UV to IR Continuous Photocatalytic Gas-Phase CO₂ Hydrogenation Over Ni-Doped Molybdenum Oxysulfide: An Experimental and Mechanistic Study

The reduction of CO₂ toward CO and CH₄ over Ni-loaded MoS₂-like layered nanomaterials is investigated. The mild hydrothermal synthesis induced the formation of a molybdenum oxysulfide (MoO_xS_y) phase, enriched with sulfur defects and multiple Mo oxidation states that favor the insertion of Ni²⁺ cations via photo-assisted precipitation. The photocatalytic tests under LED irradiation at different wavelengths from 365 to 940 nm at 250°C rendered 1% CO₂ conversion and continuous CO production up to 0.6 mmol/(g_cat h). The incorporation of Ni into the MoO_xS_y structure boosted the continuous production of CO up to 5.1 mmol/(g_cat h) with a CO₂ conversion of 3.5%. In situ spectroscopic techniques and DFT simulations showed the O-incorporated MoS₂ structure, in addition to Ni clusters as a supported metal catalyst. The mechanistic study of the CO₂ reduction reaction over the catalysts revealed that the reverse water–gas shift reaction is favored due to the preferential formation of carboxylic species.