Trying to catch a ball with a stiff hand is awkward at best and ineffective at worst. The same principle applies to single-atom catalysts (SACs), where reaction-boosting atoms sit isolated within a rigid molecular framework. When these active sites are locked too tightly in place, they struggle to flex, bind and activate the chemicals (substrates) they are meant to transform.
“Typical SACs are stabilised by nearly saturated, symmetrically coordinated environments,” noted Shibo Xi, a Senior Scientist II at the A*STAR Institute of Sustainability for Chemicals, Energy and Environment (A*STAR ISCE²). “While this configuration makes them very thermodynamically stable, it also limits their tunability and catalytic activity.”
Now, Xi and colleagues at A*STAR ISCE², the National University of Singapore (NUS) and universities in China have found a way to give SACs a more relaxed grip. Led by Jiong Lu of NUS, the team investigated whether desaturating SACs—reducing the number of molecular bonds tying them to supporting molecules—would create catalysts with stable, yet more accessible active sites.
The key step in the team’s process was potassium hydroxide (KOH)-mediated Joule thermal shock. “The catalyst undergoes a rapid, highly controlled reshaping driven by electricity and an alkaline chemical,” Xi explained. “A brief electrical pulse heats it almost instantaneously—in just a few milliseconds—while KOH helps subtly rearranges and ‘etches’ the structure at high temperature. The result is a stable metal atom that is more exposed, making it easier for reactants to reach.”
As a proof of concept, the team produced several desaturated (De-sat) copper-based SACs, testing their performance in catalysing propargylic substitution reactions—vital steps in producing complex molecules that are common to many high-value products. “For example, such reactions play an important role in synthesising certain anti-inflammatory and neurological drugs,” noted Xi.
The team reported that their De-sat copper SACs demonstrated remarkable catalytic activity with diverse substrates in propargylic substitution reactions. Molecular fragments from drugs such as fluoxetine, maprotiline and naftifine proved compatible with the system, with yields as high as 94 percent. The catalysts also showed almost no degradation after five consecutive reaction runs.
“Compared with traditional homogeneous catalysts, De-sat SACs are more stable, environmentally friendly and cost-effective,” said Xi. “Under certain conditions, they can also exhibit completely different selectivity, allowing the same reactions to produce different products.”
Xi added that while homogeneous SAC systems also often suffer from residual metal contamination in fine chemicals or drug molecules, De-sat SACs can effectively minimise metal residues in final products.
As efforts to scale up and optimise their system for industrial production continue to advance, Xi remains optimistic about its prospects. “Such an approach holds great promise for creating desaturated yet robust SACs that could tackle challenging organic transformations in the future,” said Xi.
The A*STAR-affiliated researchers contributing to this research are from the A*STAR Institute of Sustainability for Chemicals, Energy and Environment (A*STAR ISCE²).
