Effect of hydrogen pre-treatment on the catalytic properties of Zn/HZSM-5 zeolite for ethylene aromatization reaction

Abstract

After hydrogen pre-treatment at different temperatures, the textural and physicochemical properties of Zn/HZSM-5 were studied by X-ray diffraction (XRD), N2 adsorption-desorption, Fourier transform infrared (FT-IR) spectroscopy, temperature programmed desorption of NH3 (NH3-TPD), and X-ray photoelectron spectroscopy (XPS) techniques. The results showed that the temperatures for hydrogen pretreatment of Zn/HZSM-5 exerted a significant influence on both the contents and state of zinc species. The pre-treatment with hydrogen at temperature higher than 600 °C resulted in a significant leaching of zinc species from the catalysts, which occurred due to the reduction and sublimation of zinc species. The XPS characterization revealed that the hydrogen pre-treatment at different temperatures causes the redistribution of ZnOH+ and ZnO species in the zeolite. A linear correlation between the amount of ZnOH+ species and the selectivity to aromatics over the Zn/HZSM-5 catalysts pretreated with hydrogen at different temperatures was observed, suggesting that ZnOH+ species may promote the formation of aromatics in ethylene aromatization reaction.