Combined infrared and mass spectrometric study of reactions of adsorbed NO and CO on 0.5 wt% Rh/SiO 2 catalyst

Abstract

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/SiO 2 catalysts by a combined infrared and mass spectrometric technique. Infrared study reveals that the high wavenumber RhNO δ− at 1723–1740 cm −1 is the dominant adsorbate 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-NO δ−1 at 1634–1680 cm −. Increasing CO partial pressure (i) promotes the formation of Rh 0 sites, producing linear CO, (ii) increases the selectivity to N 2O below the light-off temperature, (iii) 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/SiO 2 shows that different dispersion of Rh crystallites on SiO 2 support results in significant variation in chemisorptive and reactive properties of Rh metal for the NOCO reaction.