Decoration of Gold and Platinum Nanoparticle Catalysts by 1 nm Thick Metal Oxide Overlayer and Its Effect on the CO Oxidation Activity

Exfoliated M–Al layered double hydroxide (M–Al LDH; M = Mg, Co, Ni, and Zn) nanosheets were adsorbed on Au/SiO₂ and calcined to transform LDH into mixed metal oxides (MMOs) and yield Au/SiO₂ coated with a thin MMO overlayer. These catalysts showed a higher catalytic activity than pristine Au/SiO₂. In particular, the 50% CO conversion temperature decreased by more than 250 °C for Co–Al MMO-coated Au/SiO₂. In contrast, the deposition of CoAlO_x on Au/SiO₂ by impregnation or the deposition of Au on Co–Al MMO-coated SiO₂ resulted in a worse catalytic activity. Moreover, the presence of a thick MMO overlayer decreased the catalytic activity, suggesting that the control of the overlayer thickness to less than 1 nm is a requisite for obtaining a high catalytic activity. Moreover, the thin Co–Al MMO overlayer on Au/SiO₂ possessed abundant oxygen vacancies, which would play an important role in O₂ activation, resulting in a highly active interface between Au and the defect-rich MMO on the Au NP surface. Finally, this can be applied to Pt/SiO₂, and the obtained Co–Al MMO-coated Pt/SiO₂ also exhibited a much improved catalytic activity for CO oxidation.