Article,
Carbon monoxide oxidation on the Pt(111) surface: Temperature programmed reaction of coadsorbed atomic oxygen and carbon monoxide
J. Chem. Phys., 78 (2): 963-974 (1983)
DOI: 10.1063/1.444801
Abstract
Carbon dioxide formation from coadsorbed atomic oxygen and molecular
carbon monoxide has been characterized using temperature programmed
reaction spectroscopy over a wide range of initial oxygen and carbon
monoxide coverages. The experiments were performed in an apparatus
containing Auger electron spectroscopy, low energy electron diffraction,
and a multiplexed mass spectrometer for the temperature programmed
reaction experiments. A single reaction limited CO2 peak is observed
in the 320�340 K temperature range over a wide range of initial atomic
oxygen and molecular CO coverages, suggesting that a single reaction
mechanism dominates. The activation energy for CO2 formation ranges
from 166 kJ/mol (40 kcal/mol) for small surface concentrations of
reactive adsorbed atomic oxygen and CO (0.4�1014/cm2) to 68 kJ/mol
(17 kcal/mol) for larger surface concentrations of reactive adsorbed
atomic oxygen and CO (2.5�1014/cm2). Low energy electron diffraction
results indicate that adsorbed atomic oxygen forms islands for surface
concentrations greater than about 0.4�1014 atoms/cm2 (0.10 thetamax)
and suggests that CO forms CO islands when CO is adsorbed on surfaces
containing adsorbed atomic oxygen. The observation that this reaction
does not go to completion during a temperature programmed reaction
cycle indicates that the island structure of the reactants limits
their availability for reaction. Apparently, the reaction proceeds
by diffusion of adsorbed CO to the perimeters of the immobile adsorbed
atomic oxygen islands. Similar effects have been observed previously
during temperature programmed reaction and titration studies of the
hydrogen�oxygen reaction on the Pt (111) surface J. L. Gland, G.
B. Fisher, and E. B. Kollin J. Catal. 77, 263(1982).
