Boosting CO2 methanation activity by tuning Ni crystal plane and oxygen vacancy in Ni/CeO2 catalyst

It is challenging to boost CO2 methanation activity over Ni-based catalysts, and new findings that decipher the relationship between the essential laws of catalysts and their catalytic performance will be transformative. Herein, three kinds of Ni/CeO2 catalysts with different Ni crystal facets and oxygen vacancy are developed by varied preparation methods, which show significant differences in catalytic performance for CO2 methanation, and these catalysts are taken as a case study for the investigation of the crystal plane and oxygen vacancy effects in CO2 methanation as well. It is observed that the activity of Ni/CeO2-SG catalyst with abundant oxygen vacancies and principally exposed Ni (1 1 1) crystal facet is highly active for CO2 methanation reaction, which is 1–3 times than that of Ni/CeO2 catalysts with poor oxygen vacancy and/or Ni (1 1 1) crystal face. In addition, the former one cannot suffer from deactivation even in operation 130 h at 300 °C. Both structural investigations and catalytic evaluations indicate that the adsorption and activating ability of H2 and CO2 can be controlled by adjusting the Ni-exposed crystal face and oxygen vacancy concentration, respectively. It is also verified that the synergistic contribution of the Ni crystal facets and the oxygen vacancy play a crucial role in boosting the catalytic activity of the Ni/CeO2 catalysts by affecting the adsorption and activation of reactants. The Ni/CeO2 catalysts exposed Ni (1 1 1) crystal plane facilitate the catalytic activity by strengthing the H2 adsorption/dissociation capacity, while the abundantly available oxygen vacancies maximize the activity via acting as CO2 activation sites. Furthermore, the in situ DRIFT experiments reveal that the direct formate hydrogenation pathway is involved in the CO2 methanation process over the Ni/CeO2-SG catalyst.