Toward High-Value Hydrocarbon Generation by Photocatalytic Reduction of CO₂ in Water Vapor

Semiconductor crystals with well-defined morphology, porous nanostructure, and spatially separated active sites are attractive for use in photocatalysis. This paper describes a controlled synthesis of cake-like porous TiO2 photocatalyst with surface-localized doping of copper and cobalt by using a well-defined MIL-125(Ti) metal organic framework as template precursor. The series of the modified TiO2 photocatalysts present the improved activity for photocatalytic CO2 reduction with water vapor. It is found that 1%Cu-doped TiO2 shows an enhanced behavior for breaking C═O bonds. In this case, the outcomes are primarily CO and CH4, yielding up to 135.94 and 127.05 μmol, respectively, under the irradiation of simulated sunlight for 3 h. The performance can be further improved by incorporating trace cobalt. Besides the improved property for CO and CH4 production, the selectivity also shifts to high-value hydrocarbons (C2+). The yields for C2H6 and C3H8 can be up to 267.60 and 10.07 μmol, respectively, by using 0.02%Co-1%Cu/TiO2. Our in situ Fourier transform infrared spectra together with theoretical calculations indicate that efficient charge separation on copper and cobalt ions is achieved. This altered charge behavior leads to the generation and enrichment of methyl radicals on the surface of cobalt ions, giving rise to the production of C2+ hydrocarbons. This work demonstrates a vibrant catalyst platform for solar fuel generation by photocatalytic CO2 conversion in water.

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