Structural and catalytic properties of novel Au/Pd bimetallic colloid particles. EXAFS, XRD, and acetylene coupling

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. XRD 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 Au/Pd 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{111} and Au-modified Pd{111} and about the elementary steps involved in the conversion of reactants to products.