Unveiling the Role of Strong Metal-Support Interactions in Gold-Catalyzed CO Oxidation on MnO₂ Polymorphs

The effectiveness of gold (Au)-based catalysts in CO oxidation is significantly influenced by strong metal-support interactions with surface oxygen structures, the mechanisms of which remain elusive. To investigate this property, we selected γ-MnO₂, featuring Mn(-O-)₂Mn and Mn-O-Mn structural motifs, and β-MnO₂, characterized by Mn-O-Mn linkages, as support materials. The CO oxidation process was investigated by fabricating Au nanoparticles supported on these two MnO₂ polymorphs. Our findings reveal that Au supported on β-MnO₂ substantially enhanced CO oxidation, in stark contrast to the inhibitory effect observed with Au on γ-MnO₂. Using operando diffuse reflectance infrared Fourier transform spectroscopy coupled with mass spectrometry, we detected an increase in the production of surface-adsorbed oxygen following Au deposition on β-MnO₂. Conversely, Au supported on γ-MnO₂ resulted in a diminished capacity for surface oxygen adsorption. The presence of Au⁺ and Mn²⁺ ions was identified as pivotal for CO oxidation. Moreover, the engagement of the Mn(-O-)₂Mn structure in the reaction was impaired after Au loading on γ-MnO₂, and the regeneration of the Mn-O-Mn linkage was similarly hindered. We propose a mechanism for the interactions between Au and the oxygen species associated with Mn(-O-)₂Mn and Mn-O-Mn structures on MnO₂, offering insights into the divergent catalytic behaviors exhibited by different MnO₂ polymorphs.