Towards The Catalytic Performance For Methane Dehydro-aromatization Over Mo-based Catalysts

Methane dehydro-aromatization is one of the most effective routes for the activation and direct conversion of methane. After intensive efforts from some catalytic research groups worldwide for about 10 years, many encouraging progress in terms of methane activation and aromatization mechanism have been achieved. Up to now, it is generally accepted that Mo/HZSM-5 catalyst is a bifunctional catalyst, and Mo species in the form of either M02C or MoO_xCy are responsible for methane activation, while the Bronsted acid sites located in the channel of HZSM-5 are responsible for the formation of benzene. However, no much improvement has been made in catalytic performance for methane dehydro-aromatization over the Mo-based catalysts, especially in the catalytic stability. It is a vital drawback for potential industrial application that the activities of the catalysts in the methane conversion decline abruptly in a few hours due to the serious coke formation. Considering the problems, the emphases of this research have been placed on exploiting novel catalysts which possess the strong capacity of accommodating carbonaceous deposits and effective reduction of coke formation. As a result, improve their catalyst stability.Various techniques, such as specific surface area (BET), X-ray diffraction (XRD), temperature-programmed hydrogenation and Oxidation reaction (TPH/TPO), X-ray photoelectron spectroscopy(XPS), Fourier transformed infrared spectroscopy (FT-IR), ¹H, ²⁷Al, ²⁹Si nuclear magnetic resonance (NMR), temperature-programmed adsorption of NH3 (NH3-TPD), pyridine adsorption, etc., have been used to characterize the tested samples. On the basis of the characterization results, the effect of the pretreatment of parent-zeolite, the conditions and preparation methods of Mo/HZSM-5 catalysts on catalytic performance for methane dehydro-aromatization has been investigated. Meanwhile, the distribution and location of Mo species on the catalysts as well as interaction between Mo species and HZSM-5 and the type of carbonaceous deposits on the reacted catalysts, as well as the regeneration condition and methods of the deactivation catalysts have been studied in this dissertation of Ph. D.The effect of various ratio of Si/Al in HZSM-5 on the catalytic performance of Mo/HZSM-5 for dehydro-aromatization has been investigated. The result reveals that there...