Bimetallic Gold/Palladium Catalysts: Correlation between Nanostructure and Synergistic Effects

Abstract

Au nanoparticles are known to be a good catalyst or an effective promoter for a wide range of catalytic reactions. Bimetallic Au-Pd nanoparticles supported on activated carbon were synthesized following a twostep procedure: immobilization of Au sol onto activated carbon followed by immobilization of Pd(0). The catalysts showed superior activities compared to monometallic Pd or Au nanoparticles on the same support. A series of catalysts with Au:Pd ratios varying from 9.5:0.5 to 2:8 were prepared. These catalysts were characterized by TEM, HRTEM, EDX, and X-ray mapping techniques to obtain morphological information, particle size distributions, crystalline structure, and distribution of the two metals. Correlating with the result from catalytic tests of selective oxidation of glycerol to glyceric acid, we found that the surface configuration of Pd monomers isolated by Au atoms has a substantial effect on activity and stability. The Au:Pd ratio on the surface of the particles is the key parameter and can be finely tuned to achieve optimal catalytic performance. The segregation or inhomogeneity of Pd weakens the synergistic effect of the bimetallic catalyst

Understanding the synergistic effects of gold bimetallic catalysts

“…The synergistic effect between the isolated single atom and the host cluster has also been found in other reactions, such as acetoxylation of ethylene to vinyl acetate [116], selective oxidation of glycerol to glyceric acid [117], aerobic oxidation of alcohols [118], and electrocatalytic production of H 2 O 2 [119]. In these reactions, the role of single atoms of impurity is to limit the byproduct formation, thus improving the selectivity toward the desired reaction pathway and the stability against being poisoned by byproducts.…”

Size and alloying induced shift in core and valence bands of Pd-Ag and Pd-Cu nanoparticles

“…In earlier reports, there have been some efforts towards synergizing the useful effects of alloying and size reduction by preparing Pd-alloy nanoparticles. [16][17][18][19][20][21] The electronic properties of Pd-Ag and Pd-Cu alloy nanoparticles have been studied as a function of composition using the chemical synthesis routes. 16,17,20,21 Sequential or co-evaporation of the two components using e-beam, thermal heating, sputtering, and laser ablation has been used to prepare Pd-Cu and Pd-Ag alloy thin films and nanoparticulate layers having large variations in composition or phase impurity.…”

Selective Oxidation of Raw Glycerol Using Supported AuPd Nanoparticles

“…As already highlighted in the literature, these results confirmed the beneficial effect of the presence of heteroatoms on the carbon nanofibers' surface in terms of stabilization of the metal nanoparticles with a better particle size distribution. In the case of AuPd on activated carbon, alloyed AuPd nanoparticles with a uniform composition and homogeneity were obtained [24][25][26]. In the other cases, most of the nanoparticles were alloyed, but the Au/Pd ratio was inhomogeneous from cluster to cluster.…”

“…AuPd catalysts were synthesized by impregnation of preformed metal nanoparticles using polyvinyl alcohol as a protective agent. We reported on a two-step procedure for the preparation of activated carbon-supported AuPd alloy nanoparticles (NPs) [24][25][26]. In this procedure, after immobilization of a preformed gold sol on activated carbon, a sol of palladium was generated in the presence of Au/AC using H2 as the reducing agent.…”