Revealing the anti-sintering phenomenon on silica-supported nickel catalysts during CO₂ hydrogenation

The CO₂ catalytic hydrogenation represents a promising approach for gas-phase CO₂ utilization in a direct manner. Due to its excellent hydrogenation ability, nickel has been widely studied and has shown good activities in CO₂ hydrogenation reactions, in addition to its high availability and low price. However, Ni-based catalysts are prone to sintering under elevated temperatures, leading to unstable catalytic performance. In the present study, various characterization techniques were employed to study the structural evolution of Ni/SiO₂ during CO₂ hydrogenation. An anti-sintering phenomenon is observed for both 9% Ni/SiO₂ and 1% Ni/SiO₂ during CO₂ hydrogenation at 400°C. Results revealed that Ni species were re-dispersed into smaller-sized nanoparticles and formed Ni⁰ active species. While interestingly, this anti-sintering phenomenon leads to distinct outcomes for two catalysts, with a gradual increase in both reactivity and CH₄ selectivity for 9% Ni/SiO₂ presumably due to the formation of abundant surface Ni° from redispersion, while an apparent decreasing trend of CH₄ selectivity for 1% Ni/SiO₂ sample, presumably due to the formation of ultra-small nanoparticles that diffuse and partially filled the mesoporous pores of the silica support over time. Finally, the redispersion phenomenon was found relevant to the H₂ gas in the reaction environment and enhanced as the H₂ concentration increased. This finding is believed to provide in-depth insights into the structural evolution of Ni-based catalysts and product selectivity control in CO₂ hydrogenation reactions.