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

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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.