Kumamoto University researchers have succeeded in developing a new catalyst that burns NH3 at a low temperature and produces N2. The results are expected to offer a carbon free fuel and increased renewable energy use.

Schematic of the newly developed catalyst and NH3 combustion reaction. CuOx/3A2S selectively produces N2 and H2O from NH3 through a two step reaction. Image Credit: Dr. Satoshi Hinokuma, Kumamoto University. Click image for the largest view.

Ammonia (NH3) has attracted attention in recent years as a carbon-free fuel that does not emit carbon dioxide. For use as a fuel, it should have a lower combustion temperature and produce only nitrogen (N2) and water.

Coming up with significant amounts of renewable fuel for power is one of the most important issues common to developed countries today. One promising technology in those efforts uses hydrogen (H2) as a renewable energy source. Although it is a primary candidate for clean secondary energy, large amounts of H2 would ideally be converted into liquid form, which is a difficult process, for easier storage and transportation.

Among the possible forms of liquid H2, ammonia (NH3) is a promising carrier because it has high H2 density, is easily liquefied, and can be produced on a large-scale.

NH3 is a combustible gas that can be widely used in thermal power generation and industrial furnaces as an alternative to gasoline and light oil. However, it is difficult to burn because of its high ignition temperature and it generates nitrogen oxides (NOx) during combustion.

Researchers at the International Research Organization for Advanced Science and Technology (IROAST) in Kumamoto University, Japan focused on a “catalytic combustion method” to solve the NH3 fuel problems.

This method adds substances that promote or suppress chemical reactions during fuel combustion. Recently, they succeeded in developing a new catalyst which improves NH3 combustibility and suppresses the generation of NOx.  The team’s research paper has been published in Journal of Catalysis.

The novel catalyst (CuOx/3A2S) is a mullite-type crystal structure 3Al2O3·2SiO2 (3A2S) carrying copper oxide (CuOx). When NH3 was burned with this catalyst, researchers found that it stayed highly active in the selective production of N2, meaning that it suppressed NOx formation, and the catalyst itself did not change even at high temperatures. Additionally, they succeeded with in situ (Operando) observations during the CuOx/3A2S reaction, and clarified the NH3 catalytic combustion reaction mechanism.

Since 3A2S is a commercially available material and CuOx can be produced by a method widely used in industry (wet impregnation method), this new catalyst can be manufactured easily and at low cost. Its use allows for the decomposition of NH3 into H2 with the heat from (low ignition temperature) NH3 fuel combustion, and the purification of NH3 through oxidation.

Study leader Dr. Satoshi Hinokuma of IROAST said, “Our catalyst appears to be a step in the right direction to fight anthropogenic climate change since it does not emit greenhouse gasses like CO2 and should improve the sophistication of renewable energy within our society. We are planning to conduct further research and development under more practical conditions in the future.”

NH3 rather neatly solves the hydrogen storage matter. For now the source for the hydrogen in ammonia production is natural gas with a (usually) side production of dry ice or frozen carbon dioxide. There are getting to be a lot of methods to come up with the hydrogen, and the N2 is free from the atmosphere.

NH3 isn’t a nirvana answer. Its a very strong base and is gaseous at ambient temperatures and pressures. Its still a different kind of dangerous compared to gasoline. There is already a lot of it around unnoticed and once in long while someone will have a mishap and get an alkali burn which is very different than an incinerating kind of fire.

Still, NH3 is a high potential, practical, long term storage solution for a hydrogen fuel resource.


1 Comment so far

  1. Jagdish on May 1, 2018 7:10 PM

    Production of hydrogen is an energy sinkhole. Ammonia use is best kept to present ones.
    Liquid fuels are best produced either by more efficient use of solar power or nuclear power. Short chain, non-smoking CHO compounds will remain the best. Natural or industrial carbon fixation is the best.

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