Photocatalytic CO2 reduction with H2 as reductant over copper and indium co-doped TiO2 nanocatalysts in a monolith photoreactor

• Copper- and indium-co-doped TiO2 monolithic catalysts tested for CO2 reduction with H2.
• Monolith photoreactor showed efficient CO2 reduction to CO through RWGS reaction.
• CO yield over Cu–In/TiO2 was 3.23 times higher than In/TiO2 and 113 times than TiO2.
• Quantum efficiency in monolith photoreactor was much larger than cell-type reactor.
• The stability of monolithic catalysts for CO production partially reduced after third run.

The photocatalytic CO2 reduction with H2 over copper (Cu) and indium (In) co-doped TiO2 nanocatalysts in a monolith photoreactor has been investigated. The catalysts, prepared via modified sol–gel method, were dip-coated onto the monolith channels. The structure and properties of nanocatalysts with various metal and co-metal doping levels were characterized by XRD, SEM, TEM, N2 adsorption–desorption, XPS, and UV–vis spectroscopy. The anatase-phase mesoporous TiO2, with Cu and In deposited as Cu+ and In3+ ions over TiO2, suppressed photogenerated electron–hole pair recombination. CO was the major photoreduction product with a maximum yield rate of 6540 μmol g−1 h−1 at 99.27% selectivity and 9.57% CO2 conversion over 1.0 wt% Cu–3.5 wt% In co-doped TiO2 at 120 °C and CO2/H2 ratio of 1.5. The photoactivity of Cu–In co-doped TiO2 monolithic catalyst for CO production was 3.23 times higher than a single ion (In)-doped TiO2 and 113 times higher than un-doped TiO2. The performance of the monolith photoreactor for CO production over Cu–In co-doped TiO2 catalyst was 12-fold higher than the cell-type photoreactor. More importantly, the quantum efficiency of the monolith photoreactor was significantly improved over Cu–In co-doped TiO2 nanocatalyst using H2 as a reductant. The stability of the monolithic Cu–In co-doped TiO2 catalyst for CO partially reduced after the third run, but retained for hydrocarbons.

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