The kinetics of CO oxidation over an alumina supported Cu catalyst are
examined using successive oxidation and reduction cycles. Experiments
were done at a temperature of 493 K with isotopically labelled gases
in a tubular reactor. Surface species were monitored during transients
in an FTIR flow cell. For the reoxidation of the catalyst a three-ste
p mechanistic model is proposed. The kinetic constants are determined
by mathematical modelling. The role of carbonates is found to be minor
in the production of CO2 in contrast to carbonyls which are shown to
be the intermediates. A net dissociation of the CO bond was observed d
uring reduction caused by adsorption of CO2 on a partly reduced cataly
st under formation of carboxylates and its subsequent decomposition to
CO,2 thereby leaving oxygen on the catalyst. A complete mechanistic s
cheme is presented which allows us to describe qualitatively and in pa
rt quantitatively the experimental results. This study shows that the
use of forced oscillations is a powerful tool with strong elucidating
abilities in mechanistic investigations in heterogeneous catalysis.