Hydrogen Economy Core Ammonia... Development of Low-Temperature, Low-Pressure Synthesis Catalyst

Hydrogen production using renewable energy is a key technology for eco-friendly energy and chemical production. Produced hydrogen is difficult to store and transport. Research is being conducted worldwide to store hydrogen in the form of ammonia (NH3), which does not emit carbon and is easy to liquefy.



A research team at the Korea Advanced Institute of Science and Technology (KAIST) has developed a high-performance catalyst that can synthesize ammonia without energy loss even at very low temperatures and pressures.



KAIST (President Lee Kwang-hyung) announced on the 11th that Professor Choi Min-ki's research team in the Department of Chemical and Biomolecular Engineering has developed an innovative catalyst system that can dramatically increase ammonia productivity while significantly reducing energy consumption and carbon dioxide emissions. Schematic diagram



showing the mechanism of ruthenium catalyst activity enhancement by barium oxide promoter. [Photo = KAIST]



Currently, ammonia is produced using iron (Fe)-based catalysts using the Haber-Bosch process, a technology that is over 100 years old. This method requires high temperatures of over 500℃ and high pressures of over 100 atm, consuming enormous amounts of energy. It



has been identified as the main culprit that accounts for a significant portion of global carbon dioxide emissions. Moreover, since ammonia produced in this way is manufactured in large factories, distribution costs are not insignificant.



As an alternative, interest in an eco-friendly process that synthesizes ammonia at low temperature and low pressure (300 degrees, 10 atm) using green hydrogen produced through water electrolysis, a technology that decomposes water using electricity, is rapidly increasing.



To implement this process, it is essential to develop a catalyst that can secure high ammonia productivity even at low temperatures and pressures. With current technology, ammonia productivity is low under these conditions, so overcoming this remains a key challenge.



The research team developed a new concept catalyst that operates like a 'chemical capacitor' by introducing a ruthenium (Ru) catalyst and barium oxide (BaO) particles with strong basicity to a highly conductive carbon surface.



During the ammonia synthesis reaction, hydrogen molecules (H2) are decomposed into hydrogen atoms (H) on the ruthenium catalyst. These hydrogen atoms are decomposed once more into pairs of protons (H+) and electrons (e-).



It was found that acidic protons are stored in strongly basic barium oxide, and the remaining electrons are separated and stored in ruthenium and carbon. It was found that



the ruthenium catalyst, which is enriched in electrons through this unique chemical storage phenomenon, dramatically enhances catalytic activity by promoting the decomposition process of nitrogen (N2) molecules, which are key to the ammonia synthesis reaction.



In this study, it was discovered that the electron density of ruthenium can be maximized by controlling the nanostructure of carbon, thereby enhancing catalytic activity. This catalyst showed an ammonia synthesis performance that was more than 7 times higher than that of the existing best catalysts under mild conditions of 300 degrees and 10 atm.



Professor Choi Min-ki said, "This study is receiving great attention from the academic world because it shows that catalytic activity can be greatly enhanced by controlling the electron transfer inside the catalyst even in general thermochemical catalytic reaction processes, not electrochemical ones."



He continued, "At the same time, through this study, we confirmed that efficient ammonia synthesis is possible even under low-temperature and low-pressure conditions by utilizing a high-performance catalyst." He continued, "This will enable distributed, small-scale ammonia production that moves away from the existing large-scale, factory-centered production method, and is expected to enable more flexible ammonia production and utilization suitable for an eco-friendly hydrogen economy system."



The research results (paper title: Electron and proton storage on separate Ru and BaO domains mediated by conductive low-work-function carbon to accelerate ammonia synthesis) in which Professor Min-ki Choi of the Department of Chemical and Biomolecular Engineering participated as the corresponding author and PhD student Ye-jun Baek as the first author, were published in the international academic journal in the field of catalysis and chemistry, Nature Catalysis, on February 24.





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