Lurking within the emissions from many industrial operations is an untapped resource — carbon dioxide. A contributor of greenhouse gas and global warming, it could instead be captured and converted to value-added chemicals.
In a collaborative project involving the U.S. Department of Energy’s (DOE) Argonne National Laboratory, Northern Illinois University and Valparaiso University, scientists report a family of catalysts that efficiently converts carbon dioxide into ethanol, acetic acid or formic acid. These liquid hydrocarbons are among the most produced chemicals in the U.S. and are found in many commercial products. For example, ethanol is a key ingredient in numerous household products and an additive to nearly all U.S. gasoline.
The catalysts are based on tin metal deposited over a carbon support.
“If fully developed, our catalysts could convert the carbon dioxide produced at various industrial sources to valuable chemicals,” said UChicago Pritzker School of Molecular Engineering Senior Scientist and Argonne National Laboratory Senior Chemist Di-Jia Liu. “These sources include fossil fuel power plants and bio-fermentation and waste treatment facilities.”
The method used by the team is called electrocatalytic conversion, meaning that carbon dioxide conversion over a catalyst is driven by electricity. By varying the size of tin used from single atoms to ultrasmall clusters and also to larger nano-crystallites, the team could control the carbon dioxide conversion to acetic acid, ethanol and formic acid, respectively. Selectivity for each of these chemicals was 90% or higher.
“Our finding of a changing reaction path by the catalyst size is unprecedented,” Liu said.
Computational and experimental studies revealed several insights into the reaction mechanisms forming the three hydrocarbons. One important insight was that the reaction path completely changes when the ordinary water used in the conversion is switched to deuterated water (deuterium is an isotope of hydrogen). This phenomenon is known as the kinetic isotope effect. It has never been previously observed in carbon dioxide conversion.