Carbon Monoxide Oxidation Over a Pt/A12O3 Catalyst: Temperature Programmed Studies Over an Extended Coverage Range
D J. Burnett, Daniel A. Fischer, J L. Gland
Temperature programmed reaction spectroscopy (TPRS) experiments were performed on a 4.8 wt % Pt/Al2O3 catalyst to characterize carbon monoxide oxidation. CO and oxygen desorption experiments were performed to characterize the platinum surface in these supported catalysts. These chemisorption studies suggest two dominant surface sites (1) terrace sites with similar chemical behavior to the Pt(111) surface and (2) defect platinum sites which have properties similar to platinum steps and kinks. Desorption results are not influenced substantially by diffusion limitations. If the catalyst surface is annealed to remove less tightly bound CO, desorption begins at the annealing temperature indicating the forms of CO are discrete. These partial desorption experiments indicate that diffusion is not rate limiting during either adsorption or desorption. TPRS studies of coadsorbed oxygen and CO reveal a complex series of oxidation peaks. Three major carbon dioxide reaction channels were detected. First, at 350 K, carbon dioxide is formed due to the reaction between intimately mixed CO and atomic oxygen adsorbed on terrace platinum sites. The second oxidation channel occurs at 500 K. This reaction is ascribed to the surface diffusion limited reaction between coadsorbed CO and atomic oxygen on terrace sites where intimate surface mixing does not occur. The third and final oxidation channel occurs at 680 K and is attributed to the reaction between coadsorbed atomic oxygen and CO adsorbed at defect sites. For all coverages and stoichiometries studied, some of the CO and oxygen desorb without reacting, indicating CO surface diffusion rates are slower than CO desorption rates. Experiments over a wide range of CO and oxygen coverages suggest repulsive interactions and island formation when CO and oxygen are coadsorbed. Even on these small platinum particles, oxygen preferentially adsorbs away from preadsorbed carbon monoxide.
, Fischer, D.
and Gland, J.
Carbon Monoxide Oxidation Over a Pt/A1<sub>2</sub>O<sub>3</sub> Catalyst: Temperature Programmed Studies Over an Extended Coverage Range, Surface Science
(Accessed December 2, 2023)