Unveiling the\nRole of Strong Metal–Support\nInteractions in Gold-Catalyzed CO Oxidation on MnO<sub>2</sub> Polymorphs

The effectiveness of gold (Au)-based catalysts in CO\noxidation\nis significantly influenced by strong metal–support interactions\nwith surface oxygen structures, the mechanisms of which remain elusive.\nTo investigate this property, we selected γ-MnO<sub>2</sub>,\nfeaturing Mn(-O-)<sub>2</sub>Mn and Mn–O–Mn structural\nmotifs, and β-MnO<sub>2</sub>, characterized by Mn–O–Mn\nlinkages, as support materials. The CO oxidation process was investigated\nby fabricating Au nanoparticles supported on these two MnO<sub>2</sub> polymorphs. Our findings reveal that Au supported on β-MnO<sub>2</sub> substantially enhanced CO oxidation, in stark contrast to\nthe inhibitory effect observed with Au on γ-MnO<sub>2</sub>.\nUsing operando diffuse reflectance infrared Fourier transform spectroscopy\ncoupled with mass spectrometry, we detected an increase in the production\nof surface-adsorbed oxygen following Au deposition on β-MnO<sub>2</sub>. Conversely, Au supported on γ-MnO<sub>2</sub> resulted\nin a diminished capacity for surface oxygen adsorption. The presence\nof Au<sup>+</sup> and Mn<sup>2+</sup> ions was identified as pivotal\nfor CO oxidation. Moreover, the engagement of the Mn(-O-)<sub>2</sub>Mn structure in the reaction was impaired after Au loading on γ-MnO<sub>2</sub>, and the regeneration of the Mn–O–Mn linkage\nwas similarly hindered. We propose a mechanism for the interactions\nbetween Au and the oxygen species associated with Mn(-O-)<sub>2</sub>Mn and Mn–O–Mn structures on MnO<sub>2</sub>, offering\ninsights into the divergent catalytic behaviors exhibited by different\nMnO<sub>2</sub> polymorphs.