Efficient Stable Catalysts for Low Temperature Carbon Monoxide Oxidation

Octahedral molecular sieves (OMS), doped with Ag+, Co2+, and Cu2+, have been tested for their catalytic activity for carbon monoxide oxidation at low temperatures for long times on stream. Metal loaded OMS materials are highly active for this catalytic reaction and compare favorably with other catalysts such as Hopcalite-like CuMn2O4 catalysts, supported Ag catalysts, and supported noble-metal catalysts, especially with respect to resistance to deactivation in a long run. Co-doped OMS-2 has been tested for selective oxidation in the presence of a large surplus of hydrogen in the feed gas. This catalyst shows nearly exclusive oxidation of CO versus hydrogen with oxygen present in stoichiometric amounts with carbon monoxide. Its stability against reduction in CO or H2 containing gas is demonstrated from comparisons of X-ray diffraction patterns and X-ray photoelectron spectra before and after exposure to these gases. Average oxidation numbers and populations of Mn valence states were determined for these catalysts. Catalytic activity of doped OMS catalysts toward CO oxidation shows a correlation among average oxidation number of Mn and the position and nature of the doped cation. The structure of the active sites and the mechanism of the reaction are proposed.