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Nitric Oxide Reaction Pathways on Rutile TiO₂(110): The Influence of Surface Defects and Reconstructions C
- Cao, Yunjun, Yu, Min, Qi, Shandong, Ren, Zhengfeng, Yan, Shishen, Hu, Shujun, Xu, Mingchun
- Journal of physical chemistry 2018 v.122 no.41 pp. 23441-23450
- adsorption, catalytic activity, chemical bonding, nitric oxide, nitrogen, nitrous oxide, oxidation, oxygen, spectroscopy, titanium dioxide
- TiO₂ exhibits excellent catalytic performance in degrading NO to N₂O or N₂. However, up to now, the detailed reaction pathways of NO on TiO₂ surfaces are still debatable. In this paper, we studied NO adsorption and reactions on differently treated rutile TiO₂(110) surfaces by using polarization/azimuth-resolved infrared reflection absorption spectroscopy (IRRAS). It is found that the surface defects [the oxygen vacancies (Vo)] and reconstructions on TiO₂(110) have a strong effect on the reaction pathways of NO → N₂O conversion. The simplest pathway occurs on the defect-free oxidized TiO₂(110) surface in which two NO molecules adsorbed on adjacent surface Ti (Ti₅c) sites first couple to the cis-(NO)₂/Ti&Ti dimer though a N–N bond, and then convert to N₂O species. On the moderately reduced TiO₂(110)-(1 × 1) surface, due to the presence of surface Vo and the resulting polaron, two NO molecules adsorbed, respectively, on Vo sites and adjacent Ti₅c sites couple to the trans-(NO)₂/Ti&Vo dimer, and then convert to N₂O before the cis-(NO)₂/Ti&Ti dimers occur. On the highly reduced quasi-TiO₂(110)-(1 × 2) surface, however, the Ti₂O₃ row fragments hamper the conversion of trans-(NO)₂/Ti&Vo → N₂O, and thus hamper the subsequent cis-(NO)₂/Ti&Ti formation without polaron. In this case, the conversion of both the trans-(NO)₂/Ti&Vo dimer and the isolated NO monomer to N₂O is likely to be triggered by the gas NO impingement. The structure–reactivity relationship we proposed is helpful in understanding the catalytic mechanism of NO degradation on TiO₂ surfaces.