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

Abstract

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.