Gold–indium modified TiO₂ nanocatalysts for photocatalytic CO₂ reduction with H₂ as reductant in a monolith photoreactor

Graphical abstract: - Highlights: • Gold and indium based TiO₂ monolithic catalysts tested for CO₂ reduction with H₂. • Monolith photoreactor showed efficient CO₂ reduction to CO through RWGS reaction. • CO production rate over Au–In/TiO₂ was 76 times higher than un-doped TiO₂ catalyst. • Quantum efficiency in Au–In/TiO₂ for CO was 0.79%, much higher than in literature. - Abstract: In this study, CO₂ photoreduction via reverse water gas shift (RWGS) reaction over gold (Au) and indium (In) modified TiO₂ nanocatalysts in a monolith photoreactor has been investigated. Crystalline nanoparticles of anatase TiO₂ were obtained in doped TiO₂ samples with metals deposited over TiO₂ as Au and In³⁺ ions. The catalytic performance of metal-doped/TiO₂ catalysts was found to be considerably higher when compared to pure TiO₂. The maximum production of CO as the main product was 8982 μmol g-catal⁻¹ h⁻¹ at selectivity 99% and CO₂ conversion of 9.5% over 0.2 wt.% Au–3.5 wt.% In/TiO₂, and CO₂/H₂ feed ratio 1.5. The CO production over co-metals (Au–In) doped TiO₂ monolithic catalyst was 1.3 times higher than Au/TiO₂, 4.39 times higher than In/TiO₂ and 76 times higher than un-doped TiO₂ catalysts. Significantly higher photoactivity of metal-doped TiO₂ was obviously due to fast electron transfer with hindered recombination rates and larger illuminated surface area in monolith channels. The quantum efficiency of CO production through RWGS reaction using Au–In/TiO₂ catalyst was considerably improved (0.79%) than Au/TiO₂ (0.53%) and In/TiO₂ (0.14%) monolithic catalysts. The stability of the reused catalysts for CO production sustained at cyclic runs. This development confirmed higher performance of metals-doped TiO₂ nanocatalysts supported over monolith channels for CO₂ photoreduction via RWGS reaction