New Haven, Conn. — The world’s demand for alternative fuels and sustainable chemical products has prompted many scientists to look in the same direction for answers: converting carbon dioxide (CO₂) into carbon monoxide (CO).

But the labs of Yale chemists Nilay Hazari and James Mayer have a different chemical destination in mind. In a new study, Hazari, Mayer, and their collaborators present a new method for transforming CO₂ into a chemical compound known as formate — which is used primarily in preservatives and pesticides, and which may be a potential source of more complex materials.

The finding opens a new pathway for chemical discoveries, they say, and widens the possibilities for addressing environmental problems by transforming greenhouse gases into useful products.

The new study appears online March 7 in the journal Chem.

“Most of our fuels and commodity chemicals are currently derived from fossil fuels,” said Hazari, the John Randolph Huffman Professor of Chemistry, and chair of chemistry, in Yale’s Faculty of Arts and Sciences (FAS). “Their combustion contributes to global warming and their extraction can be environmentally damaging. Therefore, there is a pressing need to explore alternative chemical feedstocks.”

Hazari, who is also a member of the Yale Center for Natural Carbon Capture, and Mayer, the Charlotte Fitch Roberts Professor of Chemistry in FAS, are co-corresponding authors of the study. They are also part of the Center for Hybrid Approaches in Solar Energy to Liquid Fuels (CHASE), a federally funded solar energy research hub based at the University of North Carolina-Chapel Hill.

The challenges for transforming CO₂ into usable products — on an industrial scale — are formidable. Such processes require new catalysts that work under milder conditions (less extreme temperatures and pressures) and exhibit higher productivity and stability than currently available catalysts.

For the new study, the research team focused on a relatively under-explored type of catalytic system called an immobilized molecular catalyst. This is a system featuring a molecular catalyst that is attached to a solid support material.

The researchers developed molecular manganese catalysts that were attached to semiconducting, thermally oxidized porous silicon. When exposed to light, the silicon absorbs the light and transfers electrons to the manganese catalyst, which then converts CO₂ to formate.

“Formate is a very appealing product, as it is a potential stepping-stone to materials used industrially in very large quantities,” Mayer said. “Our work here opens the door to the use of readily available porous silicon as a support for molecular catalysts, in part because it establishes that the presence of a thin oxide layer improves catalyst selectivity and stability.”

The researchers had previously worked with hydride terminated porous silicon, said Eleanor Stewart-Jones, a graduate student in chemistry at Yale and co-lead author of the study.

“There’s a rich literature studying the modification of porous silicon surfaces,” she said. “Knowing that these surface modifications can be used to tune catalysis will hopefully be impactful for future hybrid catalysts using porous silicon.”

The researchers also noted that the discovery may have applications for catalysts that work with other chemical feedstocks, beyond CO₂.

The study’s other co-lead authors are Xiaofan Jia of Yale and former Yale researcher Young Hyun Hong, now of Sogang University in the Republic of Korea.

Co-authors from Yale are Abhishek Kumar, Justin Wedal, Jose Alvarez-Hernandez, Albert Gang, Noah Gibson, Madison Houck, Brandon Mercado, Hannah Nedzbala, Nicole Piekut, and Christine Quist. Additional co-authors are Carrie Donley from the University of North Carolina at Chapel Hill and Sungho Jeon, Jongbeom Kim, Hyeongjun Koh, Eric Stach, and Yihui Zhang of the University of Pennsylvania.

CHASE, an Energy Innovation Hub funded by the U.S. Department of Energy’s Office of Science, supported the research, along with the Yale Center for Natural Carbon Capture.