled plasma-optical emission spectroscopy, N2 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°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 Brønsted acid sites and newly created mesopores of Zn/ZSM-5 steamed at 400°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.
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