Species formed during NO adsorption and NO + O-2 co-adsorption on ceria: A combined FTIR and DFT study

Adsorption of NO and co-adsorption of NO and O-2 on ceria have been re-investigated by FTIR spectroscopy. To provide unambiguous assignments of the IR bands, adsorption of (NO)-N-15 and co-adsorption of (NO)-N-14 +(NO)-N-15 isotopic mixtures have also been studied and DFT calculations performed. At the initial adsorption stages mainly symmetric nitrite species (2472, 1304, ca. 1160 and 822 cm(-1)) and transhyponitrites ([N2O2](2-), ca. 1100 cm(-1)) are simultaneously produced as a result of NO disproportionation. At further stages non-symmetric NO2- species (1393 and 1014cm(-1)), N2O (2240, 1252 cm(-1)) and small amount of nitrates are formed. Nitrates are the only surface products of the thermal decomposition of the nitrites and hyponitrites. In the presence of small amounts of oxygen, the hyponitrites are very easily oxidized. In contrast, all nitrites increase in concentration after addition of small amount of O-2 to the NO/CeO2 system but are gradually oxidized in the presence of higher amount of oxygen giving rise to different surface nitrates. (C) 2018 Elsevier B.V. All rights reserved.