This image illustrates the process by which three metal elements (gold, silver, copper) are blended together to produce a trimetallic SNP. Image: Tokyo Tech.
This image illustrates the process by which three metal elements (gold, silver, copper) are blended together to produce a trimetallic SNP. Image: Tokyo Tech.

Due to their small size, nanoparticles find varied applications in fields ranging from medicine to electronics. This is because their small size gives them a high reactivity and semiconducting properties not found in bulk versions of the materials.

Sub-nanoparticles (SNPs) are even smaller than nanoparticles, with a diameter of around 1nm. Almost all the atoms in SNPs are available and exposed for reactions, which means SNPs are expected to have extraordinary functions beyond the properties of nanoparticles, particularly as catalysts for industrial reactions. However, preparing SNPs requires fine control over the size and composition of each particle on a sub-nanometer scale, making the application of conventional production methods near impossible.

To overcome this, researchers at the Tokyo Institute of Technology in Japan, led by Takamasa Tsukamoto and Kimihisa Yamamoto, developed the atom hybridization method (AHM). Using this method, it becomes possible to precisely control the size and composition of SNPs using a 'macromolecular template' known as a phenylazomethine dendrimer. Now, in a paper in Angewandte Chemie International Edition, the team reports taking their research one step further, by investigating the chemical reactivity of alloy SNPs obtained via AHM.

"We created monometallic, bimetallic and trimetallic SNPs [containing one, two or three metals respectively], all composed of coinage metal elements [copper, silver and gold], and tested each to see how good of a catalyst each of them is," explains Tsukamoto. The researchers tested the ability of these SNPs at catalyzing the oxidation reaction of olefins, compounds made up of hydrogen and carbon with wide industrial uses.

This revealed that the SNPs were stable and more effective than catalysts based on nanoparticles. Moreover, the SNPs showed a high catalytic performance even under mild conditions, in direct contrast to conventional catalysts, due to both the extreme miniaturization of their structures and the hybridization of different elements.

Monometallic, bimetallic and trimetallic SNPs demonstrated the formation of different products, and the hybridization or combination of metals showed a higher turnover frequency (TOF). The trimetallic combination Au4Ag8Cu16 showed the highest TOF because each metal element plays a unique role, and these effects work in concert to contribute to the SNP's high catalytic activity.

In addition, the SNPs selectively created hydroperoxide, a high-energy compound that cannot normally be obtained due to its instability. The SNPs did this by catalyzing mild reactions that resulted in the stable formation of hydroperoxide by suppressing its decomposition.

"We demonstrate for the first time ever, that olefin hydroperoxygenation can been catalyzed under extremely mild conditions using metal particles in the quantum size range," says Yamamoto. "The reactivity was significantly improved in the alloyed systems especially for the trimetallic combinations, which has not been studied previously."

These findings will prove to be pioneering for the discovery of innovative sub-nanomaterials made from a wide variety of elements, which should help to solve energy crises and environmental problems in years to come.

This story is adapted from material from the Tokyo Institute of Technology, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.