03/01627 Chemical characteristics of coke on Mo/HZSM-5 catalysts for methane dehydroaromatization under nonoxidative conditions by TP techniques: Liu, H.-M. et al. Gaodeng Xuexiao Huaxue Xuehao, 2002, 23, (8), 1556–1561. (In Chinese)

Abstract

Over Mo/HZSM 5 catalysts, various carbonaceous depositions occurred during the course of methane dehydroaromatization(MDA). These species of surface carbon formed on HZSM 5 zeolite or Mo/HZSM 5 catalysts with different Mo loadings were investigated by means of TPH, TPCO 2 and TPO in combination with thermal gravimetric analysis(TG). The results of TG revealed that, the total amount of coke formed on 6Mo/MCM 22 during TPSR is larger than those formed on HZSM 5 zeolite, 2Mo/HZSM 5 and 10Mo/HZSM 5 catalysts. The TPO profiles recorded during the procedure of coke burning off show two different temperature peaks. The results of TPO and TG after TPH suggested that, the TPH experiments only had an effect on the coke burnt off at a high temperature, but didn′t result in the diminishing of the coke burnt off at low temperature peak. On the other hand, the result of the coked catalyst after succeeding TPCO 2 experiments exhibited an obvious reduction in the areas of both the high and low temperature peaks, particularly in the area of the low temperature peak. The study on the catalysts with different Mo loadings suggested that, the percentage of the coke burnt off at a low temperature turned larger with the increase of Mo loading, respectively. And the change trend of the coke burnt off at a high temperature was opposite exactly. By using the experiments of TPSR, TPH, TPCO 2 and TG, quantitative analysis of the coke and the kinetics of its burning off process have been done. The results show that, either TPH or TPCO 2 can diminish the starting temperature and decrease the activation energy, and there are some differences among the catalysts with various Mo loadings.