Electronic and Chemical Properties of Mixed-Metal Oxides: Adsorption and Reaction of NO on SrTiO₃ (100)
The interaction of NO with SrTiO (100) surfaces was investigated using thermal desorption, photoemission and first-principles density-functional calculations. The crystals used in the experiments exposed mainly (> 80%) the TiO-terminated face of SrTiO (100). On the stoichiometric surfaces, the adsorption of NO was completely reversible at submonolayer coverages. Clear peaks for desorption of NO were found at 125 (multilayer state), 160 and 260 K, plus a long tail between 300 and 450 K. Desorption of NO was detected only near 125 K with the multilayer of NO. DF calculations give adsorption energies of 14 and 6 kcal/mol for NO on the TiO- and SrO-terminated faces of SrTiO (100), which are consistent with the peaks at 260 and 160 K seen in thermal desorption. On the TiO-terminated face of SrTiO (100), there is substantial hybridization between the orbitals of NO and the oxide bands. This is not seen on the SrO-terminated face, where the large positive charge on the Sr sites leads to we ak adsorption bonds. A reaction channel for the production of NO and N is opened by partially reducing the SrTiO (100) surface. The cleavage of N-O bonds produces adatoms that quench vacancy states in the valence region and reduce the signals for Ti and Ti cations in core-level photoemission. DF calculations indicate that the adsorption of an NO single molecule over a vacancy site is a highly exothermic process (61476; 70 kcal/mol) that leads to a large elongation ({approx} 0.20) but not a complete rupture of the N-O bond. The dissociation of this bond is facilitated by the addition of a second NO molecule and formation of a ON-NO dimmer. The behavior of SrTiO illustrates the important effects that metal and oxygen metal interactions can have on the electronic and chemical properties of a mixed-metal oxide. When dealing with ABO perovkite catalysts, a simple extrapolation of the catalytic properties of the individual AO and BO oxides may not be a reliable approach.
- Research Organization:
- Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC06-76RL01830
- OSTI ID:
- 15007556
- Report Number(s):
- PNNL-SA-37280; KC0302010
- Journal Information:
- Journal of Chemical Physics, 118(14):6562-6571, Journal Name: Journal of Chemical Physics, 118(14):6562-6571
- Country of Publication:
- United States
- Language:
- English
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