IR spectroscopic study of NO2 adsorption on chromia
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.