Direct coupling of CH4 and CO2 into acetic acid over CuPdO2/Al2O3 in the presence of H2O2
Direct conversion of methane and carbon dioxide into acetic acid is a dream way to address the two greenhouse gases, but is challenged by their chemical inertness. Cu and Pd are promising candidates both in CH 4 and CO 2 activation as well as the subsequent C-C coupling reactions at low temperature. Herein, we report that acetic acid can be produced by the direct coupling of CH 4 and CO 2 in the presence of H 2 O 2 over Cu-Pd/Al 2 O 3 catalysts at 50 °C. Results show that the acetic acid yield reaches 48.1 μmol·g cat −1 ·h −1 on the optimized reaction condition over Cu 3.8 -Pd 1.6 /Al 2 O 3 catalyst, which is higher than that of either mono-Cu or mono-Pd catalyst. Extensive characterization indicates the higher activity of Cu 3.8 -Pd 1.6 /Al 2 O 3 catalyst is attributed to the strong synergistic effect between Cu and Pd, which results in the formation of CuPdO 2 phase, and thus promoting the electron transfer from Cu to Pd. DRIFTS experiments reveal that acetic acid is produced by the coupling of CH 3 * and COOH* over CuPdO 2 active sites via Langmuir-Hinshelwood mechanism, where CH 3 * is originated from CH 4 dehydrogenation step, and COOH* may formed by the activation of CO 2 by H 2 O 2 . This study provides a new approach for the co-conversion of CH 4 and CO 2 into acetic acid at low temperature.
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