Mechanochemical Synthesis of Bimetallic NiCo Supported on a CeO2 Catalyst with Less Metal Loading for Non-Thermal Plasma Catalytic CO2 Hydrogenation

Non-thermal plasma (NTP) catalysis is a promising technology for CO₂ valorization with renewable H₂, in which catalyst design is one of the key aspects to progress the hybrid technology. Herein, bimetallic NiCo supported on CeO₂ catalysts, that is, NiCo/CeO₂, were developed with less metal loading of ∼2 wt % using mechanochemical synthesis for NTP-catalytic CO₂ methanation. During the synthesis, different addition orders of Ni and Co precursors were investigated, and the results show that the NiCo₁/CeO₂-I catalyst (which was prepared by the simultaneous addition of Ni and Co precursors, protocol I) exhibited the highest CO₂ conversion (∼60%) and CH₄ selectivity/yield (∼80%/∼50%), whereas the NiCo₁/CeO₂-II and NiCo₁/CeO₂-III catalysts (prepared by sequential addition protocols of II and III) showed very poor catalytic performance. Characterization results suggested that in protocol I, Ni and Co prefer to alloy, and concentrated oxygen vacancies on the CeO₂ surface and high surface basicity are retained as well. Such properties of NiCo₁/CeO₂-I were responsible for CO₂ activation and hydrogenation under NTP conditions, which was explained by the proposed mechanisms.