Adsorption of NO and NO2 on cobalt exchanged type-A (Co-A) zeolite, has been studied by combining experimental and theoretical techniques. Adsorption energies were determined from temperature programmed desorption (TPD) measurements and ab initio calculations at the B3LYP/6-31G(d) level of theory. TPD profiles suggest that NO is disproportionated upon desorption on Co-A while NO2 desorbs without transformation. An eight-atom cluster model of the transition metal and its closest environment in zeolite Co-A appears to qualitatively reproduce basic features of NOx adsorption. Results from geometrical optimizations confirm that nitrogen monoxide (NO) is preferentially adsorbed through its nitrogen atom, whereas the two oxygen atoms of nitrogen dioxide (NO2) appear to interact more favorably with Co-A. Upon NO adsorption on Co-A, a bent cobalt-mononitrosyl complex is formed. However, a negative charge is not developed on the nitrosyl and cobalt is not oxidized. Similarly, adsorption of nitrogen dioxide over Co-A does not change the oxidation state of cobalt. Theoretical calculations appear to reproduce the experimental adsorption energies within expected limits of error. (C) 2003 Elsevier B.V. All rights reserved.