(617ho) A Cost-Free Catalyst for COx-Free Hydrogen Production: Utilization of Red Mud for Ammonia Decomposition

Here we utilize red mud (RM), a by-product of the Bayer process for aluminum production (produced up to 2.5 ton for each ton of aluminum produced), as an ammonia decomposition catalyst to present an almost cost-free catalyst as a green alternative to the high-cost Ru-based catalysts. Upon acid digestion at different conditions followed by calcinations at different temperatures modified red mud (MRM) samples with different chemical composition and physical properties were obtained. Data measured for ammonia decomposition on these MRM samples show high and stable hydrogen production rates. For instance, an MRM sample prepared by acid digestion of RM at 220 °C in HCl followed by reduction at 700 °C showed stable hydrogen production rates of 72 and 196 mmol H₂min^-1 g_cat^-1 for more than 72 h at 700 °C measured at the corresponding space velocities of 72 000 and 240 000 cm³ NH₃ h^-1 g_cat^-1, respectively. These results are the highest ever reported for a non-noble metal catalyst for stable hydrogen production from ammonia. Detailed characterization of the samples revealed that Fe₃N species formed by the conversion of metallic iron during the induction period are the active species for the reaction. Data further indicate that there is a direct correlation between the size of Fe₃N nanoparticles and the hydrogen production rate. These results offer a clean solution for the utilization of one of the most hazardous and highly-produced industrial wastes for generating CO_x-free clean energy.

This work is supported by the Scientific and Technological Research Council of Turkey (TUBITAK), 1003-Primary Subjects R&D Funding Program (Project number: 213M028). A.U. acknowledges the BAGEP Award of the Science Academy of Turkey. We thank Koç University Surface Science and Technology Center (KUYTAM) for help with sample characterization.