Catalytically Active Nanoporous Alloys

Alloying a metal may enable synergism, i.e., enhance or modify its properties such as the catalytic activity. Therefore, alloys (bimetallic in particular) attract considerable attention in the field of heterogeneous catalysis. Combining their catalytic potential with a high, nano-scale porosity, may produce new promising catalysts. Nevertheless, it is still considered a synthetic challenge to fabricate nanoporous alloys with uniform composition.

Herein, we present the use of previously reported^[i] technique to obtain nanoparticle clusters of cobalt-palladium (Co-Pd) or cobalt-ruthenium (Co-Ru) binary alloys in varying compositions. In This technique, microcrystalline bi-complex salts are synthesized by mixing two concentrated aqueous solutions of two counter-charge ionic metal complexes. Subsequently, salts are chemically reduced by hydrogen at up to 350° C to generate alloys. These alloys assemble as highly-porous (>90% porosity) nanoparticle clusters that preserve the stoichiometric ratio between the two different metallic elements in the salt, and the stereometric morphologies of their microcrystalline salts precursors. Data regarding the salts and alloys have been acquired using XRD, HR-SEM, FIB, and EDS characterization techniques.

Co-Pd alloys show catalytic activity in the semi-hydrogenation of phenyl-acetylene, which was used as a model reaction^[ii]. Co₂Pd₃ in particular achieve high conversion and selectivity (>90%) toward styrene. Most alloys have greater activity than their corresponding pure metals, a fact that indicates upon synergistic properties. Finally, alloys were easily separated from the reaction medium using a magnet, due to their magnetic properties attributed by the cobalt atoms.

Figure 1: Highly porous Co₂Pd₃ nanoparticles cluster (HR-SEM image)

^[i] M. Avisar-Levy, O. Levy, O. Ascarelli , I. Popov, A. Bino. Journal of Alloys and Compounds. 2015, 635, 48-54

^[ii] In cooperation with Prof. Raed Abu-Reziq`s Lab, Institue of Chemistry, the Hebrew University of Jerusalem