Formation of Au–MnOx Interfacial Sites on Au/SiO2 by Manganese Oxide Nanosheet Coating for Enhancement of CO Oxidation Activity

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Manganese oxide nanosheets (MNS) were used for surface modification to improve the catalytic performance of Au/SiO2 for CO oxidation. Exfoliated MNS was deposited onto Au/SiO2 and subsequently calcined at 400 °C to form MnOx-modified Au/SiO2 catalysts. Structural characterization showed that Mn species were highly dispersed and an overlayer with thickness below 1 nm was formed on the gold nanoparticles. The average gold particle size increased only slightly after the coating and calcination processes, from 5.8 nm ± 2.7 nm for pristine Au/SiO2 to 7.8 nm ± 2.4 nm for MnOx-modified Au/SiO2 after calcination. Pristine Au/SiO2 showed very low activity for CO oxidation, with only about 20 % CO conversion even at 300 °C, whereas MnOx-modified Au/SiO2 exhibited markedly enhanced activity, with CO oxidation starting at 50 °C, and a full conversion was achieved at 150 °C. The temperature at 50 % CO conversion (T50) decreased by more than 200 °C compared with pristine Au/SiO2. Diffuse reflectance infrared Fourier transformed infrared spectroscopy indicated strengthened electronic interaction between the gold particles and MnOx after calcination, suggesting the formation of close Au–MnOx interfacial contact structure. This nanosheet-coating approach provides an effective route to improve the catalytic performance of inert oxide-supported gold catalysts.

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