IR studies of coadsorption of CO and NO on Co2+ and Cu+ sites in zeolites

The present study was carried out to follow the effect of CO coadsorption on the properties of NO adsorbed on the same Co2+ sites. As the activation of the different molecules was found to be specially pronounced for Cu+ in MFI and FAU zeolites, the coadsorption of CO and NO on Cu+ sites was also examined. Our previous studies reveled that the presence of the electron donor ammonia and pyridine molecules strongly weakened the multiple bond in NO molecule bonded to the same Cu+ cation. The present IR experiments evidenced that CO acted as an electron acceptor. The flow of an electron density from the antibonding π* orbital of NO via Co2+ or Cu+ to the antibonding π* orbital of CO results in strengthening of the NO bond and in weakening of the CO bond.