Synergistic dehydrogenation-acid site interactions in CoO_x@HZSM-5 for efficient n-butane catalytic cracking

The efficient conversion of light alkanes into high-value-added products is crucial for achieving a carbon-neutral society. Catalytic cracking of light alkanes has emerged as a promising alternative to conventional steam cracking for light olefins production and has garnered significant attention. Herein, we designed bifunctional CoO_x@HZSM-5 catalysts integrating dehydrogenation and cracking active sites. The effects of cobalt loading and Si/Al ratio on the catalytic performance of n-butane catalytic cracking were systematically investigated over CoO_x@HZSM-5, and the structure-activity relationship and reaction pathway were carefully established. A clear volcano-type relationship between the n-butane conversion/yield of ethene and propene and Co content was identified, and 1 %CoO_x@HZSM-5(Si/Al=91) exhibits the highest catalytic performance, while the catalytic activity increases with the decrease of Si/Al ratio. It is demonstrated the introduction of cobalt species into HZSM-5 contributes to increasing the dehydrogenation rate of n-butane and facilitating the formation of butene, a more reactive intermediate, thereby improving the catalytic activity. Structure-activity analysis indicates that the increased density of Lewis and Brønsted acid sites enhances the yield of ethene and propene, primarily owing to the improved conversion of n-butane, while the ratio of B/L governs the dehydrogenation-to-cracking rate. Furthermore, butene was identified as a primary coke precursor in the course of n-butane catalytic cracking. The obtained knowledge of tuning the catalytic performance and coke formation facilitates the development of efficient bifunctional catalysts, and advances the understanding of synergetic effects in heterogeneous catalysis.