Intermetallic Compound Pd2Ga as a Selective Catalyst for the Semi-Hydrogenation of Acetylene: From Model to High Performance Systems

A novel nanostructured Pd2Ga intermetallic catalyst is presented and compared to elemental Pd and a macroscopic bulk Pd2Ga material concerning physical and chemical properties. The new material was prepared by controlled coprecipitation from a single phase layered double hydroxide precursor or hydrotalcite-like compound, of the composition Pd0.025Mg0.675Ga0.3(OH)(2)(CO3)(0.15)center dot mH(2)O. Upon thermal reduction in hydrogen, bimetallic nanoparticles of an average size less than 10 nm and a porous MgO/MgGa2O4 support were formed. HRTEM images confirmed the presence of the intermetallic compound Pd2Ga and are corroborated by XPS investigations which revealed an interaction between Pd and Ga. Due to the relatively high dispersion of the intermetallic compound, the catalytic activity of the sample in the semihydrogenation of acetylene was more than 5000 times higher than observed for a bulk Pd2Ga model catalyst. Interestingly, the high selectivity of the model catalyst toward the semihydrogenated product of 74% was only slightly lowered to 70% for the nanostructured catalyst, while an elemental Pd reference catalyst showed only a selectivity of around 20% under these testing conditions. This result indicates the structural integrity of the intermetallic compound and the absence of elemental Pd in the nanosized particles. Thus, this work serves as an example of how the unique properties of an intermetallic compound, well-studied as a model catalyst, can be made accessible as real high-performing material allowing establishment of structure performance relationships and other application-related investigations. The general synthesis approach is assumed to be applicable to several Pd-X intermetallic catalysts, with X being elements forming hydrotalcite-like precursors in their ionic form.