Solution combustion synthesis of Ni-based catalyst over porous CaCO3 for plasma-catalytic CO2 methanation

To address the challenges of high energy consumption and insufficient low-temperature activity in conventional thermal catalytic CO 2 methanation, this study reports a new nickel-based catalyst preparation via the solution combustion synthesis (SCS) technique for plasma-catalytic CO 2 methanation. The results demonstrate that the SCS method successfully reconstructed the CaCO 3 support, resulting in a porous structure with a high specific surface area (23.86 m 2 /g) as well as highly dispersed Ni nanoparticles (approximately 9.32 nm), which significantly enhanced the metal-support interaction. Combined density functional theory (DFT) calculations and electron paramagnetic resonance (EPR) analysis revealed that the SCS-reconstructed CaCO 3 surface is rich in oxygen vacancies, markedly enhancing the adsorption capacity for CO 2 and CO (with adsorption energies reaching - 3.83 eV and - 3.56 eV, respectively), thereby providing favorable conditions for the intermediates formation for CO 2 conversion. Under optimized conditions (3 wt% Ni loading, H 2 /CO 2 ratio of 5, discharge power of 28 W, and gas hourly space velocity of 180,000 mL g −1  h −1 ), the CO 2 conversion reached 79.1 % with a CH 4 selectivity of 91.9 % and an energy efficiency of 17.2 %. These performance metrics are significantly superior to those of catalysts prepared by conventional impregnation methods and pure plasma systems. In situ characterizations (plasma DRIFTS and OES) indicated that the basic sites on CaCO 3 preferentially adsorb CO 2 to form carbonate species. The synergistic effect between high-energy electrons generated by the plasma and the Ni active sites promotes the hydrogenation of carbonates to formate intermediates, which are subsequently converted into CH 4 via the formate pathway (HCOO∗ → CO∗ → CH 4 or HCOO∗ → CHO∗ → CH 4 ). The catalyst exhibited good stability during a continuous 24-h operation. This study provides a novel strategy for developing a bionic synergistic catalytic system for low-temperature and highly efficient CO 2 conversion.