Ammonia has recently emerged as a liquid storage and transport medium that has shown promising stability for long-distance hydrogen transport. At 108 kg H2/m3, liquefied ammonia (NH3) can store 50% more hydrogen than liquid hydrogen. When ammonia is decomposed at high temperatures, only hydrogen and nitrogen gases are produced, with minimal carbon dioxide emissions.
Because more than 200 million tons of ammonia are currently produced annually for industrial use around the globe, the infrastructure for its mass storage and long-distance transport already exists and could simply be re-purposed for hydrogen transport. However, the need for large amounts of heat has thwarted the widespread adoption of ammonia for use in hydrogen transport and storage.
The decomposition reaction through which hydrogen is extracted from ammonia can only proceed at high temperature—which requires high energy input. A catalyst in the form of a solid powder can be added during the decomposition reaction to lower the reaction temperature; however, the existing ruthenium-metal-based catalysts are very expensive and have low stability, thus requiring regular replacement.
Now, researchers at the Korea Institute of Science and Technology (KIST) led by Drs. Hyuntae Sohn and Changwon Yoon have developed a catalyst for hydrogen production from ammonia decomposition that exhibits 2.5-times higher ammonia decomposition performance than conventional commercial catalysts. The results of this study were published in the journal Applied Catalysis B: Environmental.
The catalyst consists of ruthenium metal particles and zeolite strongly bound by calcination under vacuum, resulting in the containment of sub-nanometer and nanometer ruthenium metal particles in each pore of the zeolite support.
A schematic diagram of the catalytic structure for ammonia decomposition developed by KIST researchers. Credit: Korea Institute of Science and Technology (KIST)
This novel catalyst achieves its efficiency while using only 40% of ruthenium metal compared to existing catalysts. Because nanometer-sized (or smaller) ruthenium metal particles are present and maintain their stability during the ammonia decomposition process even at high reaction temperatures, the use of the proposed catalyst can overcome the problem of low stability, which has been significantly limiting the commercialization of existing catalysts.
The developed catalyst has an advantageous structure in that the nanometer-sized ruthenium metal particles are uniformly spread over zeolite, a crystalline mineral. Thus, this catalyst has shown higher performance and stability than previously reported catalysts and is expected to facilitate the commercialization of the process for high-purity hydrogen production from ammonia.—Dr. Hyuntae Sohn
The importance of large-capacity hydrogen transport based on ammonia is rapidly increasing, with fierce competition among advanced countries over the development and acquisition of related technologies. The application of the proposed catalyst for large-capacity hydrogen production via ammonia decomposition, which is currently under research and development, will ultimately help the commercialization of ammonia-derived hydrogen and the large-capacity hydrogen transportation between countries.—Dr. Changwon Yoon
This research was supported by the New & Renewable Energy Core Technology Program of the Korea Institute of Energy Technology Evaluation and Planning(KETEP), granted financial resources by the Ministry of Trade, Industry & Energy (MOTIE).
Junyoung Cha, Taeho Lee, Yu-Jin Lee, Hyangsoo Jeong, Young Suk Jo, Yongmin Kim, Suk Woo Nam, Jonghee Han, Ki Bong Lee, Chang Won Yoon, Hyuntae Sohn (2021) “Highly monodisperse sub-nanometer and nanometer Ru particles confined in alkali-exchanged zeolite Y for ammonia decomposition,” Applied Catalysis B: Environmental, Volume 283 doi: 10.1016/j.apcatb.2020.119627