Ammonia (NH3) has been drawing attention as a carbon-free alternative fuel. NH3 could be widely used in thermal power generation and industrial furnaces as an alternative to gasoline and light oil. However, compared with fossil fuels, NH3 has a high ignition temperature; a low combustion rate and N2O/NOx production. To overcome these issues, the development of a novel NH3 combustion system would be required.
Now, researchers at the International Research Organization for Advanced Science and Technology (IROAST) at Kumamoto University, Japan, report a novel catalytic NH3 combustion system with copper oxide catalysts supported on aluminum silicates and silicon oxides for the combustion of ammonia. A paper on their work is published in the Journal of Catalysis.
|CuOx/3A2S selectively produces N2 and H2O from NH3 through a two-step reaction. Credit: Dr. Satoshi Hinokuma. Click to enlarge.|
… catalytic combustion … is regarded as a promising technique for decreasing emissions from hydrocarbon-based fuels and was actively studied for use in gas turbines, boilers, and jet engines in the 1980s. This system has many advantages over conventional noncatalytic combustion, as NOx emission is greatly diminished by the low operating temperatures and high efficiency can be achieved through stable combustion.
More recently, RenCat (a start-up company in Denmark) has been commercializing technology to decompose NH3 into H2 for use in fuel cells. … NH3 decomposition (cracking) reaction is endothermic, whereas NH3 combustion reaction is exothermic. Therefore, … NH3 decomposition can be effectively promoted by the heat produced from NH3 combustion.
Therefore, to establish the further potentiality of NH3 fuel, it is desirable to develop a novel catalyst with high thermal stability that enables the use of low ignition temperatures while resulting in negligible N2O/NOx emission.—Hinokuma et al.
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—i.e., 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 NH3 fuel combustion, and the purification of NH3 through oxidation.
Study leader Dr. Satoshi Hinokuma of IROAST said that the team plans to conduct further research and development under more practical conditions in the future.
Satoshi Hinokuma, Saaya Kiritoshi, Yusuke Kawabata, Kento Araki, Shun Matsuki, Tetsuya Sato, Masato Machida (2018) “Catalytic ammonia combustion properties and operando characterization of copper oxides supported on aluminum silicates and silicon oxides” Journal of Catalysis Volume 361, Pages 267-277 doi: 10.1016/j.jcat.2018.03.008