| Abstract
| - The adsorption of CO (1% CO/He mixture, 1 atm total pressure) in the presence of several gases isstudied on a reduced 2.9% Pt/Al2O3 catalyst in the 300−740 K temperature range by using Fourier transforminfrared spectroscopy. A strong IR band is observed at 2075 cm-1 in the absence of a second gas associatedto a weak and broad IR band around 1850 cm-1 ascribed to linear and multibound CO species, respectively.We have previously shown (a) that the evolution of the intensity of the IR band of the L species with theadsorption temperature Ta leads to the determination of the change in the coverage θ of this adsorbed COspecies with Ta and (b) that the curve θ = f(Ta) allows the determination of the heats of adsorption of theL species at several coverages (denoted by ELθ) using an adsorption model. In the present study, themodifications of the IR band of the L species in the presence of a second gas (H2 (1% CO/H2), O2 (1% CO/x%O2/He with x < 0.25), CO2 (1% CO/14% CO2/He), H2O (1% CO/y% H2O/He with y = 0.5 and 3.5), and C2H4(1% CO/2% C2H4/10% H2/He)) are studied in the temperature range 300−740 K. It is shown that thecoverage of the L species is not significantly modified for Ta> 450 K by the presence of the coadsorbedspecies even when catalytic reactions are detected. One may conclude (a) that the heat of adsorption ofthe L species is not significantly modified in the presence of coadsorbed species and (b) that the coverageof the L species during several catalytic reactions on Pt/Al2O3 (CO/H2, CO/H2O, CO/O2 with a CO/O2 ratio> 2) is not significantly different from the coverage determined at the adsorption equilibrium. However,this last conclusion is not true for CO/O2 ratios of <2.
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