Single-Atom Catalyst Unlocks Lignin's Hidden Chemical Value

Lignin gives plants much of their structural strength and is the largest renewable source of aromatic compounds found in nature. It can make up as much as 35% of the waste biomass left over from agriculture and forestry. But lignin's complex molecular structure makes it notoriously difficult to break apart efficiently, which has limited its use in sustainable manufacturing.

In a study published in the journal ACS Catalysis, an international team that included Dr. Christopher Parlett, Xinyue Zhou and Yutao Jiang from the Department of Chemical Engineering developed a highly efficient "single-atom catalyst" and worked out, at the molecular level, how it breaks the strong bonds holding lignin together. The catalyst is made of individual ruthenium atoms embedded in a nitrogen-doped carbon material; keeping the atoms isolated lets it deliver strong performance while using only very small amounts of metal, improving efficiency over conventional catalytic systems.

Using a combination of laboratory experiments and computational modelling, the researchers found that a specific atomic arrangement, called a "Ru-N4 site," is especially important. These sites activate oxygen molecules, producing highly reactive species. Those species then attack the lignin structure, triggering the breaking of both carbon-oxygen and carbon-carbon bonds and splitting lignin into smaller molecules.

Under optimized conditions, the catalyst converted nearly all of the model lignin compounds tested and produced high yields of valuable products, including phenol, while working under relatively mild conditions without harsh chemicals. Tested further on real lignin from several biomass sources, it successfully converted them into useful aromatic compounds that could become building blocks for fuels, plastics and other materials. The findings give a detailed picture of how single-atom catalysts work during biomass conversion and could guide a shift toward a more circular, biomass-based chemical industry.

"Understanding exactly how these catalysts work at the atomic level allows us to design better materials for converting renewable resources into valuable chemicals," said Dr. Christopher Parlett, Lecturer in Chemical Engineering.