The effect of metal deposition order on the synergistic activity of Au-Cu and Au-Ce metal oxide catalysts for CO oxidation

Monometallic Au/Al2O3, MxOy/Al2O3 (M=Cu; Ce) catalysts and bimetallic catalysts with simultaneously (Au + MxOy) and sequentially (MxOy/Au, Au/MxOy) deposited metals were prepared. Oxidation of CO in the presence of these catalysts at 50-450 degrees C was studied. The activity of the catalysts increases in the following series: MxOy/Au/Al2O3 > Au/MxOy/Al2O3 > (Au + MxOy)/Al2O3 > CuxOy/Al2O3 > Au/Al2O3>CexOy/Al2O3. A synergistic effect was detected at 50-250 degrees C: bimetallic catalysts converted up to 50% of CO to CO2, while the monometallic samples were inactive. Increasing the reaction temperature above 250 degrees C results in a decreased synergistic effect, although bimetallic catalysts still possess good activity. The electronic and structural organization of the catalyst active sites before and after the reaction were studied by means of XRD, TEM, EDX, XPS, and DRIFTS techniques. The causes for the synergistic effect and the reaction mechanism in the presence of synergistic catalysts are proposed and discussed. (C) 2014 Elsevier B.V. All rights reserved.