Characteristic and mechanism of methane dehydroaromatization over Zn-based/HZSM-5 catalysts under conditions of atmospheric pressure and supersonic jet expansion

Abstract

The catalytic performance of Zn-based/HZSM-5 catalysts prepared by wet impregnation method was investigated for the methane dehydroaromatization (MDA) reaction under the conditions of atmospheric pressure and supersonic jet expansion (SJE). The physical properties of the catalysts were characterized by Brunauer-Emmett-Teller (BET), Fourier transform infrared (FT-IR), temperature-programmed reduction of H 2 (H 2-TPR), temperature-programmed desorption of NH 3 (NH 3-TPD), X-ray photoelectron spectroscopy (XPS), thermogravimetric and differential thermogravimetric (TG/DTG), and high-resolution transmission electron microscopy (HRTEM) techniques. The results revealed that under SJE condition the Zn/HZSM-5 catalyst exhibited high catalytic activity. It was found that because of the rapid migration of H + ions on the catalyst, the activation of CH 4 at active sites of nano-ZnO is facile. A new reaction mechanism that involves an active "ZnO-CH 3 +... -HZnO" intermediate formed as a result of synergetic action between ZnO and HZSM-5 has been proposed for CH 4 dissociation and dehydrogenation. Under atmospheric pressure, however, the catalytic activity of Zn/HZSM-5 is low. © 2011 American Chemical Society.