Sustainable carbon from chitosan: a new support material for ammonia cracking
Sustainably produced Ammonia is considered one of the most promising chemical hydrogen carriers for a global H₂ trade. Recovering hydrogen produced with lower carbon footprint from it, however, requires sustainable catalysts that crack ammonia at the lowest possible temperatures. For the first time, a team from Fraunhofer ISE together with KIT and Kiel University demonstrates that carbon supports derived from the renewable biopolymer chitosan are well suited for this purpose – sourced from chitin, which is available at roughly 6 million tonnes per year as biomass waste.
The supports were produced by hydrothermal carbonisation (HTC) followed by pyrolysis at 600 °C and 1000 °C, and loaded with only 1 wt% ruthenium. The key to performance lies in surface chemistry: the pyrolysis temperature controls the type and amount of oxygen and nitrogen surface groups – and thereby the distribution, reducibility and crystallinity of the Ru nanoparticles. Whereas untreated HTC-based carbon causes pronounced Ru agglomeration, the pyrolysed supports achieve uniform metal distribution and up to a 14-fold higher conversion rate in ammonia decomposition: more than 50 % NH₃ conversion already at 450 °C, outperforming a catalyst based on commercial activated carbon. The support pyrolysed at 1000 °C also excels in stability, maintaining constant conversion close to the reaction maximum/equilibrium for 72 hours at 500 °C with significantly lower mass loss due to suppressed side reactions, i.e., methanation of the support material.
The work was carried out within the AmmoCatCoat project, funded by the German Federal Ministry of Research, Technology and Space (BMFTR).
