One-pot hydrothermal synthesis of ZSM-5–CeO2 composite as a support for Cr-based nanocatalysts: influence of ceria loading and process conditions on CO2-enhanced dehydrogenation of ethane

Abstract

The oxidative dehydrogenation of ethane in the presence of CO₂ was investigated over a series of Cr impregnated ZSM-5–CeO₂ nanocatalysts with the aim of exploring the ceria addition effect. To this aim, ZSM-5–CeO₂ supports varying in ceria content (0, 5, 10, 15, 30 wt%) were synthesized using a one-pot hydrothermal method. The effect of ceria addition and its content on the structural properties and performance of Cr/ZSM-5 was investigated. The as-synthesized nanocatalysts were characterized by XRD, ICP, N₂ adsorption–desorption, FESEM, HRTEM, FTIR, EDX and TPR-H₂ techniques. Based on the characterization results, a decrease in α-Cr₂O₃ formation and metal particles size as well as an observable increase in the Cr dispersion and reducibility were found. However, CeO₂ doping resulted in the decrease of BET surface area. The variation of ceria content indicates that the surface area, metal dispersion, catalyst reducibility and uniformity of surface particles of samples increased with the ceria content up to 10 wt%. However, a decreasing trend and higher number of agglomerations were observed with further increase of the ceria content. The results revealed that CeO₂ addition not only enhances the catalytic activity of Cr/ZSM-5 but also makes it less sensitive to deactivation during the course of running the reaction for about 5 h. It was also observed that there is optimum ceria content in the ZSM-5–CeO₂ support containing 10% ceria for the best catalytic activity, attributable to better textural properties, smaller number of agglomerations, more uniform dispersion and more reducibility. It effectively dehydrogenated ethane to ethylene with CO₂ at 700 °C even after 5 h on-stream operation, giving 58.5% ethylene yield.