The Effect Of Catalyst Supports On Methane Non-oxidative Aromatization

Methane aromatization under non-oxidative condition is one of the important reactions in the field of direct conversion of methane to aromatics. It is of significance for the utilization of natural gas and the understanding of the nature of C-H bond activation in methane molecule. Recently, there is a great improvement in the investigation on the catalyst preparation and modification of methane non-oxidative aromatization. The research results show that. Mo/HZSM-5 has the good catalytic performance in methane non-oxidative aromatization. In order to actualize the reaction in the fixed bed reactor. it is significant to study the effect of molding method on the performance of the catalyst.The effect of SiO₂/Al₂O₃ ratio and crystal size of HZSM-5 zeolite on methane non-oxidative aromatization was studied in this paper. It is found that the conversion of methane and the yield of aromatics increased with the increase of the ratio of SiO₂/Al₂O₃. When the ratio of SiO₂/Al₂O₃ is 45, the catalyst exhibits the optimal catalytic performance. The naro-HZSM-5 exhibits the optimal performance than micro-HZSM-5 in some ways, so the better reaction activity is found on the catalyst with the small crystal granularity.The extruded Mo/nano-HZSM-5 catalysts with Al₂O₃ and SiO₂ as supports were tested in non-oxidative aromatization of methane. The Mo/nano-HZSM-5 catalysts were characterized by pyridine FT-IR and NH3-TPD methods. The pyridine FT-IR spectra indicate that with the increase of Al₂O₃ the ratio of Br(o|¨)nsted acid sites to Lewis acid sites on the catalyst sample decreases, thus the methane conversion decreases and the coke formation increases. The amount of Br(o|¨)nsted acid increases with increasing the amount of SiO₂ which resultes in an increase in methane conversion and a decrease in coke deposition.The extruded Mo/nano-HZSM-5 catalyst with Al₂O₃ and La₂O₃ as supports was also studied in non-oxidative aromatization of methane. The catalysts with Al₂O₃/La₂O₃ = 1 exhiobits the optimal performance, the methane conversion is 7.70%, and the yield of aromatization is 3.09%. The effect of the content of Mo on methane non-oxidative aromatization was also studied. The result shows that the catalyst which is modified by 6% Mo exhibits the optimal performance.