Carbon-supported palladium catalysts. Molecular orbital study

Geometric and electronic structures of palladium clusters supported on activated carbon (Pdn/AC) are analyzed using semiempirical quantum chemical modeling for n=1–22. Qualitative reliability of the results is checked by DFT calculations for n=1–6. Supported Pd atoms and clusters are shown to be strongly bound to unsaturated and defect surface sites. In such positions, interaction of Pd atoms with the support is much stronger than that with each other. That provides the driving force for atomic dispersity of Pd/AC catalysts. Geometry of small clusters is determined by morphology of an adhesion position. Nanosized particles form compact three-dimensional structures with close-packed triangular surfaces. AC support causes notable excitations in the electronic structure of metal atoms directly bound to the support, resulting in the direct nucleation of fcc-like structures. These excitations are quickly extinguishing when moving far from the support surface.