Carbon dioxide or CO2 could potentially be used as a feedstock to be converted into carbon neutral “solar fuels” that store energy from the sun. But to compete with fossil fuels, the chemical reaction that carries out this conversion requires much more efficient catalysts. Researchers recently devised a photocatalyst structure with isolated single copper atoms in a polymer framework that radically improves the catalyst’s performance.
A description of the new catalyst was published in the magazine Nano-research†
There are a number of sectors, such as long-haul and aviation, which are difficult to electrify and thus in the battle for climate change, some form of carbon neutral fuel will have to be developed. In the meantime, solar energy can be low carbon, but is weather dependent. Sometimes not enough electricity is produced and sometimes too much.
An elegant solution that could solve both problems is the conversion of solar energy into synthetic fuels. By atmospheric CO. to bring down2 and by using it as a feedstock in combination with hydrogen produced by the splitting of water molecules, carbon neutral versions of hydrocarbons can be produced in a factory. This basically stores solar energy for later use when the sun isn’t shining or as a clean fuel that works in hard-to-electrify sectors (and beyond).
However, one of the major challenges to this vision of solar energy, which mimics how plants convert sunlight into energy, is to increase the efficiency of the chemical reactions involved enough to make the cost of the final product competitive with dirty ones. fossil fuels†
The key to achieving such efficiencies is to produce better catalysts, substances that speed up the chemical reaction. The main goal was to maximize the concentration of sites on catalyst molecules where a reaction can take place to improve efficiency while reducing waste.
Over the past decade, the catalysts research community has increasingly turned its attention to single-atom catalysts (SACs) with the aim of providing significant impetus to a variety of industrial processes, not just the photocatalysis needed for solar to -fuels . SACs are catalysts in which all metal atoms involved in the reaction are isolated single atoms spread on a sturdy support frame. These single metal atoms are also typically positively charged. Due to this unusual geometric and electronic structure:SACs can radically improve catalysis efficiency.
The field of SAC research and development has exploded in recent years, thanks in large part to the advent of advanced imaging and X-ray spectroscopic methods. This has allowed chemists to create highly detailed images of SACs in action even while the reaction is taking place, helping them better understand what’s happening and test new hypotheses. In addition, modern techniques of chemical synthesis have enabled the construction of very finely tailored SACs suitable for a desired process.
“In recent years, many different SACs for other chemical reactions have been developed, revolutionizing catalytic performance,” said Jiangwei Zhang, a co-author of the paper and a chemical physicist at the Advanced Chemical Engineering and Energy Materials Research. Center at the China University of Petroleum in Qingdao, “and now it was the turn of photocatalysts for solar fuel production.”
The researchers constructed a SAC with a covalent triazine-based framework structure (CTF) that anchors single copper atoms. CTFs are a relatively new class of polymers (series of very large molecules) that have already been shown to improve photocatalytic water splitting performance. By combining CTFs with single copper atoms, the chemists wanted to provide a highly porous structure (to increase the number of available sites where the relevant chemical reaction can take place) and deliver maximum atomic efficiency. They call this formulation Cu-SA/CTF.
They were able to visualize the single Cu atoms through high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) images. And the structure of sites where reactions take place was revealed by extensive X-ray Absorption Fine Structure (EXAFS) analyses.
With this information, the researchers were then able to test the performance of the Cu-SA/CTF photocatalysts and investigate what was happening at the atomic level. They found that the addition of the single copper atoms to the structure had given the catalysts an increased ability to adsorb CO2 (paste the CO2 on itself to carry out the chemical reaction), and enhanced the reaction to the visible light driving the process and delivering a number of other improvements. Together, this resulted in a significant improvement in the conversion of CO2 and water in methane fuel.
As a result, the researchers were able to develop guidelines for the atomic-scale design of other robust photocatalysts for the conversion of CO.2 in other useful substances.
Guocheng Huang et al, Spatial confinement of single copper atoms in covalent triazine-based frameworks for highly efficient and selective photocatalytic CO2 reduction, Nano-research (2022). DOI: 10.1007/s12274-022-4629-3
Provided by Tsinghua University Press
Quote: New catalyst radically increases conversion rate of carbon dioxide in solar fuels (2022, June 28) Retrieved June 28, 2022 from https://phys.org/news/2022-06-catalyst-radically-conversion-carbon-dioxide.html
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