Synthesis of monocarboxylic acids via direct CO₂conversion over Ni-Zn intermetallic catalysts

The direct conversion of CO2 to methane, gasoline-to-diesel range fuels, methanol, and light olefins using sustainable hydrogen sources is considered a promising approach for mitigating global warming. Nevertheless, the direct conversion of CO2 to high value-added chemicals, such as acetic acid and propionic acid (AA and PA, respectively), has not been explored to date. Herein, we report a Ni-Zn intermetallic/Zn-rich NixZnyO catalyst that directly converted CO2 to AA and PA with an overall selectivity of 77.1% at a CO2 conversion of 13.4% at 325 °C. The surface restructuring of the ZnO and NiO phases during calcination and subsequent reduction led to the formation of a Ni-Zn intermetallic on the Zn-rich NixZnyO phase. Surface-adsorbed (∗CHx)n species were formed via the reverse water gas shift reaction and subsequent CO hydrogenation. Afterward, monocarboxylic acids were produced via the direct insertion of CO2 into the (∗CHx)n species and subsequent hydrogenation. The synthesis of monocarboxylic acid was highly stable up to 216 h on-stream over the Ni-Zn intermetallic catalyst, and the catalyst maintained its phase structure and morphology during long-term CO2 hydrogenation. The high selectivity toward monocarboxylic acids and high stability of the Ni-Zn intermetallic demonstrated its high potential for the conversion of CO2 into value-added chemicals.