The CO oxidation with on an active catalyst has been studied using a TAP (temporal analysis O 2 Au/Ti(OH) 4 * of products) transient technique to gain insights into the CO oxidation mechanism. Taking advantage of the TAP system, we have tried to elucidate the controversial mechanism proposed for the CO oxidation on supported gold catalysts. PumpÈprobe experiments have been performed to determine the lifetime of surface reactive intermediates involved in the oxidation reaction. In a typical pumpÈprobe experiment the catalyst is Ðrst charged with a reactant pulse from the pump valve and then interrogated with a di †erent pulse from the probe valve. Varying the time between the pump and probe pulses gives information related to the lifetime of surface intermediates. The pumpÈprobe experiments together with single-pulse experiments revealed that molecularly and irreversibly adsorbed oxygen contributed to the catalytic CO oxidation. When CO was a pump molecule, the yield was not inÑuenced by the pumpÈprobe time interval. This means that CO CO 2 reversibly adsorbs on the surface with a lifetime long enough to react with oxygen. Moreover, the nature and role of oxygen species in the reaction have been examined in the TAP reactor using transient 18O 2 experiments. The results revealed that oxygen passed over the catalyst without isotope scrambling and that the lattice oxygen atoms exchanged only with formed by the CO oxidation reaction. CO 2

The adsorption kinetics on Au/Ti(OH)4* (a newly developed Au catalyst, active for low-temperature CO oxidation) for CO, O2, and CO2 in the temperature range 298–473 K was determined by temporal analysis of products (TAP) technique. The response signals from the single-pulse TAP experiments were analyzed using a statistical approach, and they were fitted to analytical models in order to establish the adsorption/desorption parameters. The pulse response of a non-adsorbing gas (argon) was used as a “reference”. The experiments revealed that: CO molecules reversibly adsorbed on the catalyst surface; O2 molecularly adsorbed , irreversibly for high pulse intensities and reversibly for low pulse ones; CO2 molecules irreversibly adsorbed on the surface, probably as carbonates. This catalyst exhibited an apparent negative activation energy for irreversible adsorption of O2.