In the course of this study, a series of mononuclear palladium phosphine complexes, trans-[PdX2(PMe3)2] and the binuclear analogues, trans- [Pd2X4(PR3)2] (X = C1, Br or I; R=Me, Et, Pri or Bu), were prepared. The purity of the complexes were confirmed using 1H and 31P NMR spectroscopy and microanalysis (M/A). These complexes were supported on silica by a wet impregnation technique and used as catalysts in the liquid phase hydrogenation of cinnamaldehyde. The results obtained were contrasted with those from a 5 % palladium-on-silica catalyst, which was shown to produce hydrocinnamaldehyde and then phenylpropanol sequentially. The reactions of all of these catalysts took place on a hydrocarbonaceous over-layer which formed rapidly from unsaturated aldehydes and alcohols. The presence of diis over-layer was confirmed from mass balance calculations and elevated C and H % microanalysis measurements on used catalysts.