Altering the influence of ceria oxygen vacancies in Ni/CexSiyO2 for photothermal CO2 methanation

Abstract

While the benefit of CeO₂ surface oxygen vacancies for CO₂ methanation is well established, their role under photothermal conditions has not been probed in depth. In this work, SiO₂ was systematically added to suppress the influence of CeO₂ surface oxygen vacancies on the reaction. Overall, a decrease in CO₂ conversion corresponded to an increase in Si composition. However, a similar level of catalytic activity was found for Ni/Ce_0.9Si_0.1O₂ and Ni/CeO₂. Unlike CeO₂, Ce_0.9Si_0.1O₂ had limited surface reducibility and restricted CO₂ interaction, indicating a lack of surface oxygen vacancies. While the photothermal catalytic activities were found to be thermally driven and comparable to the reaction under thermal conditions, the light-driven reaction does not require external heating and promotes a sustainable approach for CO₂ hydrogenation. Further study by in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) suggested catalyst activity was dictated by the vacancies' proximity to the active Ni sites rather than their relative surface abundance. The findings provide new understanding on the role of CeO₂ oxygen vacancies in catalyst performance and catalyst design for the methanation of CO₂.