High-performance single-atom M/TiO₂ catalysts in the reverse water-gas shift reaction: A comprehensive experimental and theoretical investigation

Single-atom catalysts (SACs) offer high efficiency and selectivity in chemical reactions but face challenges in converting CO₂ to CO via the reverse water gas shift (RWGS) reactions. This study addresses these challenges by anchoring three noble metals (Ir, Pd, and Ru) onto titania (TiO₂) and analyzing their performance. Comprehensive characterization techniques, including electron microscopy, confirmed the uniform dispersion of metal atoms on TiO₂. Among the catalysts, Ir/TiO₂ exhibited the best results, achieving an 84 % CO₂ conversion rate and ∼98 % CO selectivity, surpassing Pd/TiO₂ and Ru/TiO₂, which gained 56 % and 52 % conversion, respectively. In-situ gas transmission electron microscopy revealed the catalytic behavior of Ir/TiO₂, showing Ir atom mobility and the formation of ∼1 nm nanoclusters. Density functional theory (DFT) and in-situ diffuse reflectance infrared spectroscopy (DRIFTs) further explained that the atomically dispersed Ir sites in Ir/TiO₂ follow a hydrogen-assisted mechanism, with the COOH* intermediate desorbing and dissociating into CO. These findings suggest SACs' potential to facilitate greener chemical processes and reduce greenhouse gas emissions.