Creation of CuOx/ZSM-5 Zeolite Complex: Healing Defect sites, Boosting Acidic Stability and Catalytic Activity
Modifying zeolite with metal by conventional method (i.e. impregnation) could produce extra Lewis acidic species (LAS) but at the expense of intrinsic Brønsted acidity (BAS), which affects acid catalytic capability and meanwhile other inherent problems such as metal leaching, sintering and framework Al removal are sticky issues. In this work, a simple and effective method was carried out to synthesize CuOx/ZSM-5 complex (designed as Z-CuO) by directly transforming CuO nanoparticles into ZSM-5 zeolite in the cluster form. The benefits of CuOx clusters in zeolite to acidic structure and stablity of ZSM-5 zeolite are demonstrated, showing excellent performance in cracking hexane reaction. Specifically, nano CuO can be hydrothermally disintegrated into CuOx clusters, connecting with the defective silanols inside zeolite. The doped CuOx clusters in ZSM-5 zeolite can generate an extra LAS without lessening its intrinsic strong BAS, improve acidic and structural stability, due to healing the defective sites, and also protect framework Al from removal. In turn, Z-CuO complex enhances stability of CuOx clusters with no Cu leaching and sintering under high temperature reaction and catalyst regeneration. Finally, Z-CuO performs superhigh hexane conversion, high selectivity to light olefins and long catalytic lifetime, due to the stable BAS, the defect healing in Z-CuO coupled with extra LAS, leading to suppression of coke deposition.