Regulation of Ir Dopant in Mo Oxides by Flame Spray Pyrolysis for Efficient CO₂ Hydrogenation

Mo carbide is recognized as one of the most promising catalysts for CO₂ utilization via reverse water-gas shift (RWGS). However, the catalysts always suffered from low processing capacity, undesired products and deactivation. Herein, an Ir modified MoO₃ synthesized by the flame spray pyrolysis (FSP) method exhibits higher reaction rate (63.0 g_CO2 g_cat ^-1 h^-1) compared to the one made by traditional impregnation method (45.8 g_CO2 g_cat ^-1 h^-1) over the RWGS reaction at 600 °C. The distinguishing feature between the two catalysts lies in the chemical state and space distribution of Ir species. Ir species predominated in the bulk phase of MoO₃ during the quenching process of the FSP method and were mainly in the metallic states, which was revealed by X-ray absorption spectroscopy (XAS), X-ray photoelectron spectroscopy (XPS), and time-of-flight secondary ion mass spectroscopy (ToF-SIMS) characterizations. In contrast, the Ir introduced via the impregnation method was mainly on the surface of MoO₃ and in the oxidized state. The regulation of Ir dopant in MoO₃ catalyst by different methods determines the carbonization process from MoO₃ to Mo carbides and thus affects the catalytic performance over RWGS reaction. This work sheds light on the superiority of the FSP method in synthesizing Mo oxides with heteroatoms and further creating an efficient Mo-based catalyst for CO₂ conversion.