Liquid-Organic hydrogen carriers as endothermic fuels

Some cyclic molecules have been proposed as liquid-organic hydrogen carriers (LOHC) due to their ability to undergo dehydrogenation reversibly, with ones containing nitrogen in the ring showing special stability. Here, we examined one of these, 1,2,3,4-tetrahydroquinoline (THQ), for use as an endothermic fuel for thermal protection of hypersonic aircraft engines. The conversion and endothermic heats of reaction were measured over a Pd-Al2O3 catalyst at 60 bar and temperatures between 500 and 600 C. Heats of reaction as large as 950 kJ kg(-1) were obtained, with conversions greater than 80% at 600 degrees C. The catalyst was stable over a period of at least several hours and no coking was observed. For comparison, the reaction of methylcyclohexane formed tars that quickly blocked the reactor, even at 500 degrees C on this catalyst. These results suggest that LOHC could serve as alternative fuels for endothermic cooling.