Carbon Monoxide Oxidation by Polyoxometalate-Supported Gold Nanoparticulate Catalysts: Activity, Stability, and Temperature-Dependent Activation Properties

Nanoparticulate gold supported on a Keggin-type polyoxometalate (POM), Cs-4[-SiW12O40]nH(2)O, was prepared by the sol immobilization method. The size of the gold nanoparticles (NPs) was approximately 2nm, which was almost the same as the size of the gold colloid precursor. Deposition of gold NPs smaller than 2nm onto POM (Au/POM) was essential for a high catalytic activity for CO oxidation. The temperature for 50% CO conversion was -67 degrees C. The catalyst showed extremely high stability for at least one month at 0 degrees C with full conversion. The catalytic activity and the reaction mechanism drastically changed at temperatures higher than 40 degrees C, showing a unique behavior called a U-shaped curve. It was revealed by IR measurement that Au+ was a CO adsorption site and that adsorbed water promoted CO oxidation for the Au/POM catalyst. This is the first report on CO oxidation utilizing Au/POMs catalysts, and there is a potential for expansion to various gas-phase reactions.