Complex Waste Stream Utilization for Hydrogen Evolution: Ammonia Borane Hydrolysis Over Red Mud Catalyst Under Mild Conditions

The utilization of red mud is a topic of significant interest due to its great production around the world, being the major by-product of alumina production. Nevertheless, its correct valorization is a matter of great complexity. In this work, we propose a novel use of red mud as a catalyst for the release of hydrogen from hydrolysis of ammonia borane in mild conditions. Ammonia borane is among the best chemical hydrogen carriers with a gravimetric hydrogen capability of up to 19 wt% but is characterized by a complex reactivity under thermal stimuli. Accordingly, ammonia borane hydrolysis has emerged as a solid route for direct and safe hydrogen release. In this work, we achieved complete hydrolysis of ammonia borane both at 30 °C and 40 °C after 660 s and 12 s, respectively, with a red mud loading of 10 wt%. The addition of red mud decreased the activation energy of the hydrolysis reaction over 90% and increased the kinetic constant over two orders of magnitude. Furthermore, red mud preserved the catalytic activity after three cycles with no significant changes.