The direct catalytic decomposition of NO on Rh/Al2O3, Rh/C, Pd/Al2O3, and Pd/C catalysts was investigated at 673 K by in situ infrared (IR) coupled with mass spectroscopy (MS). NO decomposition on these catalysts initially produced N-2 and adsorbed oxygen. Different catalysts exhibit different capabilities for manipulating adsorbed oxygen. Rh/Al2O3 shows little activity for oxygen desorption, resulting in loss of catalyst activity; Rh/C shows the ability for promoting the adsorbed oxygen-carbon reaction, removing oxygen in the form of CO2; Pd/Al2O3 shows some activity for O-2 desorption. Use of carbon as a support for Pd promotes O-2 desorption, resulting in improvement of NO decomposition activity. The in situ IR results provide evidence to support the behavior of adsorbed oxygen on carbon-supported Rh and Pd catalysts. (C)2000 Elsevier Science B.V. All rights reserved.