FTIR study of CO and NOx adsorption and co-adsorption on Cu/silicalite-1

Testing of two different samples of Cu/silicalite-1 with CO reveals the existence of Cu+ sites typical of oxide-supported copper. CO adsorbed on these sites is characterized by a band at 2137 cm(-1). Heating the samples in a CO atmosphere leads to reduction of particular Cu2+ cations and the Cu+ sites formed behave as Cu+ cations exchanged in ZSM-5. Adsorption of CO on these sites results in the formation of dicarbonyls ( ns at 2177 cm(-1) and nas at 2150 cm(-1)) which, after evacuation, are converted into monocarbonyls (v(CO) at 2157 cm(-1)). In the presence of water, mixed Cu+(H2O)(CO) species are formed (v(CO) at 2130 cm(-1)). NO adsorption on Cu/silicalite-1 results in the formation of Cu2+(NO) complexes which are characterized by a broad band centered at 1888 cm(-1). Addition of a small amount of oxygen to the system results in the formation of surface nitrates typical of supported copper catalysts (1630, 1608 and 1578 cm(-1)). In addition, weakly bonded N2O3, N2O4 and NO2 are formed. The reasons for the appearance of Cu+ sites in cationic positions are discussed.