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 CO 2 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 (TiO 2 ) and analyzing their performance. Comprehensive characterization techniques, including electron microscopy, confirmed the uniform dispersion of metal atoms on TiO 2 . Among the catalysts, Ir/TiO 2 exhibited the best results, achieving an 84 % CO 2 conversion rate and ∼98 % CO selectivity, surpassing Pd/TiO 2 and Ru/TiO 2 , which gained 56 % and 52 % conversion, respectively. In-situ gas transmission electron microscopy revealed the catalytic behavior of Ir/TiO 2 , 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/TiO 2 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. • Successful and reproducible synthesis of thermally stable M/TiO 2 single-atom catalysts with 0.05 % metal loading using modified adsorption method. • Demonstration of exceptional performance, achievement of nearly 100 % CO selectivity with a high conversion rate of 84 % at 700 °C during CO 2 hydrogenation. • Nanoscale observations of synthesized M/TiO 2 catalysts in gaseous environments and real-time with in-situ gas transmission electron microscopy. • Validation of experimental findings with density functional theory methods.