TAP study on CO oxidation on a highly active Au/Ti (OH)(4)(*) catalyst

The CO oxidation with O-2 on an active Au/Ti(OH)(4)* catalyst has been stud ied using a TAP (temporal analysis of products) transient technique to gain insights into the CO oxidation mechanism. Taking advantage of the TAP syst em, we have tried to elucidate the controversial mechanism proposed for the CO oxidation on supported gold catalysts. Pump-probe experiments have been performed to determine the lifetime of surface reactive intermediates invo lved in the oxidation reaction. In a typical pump-probe experiment the cata lyst is first charged with a reactant pulse from the pump valve and then in terrogated with a different pulse from the probe valve. Varying the time be tween the pump and probe pulses gives information related to the lifetime o f surface intermediates. The pump-probe experiments together with single-pu lse experiments revealed that molecularly and irreversibly adsorbed oxygen contributed to the catalytic CO oxidation. When CO was a pump molecule, the CO2 yield was not influenced by the pump-probe time interval. This means t hat CO reversibly adsorbs on the surface with a lifetime long enough to rea ct with oxygen. Moreover, the nature and role of oxygen species in the reac tion have been examined in the TAP reactor using O-18(2) transient experime nts. The results revealed that oxygen passed over the catalyst without isot ope scrambling and that the lattice oxygen atoms exchanged only with CO2 fo rmed by the CO oxidation reaction.