PNNL

Abstract

The interaction of N2O with oxygen vacancies (VO’s) on a partially-reduced rutile TiO2(110)-1×1 surface was investigated using temperature-programmed desorption (TPD). Contrary to a common belief that VO on a rutile TiO2(110) is a dissociation site for N2O, our results indicate that N2O does not dissociate to form N2(g) and O(a). In TPD, N2O desorption shows two peaks with maxima at 135 and 175 K that are assigned to N2O desorption from Ti4+ and VO sites, respectively, with absolute coverages determined to be 5.1 × 1014 N2O/cm-2 and 2.6 × 1013 cm-2, respectively. When VO’s are passivated by dissociative adsorption of H2O, the N2O desorption peak at 175 K disappears, evidencing that the peak is related to VO-bonded N2O. The absence of N2O dissociation on VO’s is supported by a number of observations. First, the integrated amount of N2O desorbed from the substrate during TPD vs. the amount of N2O dosed at 70 K shows a straight line with no offset indicating no loss of N2O due to the N2 formation. Second, N2O scattering experiments at 300 - 350 K indicate no change in the VO concentration as determined from the H2O TPD spectra. Third, N¬2O uptake experiments at 70 - 90 K show that the N2 desorption feature is observed from TiO2(110) surfaces without VO’s, suggesting a possible contribution from background N2 adsorption. Based on the above observations, we conclude that N2O does not dissociate on VO sites on TiO2(110) in contrast with the currently accepted view.