Pd-Au bimetallic catalysts: understanding alloy effects from planar models and (supported) nanoparticles.
Pd-Au bimetallic catalysts often display enhanced catalytic activities and selectivities compared with Pd-alone catalysts. This enhancement is often caused by two alloy effects, i.e., ensemble and ligand effects. The ensemble effect is dilution of surface Pd by Au. With increasing surface Au coverages, contiguous Pd ensembles disappear and isolated Pd ensembles form. For certain reactions, for example vinyl acetate synthesis, this effect is responsible for reaction rate enhancement via the formation of highly active surface sites, e.g., isolated Pd pairs. The disappearance of contiguous Pd ensembles also switches off side reactions catalyzed by these sites. This explains selectivity increase of certain reactions, for example direct H2O2 synthesis. The ligand effect is electronic perturbation of Au to Pd. By direct charge transfer or affecting bond length, the ligand effect causes the Pd d band to be more filled and the d-band center away from the Fermi level. Both changes make Pd more "atomic like" therefore binding reactants and products weaker. For certain reactions, this eliminates the so-called "self poisoning" and enhances activity/selectivity.
- Research Organization:
- Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC05-76RL01830
- OSTI ID:
- 1056150
- Report Number(s):
- PNNL-SA-87514; KC0302010
- Journal Information:
- Chemical Society Reviews, 41(24):8009-8020, Journal Name: Chemical Society Reviews, 41(24):8009-8020
- Country of Publication:
- United States
- Language:
- English
Similar Records
New Role of Pd Hydride as a Sensor of Surface Pd Distributions in Pd-Au Catalysts
Synthesis and Characterization of Pd-based Nanomaterials