Acetoxylation of ethylene to vinyl acetate (VA) was used to investigate the mechanism of the promotional effect of gold (Au) in a palladium (Pd)-Au alloy catalyst. The enhanced rates of VA formation for low Pd coverages relative to high Pd coverages on Au single-crystal surfaces demonstrate that the critical reaction site for VA synthesis consists of two noncontiguous, suitably spaced, Pd monomers. The role of Au is to isolate single Pd sites that facilitate the coupling of critical surface species to product, while inhibiting the formation of undesirable reaction by-products.

https://science.sciencemag.org/content/sci/310/5746/291.full.pdf

The Promotional Effect of Gold in Catalysis by Palladium-Gold

Metal-mediated reductive hydrodehalogenation of organic halides.

Polyaniline nanostructures and the role of aniline oligomers in their formation

Selective oxidation of primary carbon-hydrogen bonds with oxygen is of crucial importance for the sustainable exploitation of available feedstocks. To date, heterogeneous catalysts have either shown low activity and/or selectivity or have required activated oxygen donors. We report here that supported gold-palladium (Au-Pd) nanoparticles on carbon or TiO2 are active for the oxidation of the primary carbon-hydrogen bonds in toluene and related molecules, giving high selectivities to benzyl benzoate under mild solvent-free conditions. Differences between the catalytic activity of the Au-Pd nanoparticles on carbon and TiO2 supports are rationalized in terms of the particle/support wetting behavior and the availability of exposed corner/edge sites.

https://science.sciencemag.org/content/sci/331/6014/195.full.pdf

Solvent-Free Oxidation of Primary Carbon-Hydrogen Bonds in Toluene Using Au-Pd Alloy Nanoparticles

the National Natural Science Foundation of China (21073208);the Chinese Academy of Sciences

Nano-Gold Catalysis in Fine Chemical Synthesis

Universal mathematical relations between the mean relative size of metallic crystallites (drel(VS)) and their dispersion (FE) in supported metal catalysts have been developed. The relations are:  drel(VS) = 5.01/FE for FE 0.2 the commonly used definition of dVS should be modified. The developed relations apply well to various thermodynamically probable crystallite shapes including fcc cubooctahedra of varying geometry, icosahedra, surface-reconstructed cubooctahedra, bcc rhombic dodecahedra, and hcp truncated bipyramids. The new relations are more precise than the commonly used equation dVS = a/FE, where a is a constant specific to a given metal.

Relation between Crystallite Size and Dispersion on Supported Metal Catalysts

Pd–Au/Sibunit Carbon Catalysts: Characterization and Catalytic Activity in Hydrodechlorination of Dichlorodifluoromethane (CFC-12)

Characterization of Pd–Au/SiO2 Catalysts by X-ray Diffraction, Temperature-Programmed Hydride Decomposition, and Catalytic Probes

Two series of well-mixed Pd–Au/SiO2 catalysts prepared by direct redox method were tested in the reaction of CCl2F2 (CFC-12) hydrodechlorination A moderate selectivity for CH2F2 exhibited by monometallic Pd/SiO2 (∼40%) is significantly increased, up to ∼95%, with Au addition Proper Pd–Au alloying is essential to obtain such a selectivity enhancement Poorly mixed Pd–Au/SiO2 catalysts show the catalytic behaviour not very much different from that of Pd/SiO2, producing a lot of methane Changes in the apparent activation energy are also associated with the degree of Pd–Au alloying After reaction, the Pd/SiO2 and Pd–Au/SiO2 catalysts contain dissolved carbon Hydrogen treatment of carbonized Pd–Au/SiO2 catalysts removes this carbon XRD study of the regenerated samples shows no change in the structure and composition of Pd–Au phase, compared to freshly prereduced bimetallic catalysts

Hydrodechlorination of CCl2F2 (CFC-12) over silica-supported palladium–gold catalysts

A series of carbon-supported palladium-gold (Pd-Au) catalysts prepared by direct redox reaction method and characterized by various techniques were investigated in the reaction of dichlorodifluoromethane (CFC-12) with dihydrogen. The selectivity towards difluoromethane (desired reaction product) was increased upon introducing gold to palladium, from ∼72 to ∼86%, at 180°C. Such a selectivity enhancement was not observed in our previous studies when Pd-Au/C catalysts prepared by incipient wetness impregnation showed inadequate extent of Pd-Au alloying. Conditions of preparation of Pd-Au/C catalysts by the direct redox reaction method are found to affect the amount of deposited metals and the degree of Pd-Au mixing. The latter factor is essential in determining hydrodehalogenation behavior of the catalysts.

Magdalena Bonarowska

Papers

Relation between Crystallite Size and Dispersion on Supported Metal Catalysts

Pd–Au/Sibunit Carbon Catalysts: Characterization and Catalytic Activity in Hydrodechlorination of Dichlorodifluoromethane (CFC-12)

Characterization of Pd–Au/SiO2 Catalysts by X-ray Diffraction, Temperature-Programmed Hydride Decomposition, and Catalytic Probes

Hydrodechlorination of CCl2F2 (CFC-12) over silica-supported palladium–gold catalysts

Hydrodechlorination of CCl2F2 (CFC-12) over Pd-Au/C catalysts