Abstract: Therecent advances in the characterization of active phase structures in hydrodesulfurization (HDS) catalysts using infrared (IR) spectroscopy are comprehensively reviewed. Particular emphasis is placed on the application of probe molecules (CO, NO) to elucidate the morphological and electronic features of key active phases, including MoS₂, CoMoS, NiMoS, and NiWS. Critical structural characteristics such as Mo edge (M-edge), S edge (S-edge), and coordinatively unsaturated sites (CUS), along with their established correlations with desulfurization performance, are systematically analyzed. The influences of catalyst supports, promoting elements, and synthesis conditions on the formation and distribution of these active phases are examined. Furthermore, the significant advantages of in situ IR spectroscopy in probing dynamic structural reconstruction and elucidating reaction mechanisms are highlighted. Current limitations, notably spatiotemporal resolution constraints under reaction conditions, are addressed. Future research directions involve leveraging advanced spectroscopic tools and machine-learning-assisted data analysis to achieve precise mapping of active phase structures, thereby laying the groundwork for the rational design of next-generation high-performance HDS catalysts.

Key words: hydrodesulfurization, catalyst, probe molecule, adsorption, active phase structure, in situ infrared spectroscopy