(459b) Using Lanthanides to Improve Ammonia Catalysts

Ammonia has been suggested as a hydrogen carrier for fuel purposes. Here, ammonia can be produced when energy is readily available, and decomposed to hydrogen- for combustion- and nitrogen- which can be safely released to the environment unlike organic hydrogen carriers. Advancements must be made for roll-out, though, as the current catalysts operate at too harsh of conditions for fuel purposes. To counter this, we produced novel ruthenium-based ammonia synthesis catalysts supported on praseodymium oxide.¹ During this, we completed a screening finding that barium and cesium were the best promoters, as expected, but found that dysprosium and lutetium were also beneficial.

Using this knowledge, we have produced novel dysprosium-praseodymium mixed metal oxide supports and tested these catalysts for ammonia synthesis and ammonia decomposition reactions. Through doping dysprosium, it was possible to increase the reaction rate for ammonia decomposition by about 30% while improving the stability of the catalysts, and were able to improve the ammonia synthesis reaction rate by 2.5 times. To determine the cause of this, TPR, RAMAN, XRD and CO-DRIFTS were all utilized. In addition, lutetium was tested as a promoter for ammonia synthesis. The inclusion of lutetium, when added with potassium, to a baseline barium-cesium promoted catalyst led to an increase in activity by approximately 25% when compared to the typical barium-cesium only promoted catalyst. Determination of the role of the lutetium was conducted using detailed kinetic evaluation, in situ spectroscopy and chemisorption. Overall, these new catalysts have opened opportunities for utilization of ammonia as a hydrogen carrier.

¹Drummond, S.M.; et al. Promoted Ru/PrO_x Catalysts for Mild Ammonia Synthesis. Catalysts 2024, 14, 572. https://doi.org/10.3390/catal14090572