Promotional role of Ni photodepositing on Ru confined TiO2 nanotubes catalyzed CO2 methanation

Transforming CO2 into valuable chemicals and fuels via hydrogenation receives excellent concern, considering the severe environmental problems caused by CO2 emissions. However, the development of catalytic materials for low-temperature CO2 hydrogenation remains challenging. Herein, we construct a nanotube (NT) catalyst system, where Ru is confined in TiO2 nanotubes (Ru@TiO2NTs), which are further modified by Ni photodeposition (Ru@TiO2NTs–Ni). This system aims to enhance CO2 methanation by modulating the confinement effect. Ru@TiO2NTs–Ni exhibits better low-temperature catalytic activity than Ru@TiO2NTs. Approximately 86 % CO2 conversion and 100 % CH4 selectivity are achieved at 220 °C, and no decrease in catalyst activity is observed in 110 h. The interactions between Ni, Ru, and TiO2 NTs are investigated in depth using characterization techniques, such as extended X-ray absorption fine structure and in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The results indicate that part of Ni is embedded in the surface lattice of the TiO2 NTs, resulting in a large amount of Ni3+. The presence of Ni3+ causes oxygen vacancies on the surface of the nanotube and enhances the electron-deficient state inside the nanotube, thereby improving the performance of low-temperature CO2 methanation. In situ DRIFTS results indicate that the presence of Ni considerably enhances the ability of Ru to dissociate CO2 and improves CO2 methanation performance at low temperatures. This study advances the understanding of the confinement effect of TiO2 NTs and presents an approach to design efficient catalysts by modifying their electronic state, thereby providing novel insights into CO2 utilization.