CO2 assisted ethane dehydrogenation over Co-exchanged ZSM-5 and ZSM-11 zeolites: Effect of Al spatial distribution

A series of cobalt catalysts loaded on ZSM-5 and ZSM-11 zeolites with different aluminum spatial distribution were prepared by wet ion-exchanged method and characterized by XRD, N-2 adsorption, SEM, Al-27 MAS NMR, H-2-TPR, Py-IR, XPS and diffuse reflectance UV-vis. Their catalytic performance in CO2 assisted dehydrogenation of ethane to ethylene has been evaluated. These catalysts display both superior activity and selectivity, with maximum ethane conversion of 51.3% and ethylene yield of 46.3%. Characterization results show that the excellent catalytic performance results from the high dispersion of cobaltous species stabilized on the exchange sites of zeolitic framework, which is positive correlated with the amount of divalent Co ions located in the internal channels (i.e. alpha-type and gamma-type). The promotional effect of CO2 on stability can be attributed to the removal of coke deposition through Boudouard reaction. The activity is not enhanced by CO2 since the reverse water-gas shift reaction is not evident here.