Conversion of Room Temperature from CO2 to CO
New methods have the potential to reduce carbon dioxide emissions into the atmosphere and lower the cost of chemical reactions.
Researchers at the National Institute of Standards and Technology (NIST) and their colleagues have demonstrated room temperature methods that can significantly reduce carbon dioxide levels in fossil fuels, one of the major sources of carbon emissions in the atmosphere.
Although researchers have demonstrated this method on a small scale, enormously controlled environments measuring only nanometers (billions of meters), they have come up with the concept to improve their methods and make them practical for real-world applications.
In addition to offering new ways to mitigate the effects of climate change, the chemical processes used by scientists can also reduce the costs and energy requirements to produce liquid hydrocarbons and other chemicals used by industry. That is because the side effects of our method include building blocks to synthesize methane, ethanol and other carbon-based compounds used in industrial processing.
The team tapped a novel energy source from nanoworld to trigger a run-of-the-mill chemical reaction that eliminates carbon dioxide. In this reaction, solid carbon latches into one of the oxygen atoms in the carbon dioxide gas, reducing it to carbon monoxide. Conversion usually requires a significant amount of energy in the form of high heat – a temperature of at least 700 degrees Celsius, hot enough to melt aluminum at normal atmospheric pressure.
Instead of heat, the team relied on the energy harvested from traveling electron waves, known as local surface plasmon (LSPs), which attach to their respective aluminum nanoparticles. The team triggers the LSP oscillation by exciting the nanoparticles with electron beams whose diameter can be adjusted. Narrow beams, about a nanometer in diameter, bomb each aluminum nanoparticle, while beams about a thousand times larger produce LSP among a set of large nanoparticles.
In team experiments, aluminum nanoparticles were placed in a layer of graphite, a carbon form. This allows nanoparticles to transfer LSP energy into graphite. In the presence of carbon dioxide gas, which the team injects into the system, graphite plays the role of extracting individual oxygen atoms from carbon dioxide, reducing carbon monoxide. Aluminum nanoparticles are stored at room temperature. In this way, the team achieves a major achievement: get rid of carbon dioxide without the need for high heat sources.
Advance methods for removing carbon dioxide have had limited success because the technique requires high temperatures or pressures, expensive precious metal work, or poor efficiency. In contrast, the LSP method not only saves energy but also uses aluminum, cheap metals and more.
Although LSP reactions produce toxic gases – carbon monoxide – gases are easily combined with hydrogen to produce essential hydrocarbon compounds, such as methane and ethanol, which are commonly used in industry, says NIST researcher Renu Sharma.
He and his colleagues, including scientists from the University of Maryland at College Park and DENSsolutions, in Delft, the Netherlands, report their findings in Natural Materials,
“We suggest that the first for this carbon dioxide reaction, the rest of which will only occur at 700 degrees C or higher, can be triggered using LSP at room temperature,” said researcher Canhui Wang of NIST and the University of Maryland.
Researchers chose electron beams to excite LSP because beams can also be used to draw structures in systems as large as several billion meters. This allows the team to estimate how much carbon dioxide has been released. They studied the system using a transmission electron microscope (TEM).
Due to the low carbon dioxide concentration and reaction volume, the team had to take specific steps to directly measure the amount of carbon monoxide produced. It is performed by attaching a specially modified gas cell container from TEM to a gas chromatograph mass spectrometer, allowing the team to measure part-per-millions of carbon dioxide concentrations.
Sharma and her friends also used images generated by electron beams to measure the amount of graphite engraved in the experiment, proximizing how much carbon dioxide was taken. They found that the ratio of carbon monoxide to carbon dioxide measured at gas cell container outlets increased linearly with the amount of carbon emitted by ethics.
Electron beam imaging also confirms that most carbon emissions – a proxy for carbon dioxide reduction – occur near aluminum nanoparticles. Further research reveals that when aluminum nanoparticles are not in the experiment, only about seven-sevenths of carbon are engraved.
Limited by electron beam size, small team experimental system, only about 15 to 20 nanometers across (small virus size).
For scale-up systems that can remove carbon dioxide from commercial power plant exhausts, light rays can be a better option than electron beams to excite LSP, Wang said. Sharma suggested that transparent fences containing carbon nanoparticles and packed aluminum could be stored at the power plant. The array of light beam beams mounted on the grid will activate LSPs. When the exhaust penetrates the device, the LSP activated by the light in the nanoparticles will be energized to remove carbon dioxide.
Aluminum nanoparticles, which are commercially available, should be evenly distributed to maximize contact with incoming carbon and carbon dioxide sources, the team noted.
Recent work also suggests that LSP offers a way for other chemical reactions that currently require large amounts of energy infusion to occur at temperatures and pressures commonly used with plasmonic nanoparticles.
“Reducing carbon dioxide is an important issue, but it would be a bigger deal, saving a lot of energy, if we could start a chemical reaction at room temperature that now requires heating,” said Sharma.
References: “Endothermic reactions at room temperature activated by ultra-ultraviolet plasmons” by Canhui Wang, Wei-Chang D. Yang, David Raciti, Alina Bruma, Ronald Marx, Amit Agrawal and Renu Sharma, November 2, 2020, Natural Materials,
DOI: 10.1038 / s41563-020-00851-x