Heat of adsorption of carbon monoxide on a Pt/Rh/CeO2/Al2O2 three-way catalyst using in-situ infrared spectroscopy at high temperatures

The adsorption of CO (1% CO/He mixture) on a 2.9% Pt/0.6% Rh/20% CeO2/Al2O3 (in weight percent) three-way catalyst is studied in the temperature range 300 K-800 K by FTIR spectroscopy using a suitably infrared cell of small volume. The quantitative treatment of the spectra leads to the determination of the evolution of the coverage of the adsorbed species with the temperature. The main adsorbed species is the linear CO form characterized by an IR band at 2063 cm(-1), probably formed on platinum atoms. The heat of adsorption of this species is determined at various coverages in the range 0.36 < theta < 1. In agreement with the literature, a linear relationship is observed between the heats of adsorption and the coverage. The values determined at each coverage (i.e. 116 kJ/mol at theta = 0.8 and 148 kJ/mol at theta = 0.36) are similar to those obtained from calorimetric measurements on platinum-supported catalysts. Similar results are obtained on two platinum-containing solids: 2.9% Pt/Al2O3 and 2.4% Pt/20% CeO2/Al2O3. The procedure described to determine the heat of adsorption of adsorbed CO species at various coverages using FTIR spectroscopy is experimentally easy. However, the disproportionation reaction, 2 CO --> C-ads, + CO2 which may arise at high temperature, limits its application to a specific range of temperatures. (C) 1998 Academic Press.