N<sub>2</sub>O Adsorption and Photochemistry on Ceria Surfaces
Chengwu Yang, Yunjun Cao, Philipp N. Pleßow, Jia Wang, Alexei Nefedov, Stefan Heißler, Felix Studt, Yuemin Wang, Hicham Idriss, Thomas G. Mayerhöfer, Christof Wöll
Abstract
Catalytic decomposition of nitrous oxide (N2O) is one of the most promising ways to control N2O emissions, the dominant ozone-depleting substance and the third most potent greenhouse gas. We have investigated the adsorption and photoinduced decomposition of N2O on macroscopic monocrystalline CeO2(111) surfaces by polarization-dependent infrared reflection absorption spectroscopy (IRRAS) in conjunction with core-level (XPS Ce 3d and NEXAFS) and valence band (Ce 4f) spectroscopy as well as DFT+U calculations. The IRRAS results at 110 K show that the νas(NNO) asymmetric stretching vibration of adsorbed N2O exhibits band splitting at relatively low N2O coverage in p-polarized spectra. This band splitting is attributed to polarization-dependent shifts of absorption bands. On reduced ceria (111) surfaces, the desorption energy (0.37 eV) of N2O extracted by IRRAS is found to be higher than on oxidized surfaces. This increasing binding energy is attributed to the attractive coupling with Ce3+ cations formed via surface Ce4+ reduction by by polarons that migrate from the bulk. The photoreaction cross section (with ultraviolet (UV) light = 365 nm at T = 120 K) of the reduced ceria (110) surfaces determined by IRRAS (5 × 10–19 cm2) confirms their much higher activity than that of the reduced CeO2(111).