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The structure, stability, and catalytic properties of an unusual bimetallic colloid having a well-defined Au core/Pd shell structure are reported. This material is an efficient catalyst for coupling and cyclization of acetylene, even at room temperature. X R D data and in situ EXAFS data combined with reaction studies reveal how large changes in activity and selectivity correlate with controlled variations in the degree of thermally induced A u P d intermixing. Increasing the Au content of the surface results in a large increase in overall activity and a pronounced increase in the selectivity for benzene formation relative to n-hexane. These findings may be rationalized very satisfactorily in the light of single-crystal data which provide information about the bonding and reactivity of acetylene and benzene on Pd(ll1) and Au-modified Pd(ll1) and about the elementary steps involved in the conversion of reactants to products.

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