Redox Cycling and Restructuring of Silica‐Supported Bismuth Molybdate Catalysts

Abstract This study investigates the impact of redox‐induced bulk and surface restructuring on the catalytic behavior of unsupported and silica‐supported α‐bismuth molybdate (Bi 2 Mo 3 O 12 ). Using X‐ray photoelectron spectroscopy (XPS) and density functional theory (DFT), we observe facile reduction of Mo⁶⁺ to Mo⁵⁺/Mo⁴⁺ associated with the formation of hydroxyls and oxygen vacancies, respectively. In supported samples, XPS and X‐ray absorption spectroscopy (XAS) reveal the formation of a disordered Magnéli phase, accompanied by reduction of bismuth oxide to metallic Bi and sub‐stoichiometric oxides, with surface Bi enrichment during the first reductive cycle. These changes are largely reversible upon reoxidation; however, the surface becomes progressively less reducible, indicating restructuring toward a more stable composition. In contrast, unsupported Bi 2 Mo 3 O 12 exhibits a significant loss of surface reducibility after the first cycle, despite bulk phase changes being fully reversible, as shown by X‐ray diffraction (XRD). The silica‐supported catalyst undergoes more pronounced and continuous surface and bulk restructuring with cycling. Catalytic tests indicate that the higher acrolein selectivity and surface‐area‐normalized activity of the supported samples result from more dispersed redox‐active sites and enhanced oxygen mobility. These findings demonstrate that repeated redox cycling dynamically evolves the surface structure of α‐Bi 2 Mo 3 O 12 , ultimately stabilizing into a highly active catalytic state.