Characterization of Au/MnO x /TiO2 for Photocatalytic Oxidation of Carbon Monoxide

The Au/MnO _x /TiO₂ catalyst was used for the photocatalytic oxidation of carbon monoxide. The catalytic activity of Au/MnO _x /TiO₂ with low concentration of manganese (3–7 mol%) was much higher than that of Au/TiO₂. The surface of Au/MnO _x /TiO₂ was characterized by XPS and Raman spectroscopy. While the main state of manganese in 13.8 mol% MnO _x /TiO₂ was Mn⁴⁺ species, Mn³⁺ was the dominant species in the samples with below 6.5 mol% manganese. Raman spectroscopy revealed that the interaction between the MnO _x and TiO₂ form Mn–O–Ti species in which the state of manganese was Mn³⁺. The Au particles also interacted with both MnO _x and TiO₂ to modify the surface of them. In the case of the Au species, low loading of manganese produced the metallic Au⁰ and perimeter interfacial Au^δ+, whereas high loading showed the coexistence of three components which were metallic Au⁰, perimeter interfacial Au^δ+, and oxidic Au³⁺. The catalytic active component was the metallic Au⁰ and perimeter interfacial Au^δ+ species, which were dispersed on TiO₂ and Mn³⁺/TiO₂.