A molecular beam study of the catalytic oxidation of CO on a Pt(111) surface

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*LH =24.1 kcal/mole and a pre-exponential υ4 =0.11 cm2 particles−1 sec−1. At very high oxygen coverage, E*LH decreases to about 11.7 kcal/mole and υ4 to about 2×10−6 cm2 particles−1 sec−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 CO2 below 540 K. The CO2 product angular distribution varies from cosγ to cos4γ depending sensitively upon the adsorbed reactant concentrations.

Monte Carlo simulations of a simple model for the electrocatalytic CO oxidation on platinum

“…9,10 This situation is in contrast with the CO oxidation on the Pt/gas interface, for which CO mobility is known to be high. 37 Our MC results do not directly lend support to the idea that CO mobility is low at the platinum/solution interface. The experimental voltammetric peak on Pt͑100͒ and Pt͑111͒ is very sharp, which can only be reproduced by our simulations if CO diffusion is fast.…”

Reversible structural transformation of FeOx nanostructures on Pt under cycling redox conditions and its effect on oxidation catalysis

“…2c). Considering that CO oxidation on Pt(111) would be hindered by strongly adsorbed CO species at modest temperatures, 41 the facile removal of surface adsorbed CO by O 2 occurring on the FeO 1Àx /Pt(111) surface at RT confirms the promotional effect of FeO 1Àx nanoislands on CO oxidation. 16,17 In contrast, the c(4 Â 2)-CO pattern formed on the FeO 2Àx /Pt(111) surface remains unchanged after purging the surface with the same amount of O 2 ( Fig.…”

CO 2 desorption dynamics on specified sites and surface phase transitions of Pt(110) in steady-state CO oxidation

“…CO͑a͒ has a longer surface-residence time on oxygencovered surfaces until its removal as CO 2 compared with its lifetime on one adsorption site 23 and can quickly and widely move over oxygen-covered areas at elevated temperatures. In fact, it has been satisfactorily confirmed theoretically 24 and experimentally 4 that CO is oxidized on sites for oxygen adsorption.…”

“…Usually, observation of this high potential is obscured in the overall reaction rate measurements because the CO 2 formation process has never been the rate-determining step under steadystate CO oxidation conditions on platinum metals. 1,23 In fact, the rate-determining step is either CO adsorption or O 2 dissociation.…”