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.