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

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.