Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
45801 | Applied Catalysis B: Environmental | 2013 | 10 Pages |
The incorporation of Cu species in TiO2 photocatalysts is critical in photocatalytic CO2 reduction to fuels, but the effect of Cu valence is poorly understood. In this work, Cu/TiO2 (P25) nanoparticle catalysts were prepared by a simple precipitation and calcination method. The as-prepared Cu/TiO2 sample was dominated by Cu2+ species. Thermal pretreatment of the as-prepared samples in He and H2 atmosphere resulted in the transition to a surface dominated by Cu+ and mixed Cu+/Cu0, respectively, confirmed by in situ X-ray photoelectron spectroscopy (XPS) and diffuse-reflectance infrared Fourier transform spectroscopy (DRIFTS) analyses. These thermal pretreatments in reducing atmospheres also induced the formation of defect sites such as oxygen vacancies and Ti3+. The various Cu/TiO2 catalysts were tested in CO2 photoreduction with water vapor under simulated solar irradiation, and their activities were in the order of as-prepared (unpretreated) < He-pretreated < H2-pretreated. Compared with unpretreated TiO2 (P25), the H2-pretreated Cu/TiO2 demonstrated a 10-fold and 189-fold enhancement in the production of CO and CH4, respectively. This significant enhancement was mainly attributed to the synergy of the following two factors: (1) the formation of surface defect sites promoting CO2 adsorption and subsequent charge transfer to the adsorbed CO2; (2) the existence of Cu+/Cu0 couples that facilitate electron and hole trapping at different sites.
Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Cu/TiO2 photocatalysts are fabricated for CO2 photoreduction with water vapor. ► Cu valence and oxygen vacancy are tailored by thermal treatment in He or in H2. ► Photo-activity in the order: H2-pretreated > He pretreated > unpretreated. ► Mixed Cu+/Cu0 promote electron–hole separation more effectively than Cu+ and Cu2+. ► CO2− species is a CO2 reduction intermediate according to in situ DRIFTS.