Revisiting the influence of Ni particle size on the hydrogenation of CO₂ to CH₄ over Ni/CeO₂

Nickel nanoparticles were supported on CeO₂ and evaluated in the hydrogenation of CO₂ to CH₄ at 538 K and 1 atm. Chemisorption of H₂ was used to estimate the average Ni particle size, which ranged from 1.3 to 17 nm. The apparent activation energy for CH₄ formation and turnover frequency for CO₂ conversion was independent of Ni particle size. The smallest Ni particles (1.3 nm) were less selective to CH₄. Comparisons to alumina-supported Ni reveal the same performance as Ni/CeO₂ when normalized to active Ni atoms counted by H₂ chemisorption. A beneficial effect of ceria relative to alumina is the enhanced reducibility of Ni as evaluated by H₂ temperature-programmed reduction. The constancy of the turnover frequency on Ni particles suggests the acid-base and/or redox properties of the support do not play a significant role in the CO₂ methanation reaction under the conditions of study, which contrasts many earlier works.