The Study Of Catalysts For Non-oxidative Aromatization Of Methane And Propane

Conversion of Methane to aromatics by its low-temperature activation in the presence of higher hydrocarbon is of great scientific and practical importance.It also provides a new way of utilization of methane and natural gas.In this paper,the activation and aromatization of methane using propane as the co-reactant over metal-loaded HZSM-5 catalysts were studied.The activity,surface acidity,surface area and the carbon deposition of the catalysts were investigated by NH3-TPD,SEM, XRD,BET,TG-DTA,Near-IR Raman and UV-Raman spectrum.The results were as follows:Methane aromatization using propane as the co-reactant was obtained over Zn-La/HZSM-5.The methane activity reached the highest when 6%Zn and 1%La were loaded on the HZSM-5.The conversion of Methane and propane were 31.4% and 99.7%,respectively.The selectivity of aromatics was as high as 64.1%at 550℃and GHSV(CH₄+C₃H₈+N₂)600cm³g^-1h^-1with CH₄/C₃H₈ moral ratio 5.0.Further studies were carried out on catalyst refreshment by different conditions such as steam-refresh and air-refresh methods.The Influence of preparation method on the activity of the catalysts was investigated.It was found that the activity and stability of the step-impregnated catalyst were higher than that of the ion exchange-impregnation mixed-method prepared catalyst.The influence of catalysts prepared by zeolites with different sources and Si/Al ratio were investigated,and it showed great effects on aromatization.The aromatization processes on Pt/HZSM-5 and Ag/HZSM-5 catalysts were also studied.It had been conclusively conformed that the stability on fresh and refreshed Pt/HZSM-5 were both great.The effect of time on stream,space velocity,reaction temperature and feed gas composition(CH₄/C₃H₈)over Ga/HZSM-5 were investigated.It was found that methane conversion was promoted efficiently by co-added propane.This method could provide a new process for methane activation at low temperature. Further studies on CH₄-C₃H₈ aromatization and refreshment were carried out on Ga/HZSM-5 catalyst modified by a second metal element such as Cu,Pt and Pd.The experiments indicated that methane and propane co-activation was improved by adding Cu,Pt and Pd.The methane conversion was up to 26.0%and the stability of catalyst was enhanced.NH₃-TPD,DTA-TG,Near-IR Raman,UV-Raman and SEM were used to characterize the surface properties of the catalysts and carbon species.NH₃-TPD experiments indicated that the intensity and amount of strong acid decreased,and the amount of weak acid increased after the addition of Cu,Pt and Pd to Ga/HZSM-5.The changes of acidic sites might be the reason for M-Ga/HZSM-5 catalyst showing higher aromatization activity.In conclusion,the results show that methane can be activated using propane as co-reactant,and hence converted to higher hydrocarbons and aromatics with high conversion at low temperatures(≤550℃)。...