Non-CO2 greenhouse gases removal through photocatalysis
The rate of climate change can be slowed down by reducing the levels of methane (CH4), carbon dioxide (CO2) and other greenhouse gases (GHGs) in the atmosphere. However, until now little attention has been given to the removal of atmospheric non-CO2 GHGs. Global warming potential (GWP) is a measure of the potency of GHGs. The three most important non-CO2 GHGs – CH4, nitrous oxide (N2O) and dichloro-difluoromethane (CCl2F2)(opens in new window) – all have a high GWP. These high GWP gases can be eliminated by photocatalysis(opens in new window), transforming them into benign atmospheric gases, water vapour and small amounts of volatile compounds, which are much less potent GHGs than their precursors. The photocatalytic processes, which have proven highly effective at the laboratory scale, allow scientists to harness sunlight to promote the destruction of CH4, N2O and CCl2F2.
Driven by the sun
With the support of the Marie Skłodowska-Curie Actions programme(opens in new window), the STEPforGGR(opens in new window) project, tested whether this innovative approach to GHG removal technology can work under real-world conditions. Researchers employed solar up-draft towers(opens in new window) as giant ‘air processors’ together with photocatalysis to eliminate non-CO2 GHGs, particularly methane, directly from air. Solar up-draft towers use the sun to warm air under a large collector (like a greenhouse). The warm air rises through a tall chimney, creating a continuous, passive airflow without the need for fossil energy. This airflow is the crucial ‘enabler’, bringing enormous volumes of air into controlled contact with catalytic surfaces. “Air is moved through a sun‑heated system, and the target gas (for example methane) encounters a special coated surface. Under light, this coating helps trigger chemical reactions that convert the greenhouse gas into less climate‑active products. For methane, these are mainly CO2 and water,” explains project coordinator Wei Li from the University of Edinburgh(opens in new window). “Methane is much more potent than CO2 over short timescales. Thus, converting small amounts of methane can still produce a meaningful climate benefit, especially if done at very large scale,” Wei Li observes.
From lab to large scale
Scaling up requires combining very large passive airflow systems (up-draft towers or related concepts) and manufacturable coated materials that remain active outdoors over long periods. Practical applications involve large installations in sunny regions where land availability and airflow are favourable and potentially share a location with other infrastructure. According to Wei Li: “Atmospheric methane removal by photocatalysis is not just a materials challenge or just a reactor problem. It is a coupled system where airflow, light delivery, surface chemistry and outdoor durability all interact. STEPforGGR demonstrated how to analyse these interactions systematically, and where the real performance limits emerge.” Next steps are expected to focus on improving catalyst activity and long-term durability, plus engineering designs that maximise contact while limiting pressure losses. The goal is to translate laboratory performance into robust techno‑economic and land‑use scenarios. “There is also scope for exploring related architectures (including building-integrated or alternative tower concepts) and to extend the research from methane towards other non‑CO2 gases where feasible,” Wei Li concludes. This work will benefit researchers and engineers developing greenhouse gas removal technologies, industries involved in reactor and materials manufacture, such as those producing coated glass, and policymakers evaluating credible options for climate mitigation.
