Use of overtones and combination modes for the identification of surface NOx anionic species by IR spectroscopy

Adsorption of NO on ZrO2 produces a series of compounds, among them N2O whi ch is characterized by a band at 1232 cm(-1) and the respective overtone (1 2 times less intense) at 2466 cm(-1). Co-adsorption of NO and O-2 results i n the formation of different surface nitrates. Bridging nitrates are charac terized by a set of bands at 1640, 1220 and 1004 cm(-1) and manifest a comb ination mode at 2612 cm(-1). Bidentate nitrates (1588-1568, 1240 and 1042 c m(-1)) show a combination mode at 2580 cm(-1), which for monodentate nitrat es (1515, 1295 and 1019 cm(-1)) is found at 2522 cm(-1). In all these cases the combination mode is by about two orders of magnitude less intense than the fundamental band in the 1650-1500 cm(-1) region. The use of overtones and combination modes is proposed to help the assignments of the NOx bands. It is demonstrated that bands in the 1650-1550 cm(-1) region, produced aft er NO + O-2 co-adsorption on Fe-ZSM-5, are due to nitrate species.