(685f) Low Temperature and Pressure Ammonia Synthesis Via Highly Dispersed Ruthenium Based Catalysts

Ammonia synthesis is one of the most important chemical processes of the last 100 years due to its use as a fertilizer and, more recently, as a hydrogen storage and transportation vessel.¹ Currently, the industrial process to produce ammonia, the Haber-Bosch process, requires high pressure and temperature which results in high energy requirements. This process also typically uses methane as a hydrogen feedstock resulting in carbon dioxide emissions. Combining membrane reactors, renewable energy and nitrogen and hydrogen feedstocks of air and water could result in green ammonia production. Research into new ammonia synthesis catalysts is needed to operate at milder conditions that are compatible with membrane reactors, which typically demonstrate poor thermal stability.²

We investigated ruthenium-based catalysts with varied support materials for low temperature and pressure ammonia synthesis. A variety of support materials were synthesized, including MgO, Pr₂O₃, CeO₂, and inert diamond, and then impregnated with ruthenium. The catalysts were then tested for ammonia synthesis activity at temperatures below 400°C and pressures between 1-30 bar. The materials were characterized with electron microscopy, X-ray diffraction, chemisorption, physisorption and adsorption of probe molecules. This work led to a better understanding of the dispersion of ruthenium on the support before and after reaction and how particle size and metal-support interactions effects the ammonia synthesis rate.

1. Ogura, Y.; Sato, K.; Miyahara, S. I.; Kawano, Y.; Toriyama, T.; Yamamoto, T.; Matsumura, S.; Hosokawa, S.; Nagaoka, K. Efficient Ammonia Synthesis over a Ru/La0.5Ce0.5O1.75 Catalyst Pre-Reduced at High Temperature. Chemical Science 2018, 9 (8), 2230–2237.
2. McCullough, K.; Chiang, P. H.; Jimenez, J. D.; Lauterbach, J. A. Material Discovery and High Throughput Exploration of Ru Based Catalysts for Low Temperature Ammonia Decomposition. Materials 2020, 13 (8).