Characterization of palladium surfaces with (+)-apopinene: Correlation of reaction paths with surface features

The molecular probe (+)-apopinene is chosen for the characterization of metal surface sites because of its unique structural features. These features allow clear distinctions of adsorption side and double bond position. By measuring the relative rates of double bond migration and addition, k i k a , it is shown that (+)-apopinene is sensitive to 17 different Pd catalyst preparations. Among these, a set of alumina-supported Pd catalysts ranging in dispersions from 0.055 to 1.00 (131 to 8.4 A by EM) yielded results consistent with the notions that 3M-type sites (highly coordinatively unsaturated) catalyze principally addition and 2M-type sites catalyze principally isomerization. (+)-apopinene distinguishes between reduced PdO2 samples which have undergone different extents of Surface reconstruction.