Tailoring the oxidation state of metallic TiO through Ti3+/Ti2+ regulation for photocatalytic conversion of CO2 to C2H6

Abstract

The regulation and stabilization of the oxidation state to promote the conversion of CO2 to C2 fuel still faces many challenges. Based on the principle of charge balance, we creatively propose a co-doping strategy to adjust the surface oxidation state distribution of metallic catalysts. A TiO-based photocatalyst co-doped with Zn and N was synthesized by ammonia assisted one-step calcination method, named ZN-TC. XPS characterization shows that Zn and N adjust the valence states of adjacent Ti elements respectively, so that the surface of TiO maintains a relatively stable Ti3+/Ti2+ ratio. Under visible light irradiation, the material can catalyze CO2 into CO (324.11 μmol·g−1·h−1) and C2H6 (10.27 μmol·g−1·h−1) in the liquid phase. The selectivity of C2H6 reached 14.45%. When irradiated with near-infrared light, ZN-TC shows 100% CO selectivity because the photon energy is not enough to support the catalytic hydrogenation of CO2. Theoretical calculations and experiments proved that Zn and N elements mainly act on the B-1 band to regulate the Ti valence state. In-situ DRIFTS and in-situ Raman tests confirmed the function of oxidation state adjustment to promote the C-C coupling on the catalyst surface to produce ethoxy groups, which ultimately led to the production of C2H6.