Low-temperature CO oxidation by transition metal polycation exchanged low-silica faujasites

• The novel CO oxidation catalyst with a superior activity is suggested.
• Transition metal polycation clusters are responsible for the catalyst activity.
• Various mechanisms of CO oxidation have been disclosed for different catalysts.
• One of the new catalysts manifests capability for oxidizing CO without free O2.

The kinetics and mechanism of low-temperature carbon monoxide oxidation by transition metal polycation exchanged low-silica faujasite (LSF) are investigated. Single and double Cu, Zn, and Mn polycation containing samples were prepared by ion exchange with the corresponding salt solutions at the conditions of their partial hydrolysis. Catalytic tests of the prepared samples by the micro reactor method demonstrated an exceptional activity of novel catalysts in CO oxidation. Reaction kinetics measurements at gradientless conditions along with the catalysts ESR characterization and DRIFT spectroscopy of chemisorbed CO allowed to single out three different models of CO oxidation over the studied catalysts: a) the Eley–Rideal mechanism for single Zn-, Mn- and double MnCu-polycation exchanged LSF having the zero order of the reaction rate for CO and the first order for O2; b) the Mars–van Krevelen mechanism for the CuCaLSF catalyst with the reaction rate order 0.11 for CO and the zero order for oxygen; c) the autocatalytic model for CuZn-polycation exchanged faujasite that is characterized by the zero order for both reactants, CO and O2, with a capability for direct oxidation of carbon monoxide not involving free oxygen.

The DRIFT spectrum of CO chemisorbed by CuZn polycation exchanged LSF demonstrates immediate oxidation of the substrate by excessive oxygen of the polycations away from free gas phase O2. This distinguishing feature of the catalyst leads to the autocatalytic mode of CO oxidation by air with zero-rate order for both reactants, CO and O2.Figure optionsDownload as PowerPoint slide