Computational study on the catalytic cycle for reduction of NO to N2 catalyzed by a ruthenium–substituted Keggin-type polyoxometalate

Abstract

Reaction mechanism corresponding to reduction of NO to N2 by hydroxylammonium chloride (NH2OH⋅HCl) catalyzed by a ruthenium–substituted Keggin-type polyoxometalates (POMs) has been studied by using density functional theory (DFT) method with the M06L functional. A complete catalytic cycle including adsorption of reactant, activation of the hydroxylammonium chloride, formation of hyponitrous acid intermediates ((HNO)2), removal of water molecules to generate N2, has been proposed based on our mechanism study. The key intermediate (HNO)2 toward N2 is identified. The Ru center in this POM complex is proposed to be the active site, responsible not only for the formation of (HNO)2 by the reaction of NO and NH2OH⋅HCl but also for the subsequent two dehydration steps to form N2, which is well in agreement with available experimental literature. The calculated whole energy profiles indicate that the formation of dinitrogen is controlled by thermodynamic factor. Detailed electronic structure analysis indicates that the coordinated NO is a good electrophile and responsible for the catalytic activity because the Ru → NO+ back donating bonding interaction. These results provide a valuable insight to development of the redox catalyst of NO into inorganic POM field.