IR spectroscopy study of CO and NOx adsorption on a Cu/Zr-HMS catalyst

The adsorption of CO, NO and NO, and the co-adsorption of CO + NO and NO + O-2 on Cu/Zr-HMS have been investigated by infrared spectroscopy. Carbon monoxide and nitrogen monoxide are adsorbed selectively on Cu+ and Cu2+ cations, respectively. Owing to back pi-donation, the Cu+-CO complexes [nu(CO) at 2132 cm(-1)] are relatively stable towards evacuation and water vapor treatment. On the contrary, the Cu2+-NO nitrosyls [nu(NO) at 1888 cm(-1)] are easily decomposed during evacuation. Adsorption of NO2 and co-adsorption of NO and O-2 cause the formation of weakly adsorbed N2O4 (a band at 1740-1730 cm(-1)) and N2O3 (bands at 1904 and 1540 cm(-1)) as well as strongly bound nitrates (bands at 1620-1550 cm(-1)). The latter possess a high oxidation ability, oxidizing NO at room temperature and methane at 200 degrees C. The results obtained show that the coordination state of copper ions in Cu/Zr-HMS is closer to their state in Cu/SiO2 and Cu/Al2O3 than to that in Cu-ZSM-5, which is due to the absence of strongly acidic OH groups in Zr-HMS. (C) 1999 Elsevier Science B.V. All rights reserved.