The Department of Chemistry was delighted to learn this February that Professor Douglas Stephan will be the 2024 recipient of The Catalysis Award.
A biennial award given by the Chemical Institute of Canada, the Catalysis Award is presented to an individual who, while residing in Canada, has made a distinguished contribution to the field of catalysis.
Stephan began his career at the University of Windsor, moving to the University of Toronto in 2008. He is recognized as a world-leading researcher in inorganic chemistry, and best known as the founder of the field of “frustrated Lewis pair” (FLP) chemistry.
“Some of our most important chemical reactions are about adding hydrogen to small molecules,” explained Stephan, in an interview about his body of work. “Adding it to nitrogen, for example, makes ammonia. All of these processes require a catalyst.”
A catalyst is a substance that accelerates a chemical reaction without itself being consumed in the reaction. Catalysts effectively reduce the energy barrier to a reaction, and usually have to be removed from the final product.
Stephan used another example: hydrogen is added to peanut butter to keep it from separating, and to do this requires a catalyst. The process adds hydrogen atoms to each of the carbon atoms of the carbon-carbon double bonds in the oil. The final product is a saturated oil which is a solid, making the peanut butter homogeneous and giving it an easy-to-spread texture and longer shelf life.
The use of transition metals like nickel, chromium and copper to effect the addition of hydrogen to double bonds has been well understood and in wide deployment for over a century. Indeed this process is crucial in everything from industrial food production and the pharmaceutical industry to refinement of crude oil and creation of plastics. Until recently, it was also believed that only the transition metals—which can be rare, expensive, hard to mine and toxic—could be used in these reactions.
This changed in 2006 when Stephan published a groundbreaking paper “Reversible, Metal-Free Hydrogen Activation” in Science. The paper, which has been cited over 2000 times, changed the way chemistry is taught, broadening the scope of catalysts well beyond transition metals.
Stephan and his coauthors showed that it was possible to create what he called "frustrated Lewis pairs (FLPs).” FLPs contain a Lewis acid and a Lewis base which are physically prevented from combining with each other and thus react with a third intervening substance. This allows such pairs to split hydrogen and react with a variety of other molecules.
Developing alternatives to traditional catalysts is an area of considerable focus at UofT Chemistry—Stephan mentioned Professor Robert Morris and his world-leading work in using more common metals, like iron, in these reactions. The significance of Stephan’s research, by contrast, takes a different direction, moving beyond transition metals in search of a way to make economically viable catalysts from substances containing nitrogen, phosphorus, boron or aluminum.
“This concept is new and researchers are developing new applications for it constantly. For example, one target is to use frustrated Lewis pairs to convert carbon dioxide into other useful substances. While this has been accomplished in principle, impacting on the earth’s overly carbon-rich atmosphere remains a challenge. Nonetheless, this is a fruitful new area of research.”
“We have 100 years of transition metals science,” Stephan continued. “Doing metal-free catalysis was something we thought was impossible, so FLPs have opened the door on chemistry we couldn’t do before.”
Stephan will give a talk about breaking developments in the FLP research area at the Canadian Society for Chemistry conference in Winnipeg this June.