An inexpensive tin-based catalyst can selectively convert carbon dioxide into three commonly produced chemicals: ethanol, acetic acid, and formic acid. Carbon dioxide (CO2) is an untapped resource hidden in emissions from many industrial activities. A source of greenhouse gases and global warming, it can be captured and converted into value-added chemicals.

In a joint 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 convert CO2 into ethanol, acetic acid, or formic acid. These liquid hydrocarbons are among the most produced chemicals in the United States and are found in many commercial products. For example, ethanol is a major ingredient in many household products and an additive in nearly all American gasoline.

Electrocatalytic conversion method

The method the team used is called electrocatalytic conversion, which is CO conversion. ₂ It takes place with the help of electricity on the catalyst. The team was able to control CO conversion by varying the size of tin used, from single atoms to ultra-small clusters and larger nanocrystals. ₂ It is converted into acetic acid, ethanol and formic acid, respectively. The selectivity of each of these chemicals was 90% or higher. “Our discovery that the reaction pathway varies depending on the size of the catalyst is unprecedented,” Liu said.

Computational and experimental studies have shown various insights into the reaction mechanisms of the formation of the three hydrocarbons. An important finding was that the reaction pathway was completely changed as the normal water used for the conversion was converted to deuterated water (deuterium is an isotope of hydrogen). This phenomenon is known as the kinetic isotope effect. This has not been seen before in CO2 conversion.

Two user facilities of the U.S. Department of Economics’ Office of Science at Argonne – the Advanced Photon Source (APS) and the Center for Nanoscale Materials (CNM) – participated in this research. “Using the hard X-ray beams available at APS, we recorded the chemical and electronic structure of tin-based catalysts with different tin contents,” said Argonne physicist Chenjun Sun. In addition, the high spatial resolution possible with transmission electron microscopy at CNM directly imaged the arrangement of tin atoms from single atoms to small clusters with different catalyst loadings.

According to Liu, ​“Our ultimate goal is to use locally generated electricity from wind and solar to produce desired chemicals for local consumption.”

This will require the integration of newly discovered catalysts into a low-temperature electrolyzer to convert CO2 using electricity supplied from renewable energy sources. Low temperature electrolyzers can operate at ambient temperature and pressure. This enables rapid starting and stopping to ensure intermittent supply of renewable energy. This is an excellent technology for this purpose.

“If we can selectively produce only the chemicals needed near the site, we can help reduce CO2 transportation and storage costs,” Liu said. “This would truly be a win-win situation for those who adopt our technology locally.”