Low-Temperature Thermocatalytic Coupling of CH<sub>4</sub> and CO<sub>2</sub> to Ethanol over Zn–Ce/ZSM-5 by a Stepwise Technique
Yongjun Liu, Zhang Chaoyu, Ruijia Wang, Yixiao Wu, Xueyu Zan, Shiqi Tao, Wei Huang
Abstract
Direct thermocatalytic coconversion of CH 4 and CO 2 to C 2 oxygenates at low temperatures has attracted extensive attention but is challenged due to being thermodynamically unfavorable. Herein, we report the direct coupling of CH 4 and CO 2 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 CH 4 on ZnOH + sites, while CO 2 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 CH 3 * and CO 2 * as well as the insertion of CO* into the CH 2 * to form CH 3 COO* and CH 2 CO* intermediates, which undergo finally hydrogenation to achieve ethanol. This study pioneers an attractive route for the direct synthesis of ethanol from CH 4 –CO 2 under mild conditions.