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-MnO 2, featuring Mn(-O-) 2 Mn and Mn–O–Mn structural motifs, and β-MnO 2, characterized by Mn–O–Mn linkages, as support materials. The CO oxidation process was investigated by fabricating Au nanoparticles supported on these two MnO 2 polymorphs. Our findings reveal that Au supported on β-MnO 2 substantially enhanced CO oxidation, in stark contrast to the inhibitory effect observed with Au on γ-MnO 2 . 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-MnO 2 . Conversely, Au supported on γ-MnO 2 resulted in a diminished capacity for surface oxygen adsorption. The presence of Au + and Mn 2+ ions was identified as pivotal for CO oxidation. Moreover, the engagement of the Mn(-O-) 2 Mn structure in the reaction was impaired after Au loading on γ-MnO 2, 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-) 2 Mn and Mn–O–Mn structures on MnO 2, offering insights into the divergent catalytic behaviors exhibited by different MnO 2 polymorphs.