IR spectroscopic study of NO2 adsorption on chromia

Abstract

NO₂ adsorption on α-chromia leads to the formation of bridged and bidentate nitrates as well as of nitro species. In an NO₂ atmosphere the latter are oxidized to nitrates. When NO₂ is adsorbed with the participation of the surface hydroxy groups on chromia, bridged nitrates and water are among the reaction products. Adsorption of NO₂ on reduced samples leads to the oxidation of the surface and to the formation of the same species as observed on oxidized samples, but in different concentrations. Preadsorbed water slightly affects NO₂ adsorption. Ammonia adsorption on a sample precovered with NO₂ leads to the appearance of NH₄NO₃-like surface species (with the participation of the bridged nitrates). These species are supposed to be intermediates in the catalytic selective reduction of NO₂ by ammonia. The mechanism of the process is discussed.