Photo-enhanced thermal catalytic CO2 methanation activity and stability over oxygen-deficient Ru/TiO2 with exposed TiO2 {001} facets: Adjusting photogenerated electron behaviors by metal-support interactions

In this study, two Ru/TiO2 samples with different TiO2 facets were prepared to investigate their photo-thermal catalytic CO2 + H-2 reaction behavior. Without UV irradiation, the Ru/TiO2 with 67% {001} facet (3RT) displayed improved thermal catalytic activity for CO2 methanation than that of Ru/TiO2 with 30% {001} facet (0RT). After H-2 pretreatment, both samples exhibited enhanced thermal catalytic activities, but the H-2-treated 3RT (3RT-H) exhibited superior activity to that of the H-2-treated 0RT (0RT-H). Under UV irradiation, 3RT-H exhibited apparent photo-promoted thermal catalytic activity and stability, but the enhanced catalytic activity was lower than that of 0RT-H. Based on the characterization results, it is proposed that both the surface oxygen vacancies (Vos) (activating CO2) and the metallic Ru nanoparticles (activating H-2) were mainly responsible for CO2 methanation. For 0RT, H-2 pretreatment and subsequent UV irradiation did not promote the for-mation of Vos, resulting in low catalytic activity. For 3RT, on the one hand, H-2 pretreatment pro-moted the formation of Vos, which were regenerated under UV irradiation; on the other hand, the photogenerated electrons from TiO2 transferred to Ru to maintain the metallic Ru nanoparticles. Both behaviors promoted the activation of CO2 and H-2 and enhanced CO2 methanation. Moreover, the photogenerated holes favored the dissociated H at Ru migrating to TiO2, also promoting CO2 methanation. These behaviors occurring on 3RT-H may be attributed to the suitable metal-support interaction between the Ru nanoparticles and TiO2 {001}, resulting in the easy activation of lattice oxygen in TiO2 to Vos. With reference to the analysis of intermediates, a photo-thermal reaction mechanism is proposed for the Ru/TiO2 {001} facet sample. (C) 2022, Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved.