Surface characterization of supported Pd catalysts activated with chiral hydrogen donors

The activation of SiO2-supported Pd solids with chiral hydrogen donors such as (R)-(+)- or (S)-(-)limonene produces catalysts with a special feature, namely, the presence of metal-bound limonene species on the surface. A surf ace complex between limonene and Pd2+ ions is postulated from TPD/TCD, TPD/ MS, XPS, and C-13 CP/MAS NMR data. On the basis of the results, the configu ration of the stereosite in the hydrogen donor is not altered as the surfac e-binding interaction does not involve the asymmetric site in limonene.