The problem of the desorption of oxygen from transition metal ion base-exchanged zeolites during NO decomposition is considered. The TPD patterns of fully oxidized CuZSM-5-14-114 and CuY-2.5-75 were determined. Both contained nearly identical peaks from (\mathrm{O}{2}) that desorbed at (T<450 \mathrm{~K}) and at (T>773 \mathrm{~K}), but the former zeolite also had two peaks that appeared in the range (572 \mathrm{~K}<T<723 \mathrm{~K}) which have been associated with that formed during the NO decomposition reaction. The TPD data could be related to binding energies obtained from van't Hoff plots of dissociation pressures from preparations preevacuated at several different temperatures. The lowtemperature form is probably a molecular chemisorption, while those with substantial binding energies desorbing at higher temperatures are atomically bound extralattice oxygens. The exchange of ({ }^{1 \times} \mathrm{O}{2}) with the ({ }^{16} \mathrm{O}) of the catalyst was studied, as well as the products formed from the decomposition of ({ }^{16} \mathrm{~N}^{18} \mathrm{O}) into the elements. The results from these experiments defined an important role for the lattice oxygen in the atom recombination and desorption of (\mathrm{O}_{2}) from the catalyst. 1993 Academic Press. Inc.