Investigation of titania and ceria support effects in nickel catalyzed CO2 methanation†

Ni catalysts, supported on TiO₂ or CeO₂, are active and selective for CO₂ methanation. To investigate the role of the support on the resulting Ni structure and catalytic performance, catalysts were prepared by strong electrostatic adsorption, incipient wetness impregnation, and colloidal nanoparticle synthesis. The reactivity follows a volcano-type trend with Ni particle size on both TiO₂ and CeO₂ supports. To explain this trend, the role of the support on the reducibility of the Ni particles and distribution of basic sites on CO₂ methanation activity was investigated. Using in situ infrared spectroscopy, we found that on TiO₂ supported catalysts with larger Ni particles, CO₂ methanation proceeds via a CO intermediate and the highest activity was observed when CO₂ methanation occurs through both CO and carbonate intermediates. For catalysts with smaller particles on TiO₂, however, no CO intermediates are observed, and catalytic activity is lower. For CeO₂, the methanation also proceeds via a CO intermediate, though for larger Ni particles only CO species were observed. CeO₂ without Ni can create surface formate species but has low reactivity towards methanation. In this investigation, we demonstrate a connection between the size of Ni particles, their corresponding adsorbed surface species, and their reactivity for CO₂ methanation.