Platinum-group metals (PGMs), i.e., Ru, Rh, Pd, Os, Ir, and Pt, are important in the catalysis of many industrially used reactions. Catalysts that contain one or two of these metals can catalyze many simple reactions well. However, more complex reactions with multiple proton- and electron-transfer processes require catalyst systems with a broader variety of active sites.
Dongshuang Wu, Kohei Kusada, Hiroshi Kitagawa, Kyoto University, Japan, and colleagues have developed nanoparticles that contain all six PGMs as catalysts for complex reactions. This type of material, with five or more elements in similar concentrations, is called a high-entropy alloy (HEA). HEAs, by their nature, have many different types of active sites. The team mixed solutions of RuCl3, RhCl3, K2PdCl4, OsCl3, K2PtCl4, and H2IrCl6 as metal precursors and added them to a solution of poly(N-vinyl-2-pyrrolidone) (PVP), which serves as a protecting agent, in triethylene glycol (TEG), which acts as solvent and reducing agent, at a temperature of 230 °C.
The resulting nanoparticles have a narrow size distribution, which was confirmed by transmission electron microscopy (TEM) imaging. Energy-dispersive X-ray spectroscopy (EDX) showed that the six metals are homogeneously distributed in the nanoparticles. The team tested the catalytic activity of the nanoparticles for the ethanol oxidation reaction (EOR), which involves a twelve-electron/twelve-proton transfer. The catalyst can promote this reaction and shows record activity—over 1.5 times higher than the best catalyst known so far. The team attributes this performance to the combination of all six PGM elements providing various adsorption sites, which allows the efficient catalysis of complex reactions.
- Platinum-Group-Metal High-Entropy-Alloy Nanoparticles,
Dongshuang Wu, Kohei Kusada, Tomokazu Yamamoto, Takaaki Toriyama, Syo Matsumura, Shogo Kawaguchi, Yoshiki Kubota, Hiroshi Kitagawa,
J. Am. Chem. Soc. 2020.