Catalytic Consequences of Reactive Intermediates during CO Oxidation on Ag Clusters

Abstract

Kinetic measurements, microkinetic modeling, and CO and O2 uptake experiments lead to a proposed mechanism for CO oxidation on dispersed Ag cluster surfaces. CO turnovers occur via kinetically relevant reactions between O2* and CO* on Ag cluster surfaces nearly saturated with O* and CO*. The operating pressure ratio of O2 to the square of CO, [O2]-to-[CO]2, dictates the relative O* and CO* coverages and in turn the rate coefficients. Low [O2]-to-[CO]2 ratios lead to Ag cluster surfaces saturated with CO*, during which the first-order rate coefficients (rCO[CO]−1) increase linearly with the pressure ratio. As the [O2]-to-[CO]2 ratio increases, the CO* coverages decrease and O* coverages concomitantly increase, and the rate coefficients become independent of the [O2]-to-[CO]2 ratio. CO* binds to Ag clusters more strongly than O*, and as a result, CO* coverages decrease and O* coverages increase as the reaction temperature rises when comparing at a constant [O2]-to-[CO]2 ratio. The rate coefficients for CO o...