Supercritical catalytic cracking of n-dodecane over air-oxidized activated charcoal

The direct conversion of n-dodecane to light alkenes with an efficient catalyst can enhance the combustion efficiency and cooling performance of endothermic heat sinks for the development of propellants suitable for supersonic vehicles. In this work, a pretreated activated charcoal showed excellent performance as a novel cracking catalyst superior to the conventional ZSM-5 zeolite catalyst. Activated charcoal was oxidized at 298, 473, and 673 K, leading to surface modification, and n-dodecane cracking experiments were carried out at 4 MPa and 723 K. The activated charcoal exhibited a higher light alkene selectivity and heat sink capacity compared with the conventional ZSM-5. The charcoal oxidized at 673 K showed the highest light alkene selectivity of 28% among the tested catalysts, exceeding that of the reference ZSM-5 by 18%. The oxidizing pretreatment of the charcoal at high temperatures was found to generate carboxylic functional groups acting as Brӧnsted acid sites based on characterization by X-ray photoelectron spectroscopy, FT-IR, and temperature-programmed desorption with NH₃. The activated charcoal oxidized at 673 K had the largest amount of strong acid sites and Brӧnsted acid sites, which led to the highest conversion of n-dodecane and the selectivity of light alkene.