Effect of Ni particle size on the production of renewable methane from CO₂ over Ni/CeO₂ catalyst

Production of ‘renewable Methane’ has attracted renewed research interest as a fundamental probe reaction and process for CO₂ utilization through potential use in C1 fuel production and even for future space exploration technologies. CO₂ methanation is a structure sensitive reaction on Ni/CeO₂ catalysts. To precisely elucidate the size effect of the Ni metal center on the CO₂ methanation performance, we prepared 2%Ni/CeO₂ catalysts with pre-synthesized uniform Ni particles (2, 4 and 8 nm) on a high surface area CeO₂ support. Transmission electron microscopy (TEM) and ambient pressure X-ray photo spectroscopy (AP-XPS) characterization have confirmed that the catalyst structure and chemical state was uniform and stable under reaction conditions. The 8 nm sized catalyst showed superior methanation selectivity over the 4 and 2 nm counterparts, and the methanation activity in term of TOF is 10 times and 70 times higher than for the 4 and 2 nm counterparts, respectively. The DRIFTS studies revealed that the larger Ni (8 nm particles) over CeO₂ efficiently facilitated the hydrogenation of the surface formate intermediates, which is proposed as the rate determining step accounting for the excellent CO₂ methanation performance.