The synergy of Ni doping and oxygen vacancies over CeO2 in visible light-assisted thermal catalytic methanation reaction

The photo-assisted thermal catalytic system has provided a new alternative way to drive highly efficient CO2 methanation reaction. In this work, we investigated the role of visible light for thermal catalytic methane synthesis, emphasizing the synergy effect of Ni doping and oxygen vacancies for the hydrogenation of CO2 over Ni-CeO2 catalysts. It was found that the optimal 7.5 wt% Ni-CeO2 catalysts exhibited the best visible light-promoted CO2 methanation performance. At 250 °C, the light-promoted performance increased from 0.67 to 0.93 mmol−1·g−1·h which increased by 39 %. Extensive characterization demonstrates that heteroatom Ni doping increases the content of oxygen vacancies which narrows the band gap and improves the electron density of the catalyst, resulting in accelerating the transformation of carbonate and CO intermediate species which is beneficial to yield CH4. Furthermore, the visible-light-induced regeneration of oxygen vacancies also provides more active site to facilitate the adsorption and activation of CO2 which co-promoted the photo-assisted thermal catalytic CO2 methanation reaction. The synergy effect of Ni doping and oxygen vacancies provide a new strategy to design a high-efficiency photo-assisted thermal catalyst.