Novel catalysts to address overheating in hypersonic aircraft
Researchers at Australia's RMIT University have developed 3D-printed catalysts to address the challenge of overheating in hypersonic aircraft and possibly other industrial processes.
The aeronautical community is currently researching technology that could lead to the development of a fleet of commercial hypersonic transport. This new generation of aircraft would allow passengers to fly across the Atlantic or the Pacific Ocean in just 2-3 hours at Mach 5–8 speeds (approximately 6,100 to 9,800km per hour). The potential impact on the chemical composition of the atmosphere of a future fleet of hypersonic aircraft will depend on various factors, including the fuel consumption by each aircraft, the type of fuel used, and the emission indices for the various effluents released by the engines. 
So far, only a few experimental aircraft have reached hypersonic speed. Their development still raises many challenges, such as the resulting extreme heat levels. For aircraft traveling at more than five times the speed of sound, friction between the aircraft and outside air generates tremendous amounts of heat. The use of endothermic fuels represents a promising experimental approach to tackling this overheating issue. Endothermic fuels can act as both the propellant and the primary cooling agent of the aircraft.
According to researchers at Australia's RMIT University, fuels capable of absorbing heat while powering an aircraft require highly efficient catalysts in order to achieve the required chemical reactions.  In this scenario, a heat exchanger of some kind would capture heat from overheating aircraft parts and transfer it to a cool hydrocarbon fuel. As the fuel warms up to a certain temperature, it triggers chemical reactions that break down the hydrocarbons into simpler units. These can then be used for propulsion.  Roxanne Hubesch, lead author of the study, explains that “additionally, the heat exchangers where the fuel comes in contact with the catalysts must be as small as possible, because of the tight volume and weight constraints in hypersonic aircraft.” 
To make the new catalysts, the team used 3D printing to produce tiny heat exchangers made of metal alloys and coated them with synthetic minerals known as zeolites. Through laboratory testing, the researchers replicated the extreme temperatures and pressures experienced by the fuel at hypersonic speeds.
Further development is still needed, for instance to identify the best combination of metal alloys. The researchers hope that this new generation of catalysts could be used to transform any industrial process where overheating is an ever-present challenge. They also hope to extend the potential applications of their work to air pollution control for vehicles and miniature devices to improve indoor air quality.
 Kinnison, D., Brasseur, G. P., Baughcum, S. L., Zhang, J., & Wuebbles, D. (2020). The impact on the ozone layer of a potential fleet of civil hypersonic aircraft. Earth's Future, 8(10), e2020EF001626. https://doi.org/10.1029/2020EF001626
 Next gen 3D printed catalysts to propel hypersonic flight. https://www.rmit.edu.au/news/media-releases-and-expert-comments/2021/sep/3d-printed-catalysts-hypersonic