The Study Of Catalysts Modified By Metals In Non-oxidative Aromatization Of Mixed Methane And Propane

Conversion of Methane to aromatics at low-temperature in the presence of higher hydrocarbon is of great scientific and practical importance. This method also provides a new way of utilization of methane and natural gas. In this paper, the activation and aromatization of methane using propane as co-reactant over metal-loaded HZSM-5 catalysts were studied. The activity, structure and the deposited carboneous species of the catalysts were investigated by using NH3-TPD, TG, UV-Raman and TPO/TPH.A series of catalysts were prepared by normal ion-exchange,the modified metals including Mg, Ca, Sr, Ba, La, Zn, Sm,Eu and Gd. The influence of different modified metals on activity was investigated. It shows that the Zn modified catalysts have better performance in aromatization.Methane aromatization using propane as co-reactant was obtained over Zn /HZSM-5. The conversion of methane and propane was 15% and 99%, respectively, and the selectivity of aromatics was as high as 80% at 823K and GHSV (CH₄+C₃H₈+N₂)=600cm³g^-1h^-1 with CH₄/C₃H₈ molar ratio =5.0.The effects of preparation methods were also investigated. It was found that the activity of catalysts prepared by complex ion-exchange was higher than that of catalysts prepared by impregnation or normal ion-exchange.The influence of different methods and modified metals on surface acidity was investigated by NH3-TPD. The results indicated that complex ion-exchange can decrease the amount of strong acid sites and increase that of weak acid sits. The latter is the main active center in the aromatization of mixed methane and propane.DTAn UV-Raman and TPO/TPH were used to characterize the depoited coke on the catalysts, there are three kinds of carboneous species depoited on the catalysts after aromatization. The amount of the carboneous species is different as different preparation methods. The main carboneous species is CHx active intermediate on the catalysts prepared by complex ion-exchange, and it can be translated to products and can be eliminated in regeneration process.