NO adsorption and decomposition on La 2O 3 studied by DRIFTS

Abstract

In situ diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS) was performed to study the reaction mechanism of NO decomposition on La 2O 3. Peak assignments were verified by establishing isotope shifts of species formed after adsorption of 15 NO . Peak deconvolution was employed to resolve complex spectra. The adsorption behavior of NO was established at 298 K as well as temperatures up to 773 K. Upon adsorption at room temperature, NO −, N 2O 2− 2, chelating NO − 2, nitrito (NO − 2), and unidentate and bidentate NO − 3 groups are observed, whereas at higher temperatures, nitrate and smaller amounts of NO − 2 groups prevail. A surface reaction model developed on the basis of the solid-state properties of La 2O 3 reveals that the anionic NO species (NO −, N 2O 2− 2) are formed by adsorption on anion vacancies and that they decompose at higher temperatures to yield nitrogen and oxygen. NO adsorption onto basic oxygen anion creates NO − 2 and NO − 3 spectator species; however, NO − 2 groups may also be involved in the decomposition process by reacting with the remaining oxygen to form nitrates. The surface reaction model is in agreement with a sequence derived from kinetic modeling.