COMBINED INFRARED AND MASS-SPECTROMETRIC STUDY OF REACTIONS OF ADSORBED NO AND CO ON 0.5 WT-PERCENT RB SIO2 CATALYST/

NO adsorption, CO adsorption, NO temperature-pro rammed desorption and decomposition (TPD), and temperature-programmed reaction (TPR) of NO- CO have been studied over 0.5 wt% Rh/SiO2 catalysts by a combined infr ared and mass spectrometric technique. Infrared study reveals that the high wavenumber Rh-NOdelta- at 1723-1740 cm(-1) is the dominant adsor bate during TPD and TPR with NO:CO = 1:1. During TPR, CO reduces part of Rh surface resulting in the formation of the low wavenumber Rh-NOde lta- at 1634-1680 cm(-1). Increasing CO partial pressure (i) promotes the formation of Rh-0 sites, producing linear CO, (ii) increases the s electivity to N2O below the light-off temperature, (iii) raises the li ght-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/SiO2 shows that different dispersion of Rh crysta llites on SiO2 support results in significant variation in chemisorpti ve and reactive properties of Rh metal for the NO-CO reaction.