Journal of Catalysis, Vol.394, 245-258, 2021
Infrared spectra of surface nitrates: Revision of the current opinions based on the case study of ceria
Nitrates formed on ceria surface were investigated by FTIR spectroscopy and DFT methods. Isotope labelling (N-15, O-18) was utilized to strengthen the conclusions. We found that the structures usually associated with monodentate nitrates (IR bands at ca. 1460, 1300 and 1030 cm(-1)), although bound to surface most strongly via one oxygen atom, are tridentate nitrates with C-2v symmetry. The bidentate nitrates, as a rule, simultaneously bridge and chelate cerium cations. The spectral difference between these species is due to the binding geometry and symmetry reduction. An experimental approach is proposed to distinguish between different nitrate coordination. It is based on the split of the higher frequency IR band (1650-1450 cm(-1)) upon partial exchange with O-18: one new band appears for bidentate nitrates and two new bands for monodentate and the observed tridentate nitrates. (c) 2020 Elsevier Inc. All rights reserved.