The direct catalytic decomposition of NO on Rh/Al 2 O 3 , Rh/C, Pd/Al 2 O 3 , and Pd/C catalysts was investigated at 673K 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/Al 2 O 3 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 CO 2 ; Pd/Al 2 O 3 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.