Nonoxidative propane dehydrogenation by isolated Co²⁺ in BEA zeolite: Dealumination-determined key steps of propane C–H activation and propylene desorption

With BEA (Si/Al = 20) zeolite and dealuminated Si-BEA as supports, the non-noble metal Co catalysts are prepared by vacuum impregnation method to study the correlation between the catalyst structure and catalytic performance in propane dehydrogenation (PDH) reaction. The optimal 0.5 wt% Co@Si-BEA catalyst exhibits over 93 % selectivity to propylene, high single-pass yield and great regeneration stability in the recycling PDH reactions at 590 °C. The isolated Co²⁺ cations are anchored in the micropores of Si-BEA zeolites through interacting with the silanol groups generated by dealumination treatment, and serve as the catalytically active sites to selectively activate the C–H bonds of propane rather than dissociate the C–C bonds. Furthermore, Co@Si-BEA catalyst adsorbs propylene in a favorable configuration, leading to desired adsorption features with respect to less amount and weaker strength in comparison with that on non-dealuminated Co@BEA catalyst. Therefore, the facile propylene desorption can be achieved on Co@Si-BEA catalyst, which is responsible for its high propylene selectivity, activity, and long-term stability in PDH reaction. By contrast, Co@BEA catalyst with higher density of surface Brønsted acid sites, facing with severe issues of propane C–C bond scission, strong propylene adsorption and coke deposition-caused deactivation.