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Catalytic Decomposition o NODuring the first semi-annual period of the project, NO adsorption, CO adsorption, NO temperature-programmed desorption and decomposition (TPD), and temperature-programmed reaction (TPR) of NO-CO have been studied over 0.5 wt% Rh/SiOz catalysts by a combined infrared and mass spectrometric technique. Infrared study reveals that the high wavenumber Rh-NOS-at 1723-1740 cm-1 is the dominant adsorbate during TPD and TPR with N0:CO = 1:l.During TPR, CO reduces part of Rh surface resulting in the formation of the low wavenumber Rh-NOS-at 1634-1680 cm-l. Increasing CO partial pressure (i) promotes the formation of Rh to Rho sites, producing hear CO, (ii) increases the selectivity to N20 below the light-off temperature, (%) raises the light-off temperature, and (iv) promotes the formation of Si-NCO and Rh-NCO.Comparison of results of the present study with those of previous studies on 4 wt% Rh/SiO2shows that different dispersion of Rh crystallites on Si02 support results in significant variation in chemisorptive and reactive properties of Rh metal for NO-CO reaction.