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

Abstract

Abstract The adsorption of CO, NO and NO 2 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 Cu 2+ cations, respectively. Owing to back π -donation, the Cu + –CO complexes [ ν (CO) at 2132 cm −1 ] are relatively stable towards evacuation and water vapor treatment. On the contrary, the Cu2 + –NO nitrosyls [ ν (NO) at 1888 cm −1 ] are easily decomposed during evacuation. Adsorption of NO 2 and co-adsorption of NO and O 2 cause the formation of weakly adsorbed N 2 O 4 (a band at 1740–1730 cm −1 ) and N 2 O 3 (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°C. The results obtained show that the coordination state of copper ions in Cu/Zr-HMS is closer to their state in Cu/SiO 2 and Cu/Al 2 O 3 than to that in Cu-ZSM-5, which is due to the absence of strongly acidic OH groups in Zr-HMS.