Low-Temperature Thermocatalytic Coupling of CH4 and CO2 to Ethanol over Zn–Ce/ZSM-5 by a Stepwise Technique

Abstract

Direct thermocatalytic coconversion of CH₄ and CO₂ to C₂ oxygenates at low temperatures has attracted extensive attention but is challenged due to being thermodynamically unfavorable. Herein, we report the direct coupling of CH₄ and CO₂ to ethanol as the sole liquid product on the Zn–Ce/ZSM-5 catalyst by a two-stepwise technique at 150 °C. The unexpected results toward ethanol are attributed to the special technique and Zn–O–Ce interfaces, which ensure the preferential adsorption and dehydrogenation of CH₄ on ZnOH⁺ sites, while CO₂ is adsorbed on the oxygen vacancies of Ce sites. It is found that the formation rate of ethanol is closely related to the number of medium strong acids and medium strong bases in zeolite. In situ DRIFTS experiments demonstrate that C–C is respectively realized by the coupling of CH₃* and CO₂* as well as the insertion of CO* into the CH₂* to form CH₃COO* and CH₂CO* intermediates, which undergo finally hydrogenation to achieve ethanol. This study pioneers an attractive route for the direct synthesis of ethanol from CH₄–CO₂ under mild conditions.