Performance analysis of nanostructured NiO-In₂O₃/TiO₂ catalyst for CO₂ photoreduction with H₂ in a monolith photoreactor

The photocatalytic reduction of CO₂ with H₂ over nickel (Ni) and indium (In) co-doped TiO₂ nanocatalysts in a monolith photoreactor has been investigated. The structure and properties of catalysts, prepared via modified sol-gel method with different metal-doping levels, were characterized by XRD, SEM, TEM, N₂ adsorption-desorption, XPS, UV-vis and PL spectrophotometry. Both nickel and indium, present over TiO₂ as Ni²⁺ and In³⁺, promoted efficient separation of photo-generated charges (e^-/h⁺). The CO₂ reduction efficiency was more significant for H₂ compared to H₂O vapors. TiO₂ modified with 1.0wt.% NiO and 3.5wt.% In₂O₃ registered the highest CO yield. In a batch process, the maximum yield rate of CO over NiO-In₂O₃/TiO₂ catalyst at 99.7% selectivity was 12,029μmolg-catal.^-1h^-1; 5.9 and 207 folds higher than In₂O₃/TiO₂ and TiO₂ catalysts, respectively. Similarly, CO₂ conversion over NiO-In₂O₃/TiO₂ (10.2%) was more substantial than In₂O₃/TiO₂ (6.42%) and pure TiO₂ (1.7%). In a continuous process, CO production rate was slightly decreased, but more CO₂ was processed over the entire irradiation time. Significantly enhanced quantum efficiency of a monolith photoreactor over NiO-In₂O₃/TiO₂ catalyst was observed compared to the cell reactor obviously due to greater mobility of charges with hindered recombination rate and higher photonic efficiency. The stability of NiO-In₂O₃/TiO₂ catalyst was partially reduced after several cyclic runs.