Chemical investigation of the NOx detection mechanisms by semiconductor metal oxide nanoparticles

International audienceThis work reports an FTIR study of the NOx adsorption/desorption cycles on tin oxide nanosized particles under the operating conditions of real sensors (150 degrees C, in presence of O-2). The chemical reactions are monitored in situ and correlated with the variations of the SnO2 electrical conductivity. On the basis of the FTIR spectra, two contributing mechanisms for the NOx detection are suggested. The first one presents the formation of bridged nitrate groups bound to the SnO2 surface via oxygen vacancies acting as electron donor sites. The second mechanism also involves surface oxygen vacancies in the coordination of NOx, but this time the formation of NOx- anionic species is considered. Both mechanisms lead to the decrease of the electrical conductivity under NOx adsorption. However, the bridged nitrate groups are not reversible under gas desorption and thus irreversibly contaminate the surface after the first NOx adsorption. On the contrary, the nitrosyl anionic species are reversible and, from the second NOx adsorption/desorption cycle, ensure the reproducibility of the sensor response