Article,
A molecular-beam study of the cataytic-oxidation of CO on a Pt(111) surface
J. Chem. Phys., 73 (11): 5862--5873 (1980)
DOI: 10.1063/1.440029
Abstract
The oxidation of carbon monoxide catalyzed by Pt(111) was studied
in ultrahigh vacuum using reactive molecular beam--surface scattering.
Under all conditions studied, the reaction follows a Langmuir--Hinshelwood
mechanism: the combination of a chemisorbed CO molecule and an oxygen
adatom. When both reactants are at low coverage, the reaction proceeds
with an activation energy E(/sub LH/ =24.1 kcal/mole and a pre-exponential
upsilon/sub 4/ =0.11 cm/sup 2/ particles/sup -1/ sec/sup -1/. At
very high oxygen coverage, E(/sub LH/ decreases to about 11.7 kcal/mole
and upsilon/sub 4/ to about 2 x 10/sup -6/ cm/sup 2/ particles/sup
-1/ sec/sup -1/. This is largely attributed to the corresponding
increase in the energy of the adsorbed reactants. When a CO molecule
incident from the gas phase strikes the surface presaturated with
oxygen, it enters a weakly held precursor state to chemisorption.
Desorption from this state causes a decrease in chemisorption probability
with temperature. Once chemisorbed, the CO molecule then has almost
unit probability of reacting to produce CO/sub 2/ below 540 K. The
CO/sub 2/ product angular distribution varies from cos..gamma.. to
cos/sup 4/..gamma.. depending sensitively upon the adsorbed reactant
concentrations.
Tags
- and
- beams;
- carbon
- catalysis;
- chalcogenides;
- chemical
- classical
- collisions;
- compounds;
- elements
- elements;
- general
- mechanics,
- metals;
- molecular
- molecule
- monoxide;
- oxidation;
- oxides;
- oxygen
- physics;
- platinum
- platinum;
- quantum
- reactions;
- surfaces;
- transition
