Study Finds Organic Crystals that Can Trap Nitrous Oxide, a Toxic Greenhouse Gas

Even though nitrous oxide (N₂O) is a greenhouse gas that greatly contributes to global warming, gas separation technology has mostly focused on carbon dioxide. Now, scientists from Korea Maritime and Ocean University are exploring a new concept for N₂O separation using an organic compound called hydroquinone clathrate. They found that this compound can selectively trap either N₂O or nitrogen gas (N₂) depending on its crystalline structure, paving the way for a cost-effective N₂O/N₂ separation technology.

​​​​​​​When speaking of global warming and greenhouse gases, people immediately think of carbon dioxide (CO₂) as the main villain. However, the truth is that there are other gases produced by human activities that are much worse. Such is the case for nitrous oxide (N₂O), which has received less attention in spite of its 300-fold greater impact on global warming than CO₂. “Gas separation technology focusing on CO₂ has been the subject of much study, whereas the corresponding research on N₂O recovery remains insufficient,” remarks Prof. Jiho Yoon from Korea Maritime and Ocean University.

Prof. Yoon’s research group has been focused on finding a feasible and energy-effective approach to separate and capture N₂O from gas mixtures found in today’s industries. In their latest study, which was published in Environmental Science and Technology, they presented a new concept for greenhouse gas separation using hydroquinone (HQ) clathrate. Clathrates are a type of crystalline compound in which small molecules called guests are trapped inside appropriately sized holes or cages formed by host molecules.

Using a wide variety of techniques, including X-ray diffraction, scanning electron microscopy, Raman spectroscopy, and nuclear magnetic resonance, the scientists fully characterized two of the main crystalline forms of HQ, called α-HQ and β-HQ. They also analyzed the gas storage capacity and formation kinetics of both types, shedding light on the structure-driven selectivity of each form towards different gases.

It turns out that HQ clathrate behaves markedly differently depending on the concentration of N₂O when subjected to a N₂O/N₂ mixture. For an N₂O concentration below 20%, α-HQ traps only nitrogen (N₂) molecules, acting like a highly selective molecular sieve. Conversely, when exposed to higher concentrations of N₂O, α-HQ transforms into β-HQ, which primarily encages N₂O molecules. Inspired by this newly found dual-function—or “Janus”— behavior of HQ clathrate, the scientists developed a novel concept for greenhouse gas separation. Their stepwise process involves using β-HQ across multiple chambers to sequentially obtain a purer and purer N₂O, reaching a final concentration of about 97%. Meanwhile, α-HQ can be used to remove N₂ from gas mixtures to help reach the initially required N₂O concentration above 20%.

This study marks the first time an organic clathrate was used for N₂O separation. Prof. Yoon highlights that their novel approach is applicable at room temperature and atmospheric pressure, which would make its adoption more feasible in the industry. “Our approach to N₂O separation via clathrate formation may offer the dual benefits of greenhouse gas control and considerable energy savings, making it a promising option in terms of energy consumption and capital cost,” he concludes.

Let us hope that this technology is further developed, in order to secure a better future for our planet.