FTIR and density functional study of NO interaction with reduced ceria: Identification of N3− and NO2− as new intermediates in NO conversion

Abstract

To design new deNOx materials and processes we need to know in details the mechanism of NO interaction with solid surfaces. Many NOx conversion catalysts contain ceria as a component and cerium changes its oxidation state in the course of redox catalytic processes. Here we show that the interaction between NO and reduced ceria leads to formation of azides (N3−, 2044–2042cm−1) and nitric oxide dianion (NO2−, 1010–980cm−1) with the simultaneous oxidation of Ce3+. These species are established for the first time after NO adsorption on solid surfaces and their relative concentrations strongly depend on the sample morphology. At ambient temperature N3− does not interact with NO or O2 alone but easily disappears in the co-presence of the two gases, thus demonstrating reactivity similar to that of isocyanates. In contrast, NO2− accepts one NO molecule and is converted into hyponitrite (bands in the 1030–970cm−1 region). At further stages of interaction, N2O, N2, nitrites and nitrates are formed. The present findings enrich the current opinions of catalytic NO conversion and impose some revisions.