Size, nanostructure, and composition dependence of bimetallic Au–Pd supported on ceria–zirconia mixed oxide catalysts for selective oxidation of benzyl alcohol

Abstract

A bimetallic Au–Pd catalyst supported on ceria–zirconia with Au:Pd molar ratio 0.8 has been synthesized using a simultaneous deposition–precipitation method and oxidized at 250, 450, and 700 °C in order to modify its particle size, nanostructure, and composition. Combined X-ray energy dispersive spectroscopy (XEDS) and X-ray photoelectron spectroscopy (XPS) analysis clearly evidence that the bimetallic Au–Pd catalyst oxidized at 250 °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 ceria–zirconia 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 °C. However, oxidation at 700 °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 ceria–zirconia 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 AuPd@Pd nanostructures on ceria–zirconia supports.