LAUSR

Reduced Au-Cu/CeO 2 catalysts (Cu/Au = 1, 3) are more efficient towards the preferential oxidation of CO (PROX) than their calcined counterparts. They exhibit lower activation energies and CO partial reaction orders (a CO), and even more interestingly, significantly higher O 2 partial reaction orders (b O2). For the sto-ichiometric composition in particular (Au 1 Cu 1 /CeO 2-R), the partial pressure of oxygen has a higher impact on the reaction rate than the partial pressure of CO (b O2 > a CO), which is unprecedented in low temperature catalysis involving gold and a reducible oxide support. DRIFTS studies further show (1) that Au 1 Cu 1 /CeO 2-R contains electron-deficient, alloyed Cu atoms (Au-Cu +) and (2) that the formation of CO 2 is enhanced by the preadsorption of O 2 rather than the preadsorption of CO. This suggests that CO oxidation proceeds via a Langmuir-Hinshelwood-type, bifunctional mechanism, involving CO adsorbed on Au 0 sites and oxygen adsorbed on electron-deficient, gold-alloyed copper sites. This alloy-mediated oxygen activation could be the key to the superior PROX activity of Au 1 Cu 1 /CeO 2-R.