Direct coupling of CH4 and CO2 to acetic acid over Pd/LDH catalyst by stepwise technique

Abstract

Directly convert CH₄ and CO₂ into acetic acid is a 100 % atomic efficiency reaction, but remains a great challenge under mild conditions. Herein, we report that acetic acid is generated as the sole liquid product by direct CH₄ and CO₂ coupling over Pd/LDH catalyst by two stepwise technique at 200 °C and atmospheric pressure. The formation of acetic acid is closely related to the surface Pd⁰ content, as well as the number of medium-strong acid and medium-strong base on the catalyst surface. The results of in-situ DRIFTS experiments show that acetic acid is mainly formed by the coupling of CH₃* and CO₂* (CH₃*+CO₂*→CH₃COO*+*), or via CH_x* and COOH* coupling (CH_x*+COOH*→CH_xCOOH*+*) to form acetate which then followed by hydrogenation reaction. In which CH₃* is originated from CH₄ dehydrogenation step, and COOH* may be formed by the reduction of CO₂ on metallic Pd sites. This study provides a feasible approach for the construction of high selectivity catalytic materials for the direct co-conversion of CH₄ and CO₂ into acetic acid at low temperature.