Carbon-supported palladium catalysts.Molecular orbital study

摘要

Geometric and electronic structures of palladium clusters supported on activated carbon (Pd_n/AC) are analyzed using semiempirical quantum chemical modeling ofr n=1-22.Qualitative reliability of ht results is checked by DFT calculations for n=1-6.Supported Pd atoms and clusters are shown to be strongly bound ot unstaturated and defect surface sites.Insuch positions,interaction of Pd stoms with the support is mucl stronger than that with each other.That provides the driving force for atomic dispersity of Pd/AC catalysts.Geometry of small clusters is detemined 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 structured of metal atoms directly bound to the support,resulting in the direct uncleation of fcc-like structures.These excitations are quickly extinguishing when moving far from the support suface.