  A bimetallic Au-Pd catalyst supported on ceriazirconia with Au:Pd molar ratio
0.8 has been synthesized using a simultaneous deposition-precipitation method
and oxidized at 250, 450, and 700 $^\circ$C in order to modify its particle
size, nanostructure, and composition. Combined Xray energy dispersive
spectroscopy and Xray photoelectron spectroscopy analysis clearly evidence that
the bimetallic Au-Pd catalyst oxidized at 250 $^\circ$C is made up of a mixture
of monometallic Au and Pd and bimetallic Au-Pd nanoparticles with Au:Pd ratios
varying over a wide range. Increasing oxidation temperature leads to a stronger
interaction between Au and Pd. Meanwhile, a slight increase of particle size
and a narrowing of the Au:Pd ratio in the bimetallic nanoparticles take place.
Compared with titania and activated carbon supports, the resistance against
sintering at high temperatures of Au-Pd metal particles supported on
ceriazirconia is proven to be higher. A synergistic effect has been observed
for selective oxidation of benzyl alcohol on these catalysts. The catalytic
activity decreases only slightly after oxidation at 450 $^\circ$C. However,
oxidation at 700 $^\circ$C results in much lower catalytic activity. Migration
of Pd onto Au particles during oxidation of benzyl alcohol enhances the
catalytic activity of a physical mixture of monometallic Au and Pd supported on
ceriazirconia catalysts. This fact, jointly with an analysis of the intrinsic
activity, reveals the influence of the actual nature of Au-Pd interactions in
the bimetallic particles, which points to higher activity of Au@Pd or Au@Pd@Pd
nanostructures on ceria-zirconia support.
