Ammonia-ship exhaust catalysts reach 99% removal in lab tests

Ammonia has emerged as a fuel that emits little greenhouse gas when burned, which is why shipping is looking at it. Its exhaust is another matter. At the Korea Institute of Energy Research (KIER), a team led by Dr. Sun-Mi Hwang has developed catalysts that, in lab tests, remove about 99% of the targeted pollutants from that exhaust.

The problem is what leaves the stack. Burning ammonia produces nitrogen oxides (NOx), unburned ammonia and nitrous oxide (N2O), a greenhouse gas with a warming potential roughly 300 times that of carbon dioxide (CO2). Diesel ships already use catalysts that treat nitrogen oxides alone. Ammonia ships need separate catalysts and extra equipment for the rest, which takes up space on board and raises installation costs. The team calls this the primary barrier to commercialization.

The team's hybrid catalyst removes nitrogen oxides and unburned ammonia together, with a single catalyst layer that decomposes both at about 99% efficiency. It is at least 80% less costly than existing noble-metal alternatives, and catalyst use can be reduced by up to 50%. The second catalyst targets nitrous oxide and operates at 350 °C, the actual temperature of ship exhaust and about 100 °C below conventional commercial catalysts, which the team says exceed 450 °C. It decomposes nitrous oxide with over 99% efficiency and needs no external reducing agent.

For a shipowner, the gain is in space, weight and money. The team says both catalysts can be integrated directly into existing exhaust treatment systems on diesel ships, which it expects to speed commercialization. That is an expectation, not a schedule: the next step is pilot-scale demonstrations on ammonia-fueled engine systems, and the team gives no date for them.

The figures come from the team's own catalytic reaction tests, published in Applied Catalysis B: Environment and Energy. They have yet to be checked on a running engine. Hwang calls the catalysts a breakthrough against "the most formidable barrier to ammonia-fueled shipping", a claim that will be tested once they leave the bench.