Metallic alloy nanoparticles are often used as catalysts in the production of industrial products such as fertilisers and plastics. Until now, only a small set of alloy nanoparticles have been available because of complications that arise when combining extremely different metals.
The technique, created by a team consisting of researchers from Johns Hopkins University, the University of Maryland, College Park, the University of Illinois at Chicago, and MIT, has reportedly made it possible to combine multiple metals, including those not usually considered capable of mixing.
Chao Wang, an assistant professor in the Department of Chemical and Biomolecular Engineering at Johns Hopkins University, said: “This method enables new combinations of metals that do not exist in nature and do not otherwise go together.”
The new materials, known as high-entropy-alloy nanoparticles, have created unprecedented catalytic mechanisms and reaction pathways and are expected to improve energy efficiency in the manufacturing process and lower production costs.
The new method uses shock waves to heat the metals to temperatures of 1700°C and higher at exceptionally rapid rates, both heating and cooling them in the span of milliseconds. The metals are melted together to form small droplets of liquid solutions at these high temperatures and are then rapidly cooled to form homogeneous nanoparticles. Traditional methods, which rely on relatively slow and low-temperature heating and cooling techniques, often result in clumps of metal instead of separate particles.
Based on these new nanoparticles, Prof Wang's research group designed a five-metal nanoparticle that demonstrated superior catalytic performance for selective oxidation of ammonia to nitrogen oxide, a reaction used by the chemical industry to produce nitric acid, which is used in the large-scale production of fertilisers and other products.
In addition to nitric acid production, the researchers are exploring the use of the nanoparticles in reactions like the removal of nitrogen oxide from vehicle exhaust.