<(From Left) Professor Sang Woo Han, Researcher Jin Wook Baek>
In chemical processes for producing pharmaceuticals, catalysts are a core technology that determines production speed and cost. However, until now, there has been a trade-off between "precise but disposable catalysts" and "reusable catalysts." A KAIST research team has developed an eco-friendly catalytic technology that combines these two types, operating solely with light and air. This opens a pathway to producing pharmaceutical ingredients more cheaply and cleanly, with expected reductions in carbon emissions and environmental pollution.
KAIST (President Kwang Hyung Lee) announced on the 30th of March that a research team led by Professor Sang Woo Han of the Department of Chemistry has succeeded in combining two different types of catalysts into one system. One is a silver (Ag)-based catalyst that operates in a solid state, and the other is an organic photocatalyst, DDQ (a substance that triggers chemical reactions upon absorbing light), which operates in solution. By enabling these two catalysts to function together, the team made it possible to carry out previously difficult reactions more efficiently.
< Schematic diagram of the operation of a heterogeneous–homogeneous hybrid photocatalytic system >
Using this technology, the researchers successfully produced amines—key raw materials for pharmaceuticals—through an environmentally friendly process using only sunlight and air. This demonstrated that the desired substances can be synthesized without additional chemical reagents, proving the practicality of the technology.
Conventional organic photocatalysis required additional chemicals to reuse catalysts after reactions, or suffered from reduced efficiency due to slow reaction rates when using oxygen from air.
To address this, the research team proposed a method of reusing byproducts generated during the reaction. These byproducts restore the catalyst to a reusable state, while oxygen in the air helps sustain this cycle. In other words, instead of being used once and discarded, the catalyst regenerates itself and continues operating in a "cyclic system."
As a result, they established a "cyclic catalytic system" that continues functioning without the need for additional chemical inputs. Notably, this system operates solely with sunlight and air. Sunlight activates the catalyst to initiate the reaction, while air restores the used catalyst to its active state. In essence, the catalyst continuously "recharges" and operates repeatedly. Since air leaves only water as a byproduct in this process, the environmental burden is significantly reduced.
In addition, to solve the issue of reduced performance when different catalysts interact, the team introduced lithium salt (LiClO₄). This substance helps regulate interactions between the two catalysts, significantly improving their stability and lifespan.
< A hybrid catalyst powered by light and air as energy sources >
Professor Sang Woo Han stated, "This research is the first to successfully integrate an inorganic photochemical loop system—where a metal-based catalyst reacts under light and returns to its original state—into the field of precise organic synthesis," adding, "It represents an important advancement that combines only the advantages of different catalytic systems to dramatically reduce the carbon footprint of the chemical industry." He further noted, "It opens a new pathway for producing high-value compounds, such as pharmaceutical ingredients, in the most environmentally friendly way."
This research was conducted with Jin Wook Baek of the KAIST Department of Chemistry as the first author, and the results were published on March 18 in the Journal of the American Chemical Society (JACS), a leading journal in chemistry.
※ Paper title: "Merger of heterogeneous and homogeneous photocatalysis for arene C–H Amination"
※ DOI: 10.1021/jacs.5c20824
This research was supported by the National Research Foundation of Korea's Mid-career Researcher Program.
