Title : Catalytic hydrogen production: Unlocking ammonia as a hydrogen carrier
Abstract:
As a clean energy carrier with high gravimetric energy density, hydrogen is expected to find various applications in fuel cell systems and other renewable energy technologies. Nevertheless, large-scale hydrogen utilization still faces many obstacles related to its production, storage, transportation, and safe handling. Traditionally, hydrogen has been stored using high-pressure compression or cryogenic liquefaction, leading to higher energy costs, complex technological processes, and higher cost. Thus, significant efforts have been devoted to developing hydrogen rich chemical hydrogen carriers that could provide effective hydrogen storage and generation. Ammonia (NH?) is one of the hydrogen carriers with a high hydrogen content (17.6 wt%), well established facilities for production and transportation and convenient storage conditions relative to hydrogen. The most important advantage is that ammonia can be converted into hydrogen via catalytic decomposition (2NH? → N? + 3H?) with no direct CO? emissions and thus can be used as the feedstock for on-site hydrogen generation. The key requirement for ammonia decomposition is highly active and stable catalysts providing high conversion rate at low reaction temperatures. In several studies performed on different catalysts used for the ammonia decomposition reaction, ruthenium (Ru) catalysts have shown outstanding catalytic activity. The efficiency of Ruthenium (Ru), however, is highly dependent on physicochemical characteristics of the support such as the surface area, metal-support interactions, electronic characteristics, dispersion of active Ru, and surface basicity. CeO2 is one of the effective supports due to its unusual redox properties, oxygen storage capability, and interaction capability with the metal on the support. The major downside of CeO2, however, is its high price that limits its wide usage as a bulk support. In the present study, catalytic decomposition of ammonia was explored for the generation of CO2-free hydrogen using Ru catalysts. In order to minimize the usage of CeO2 while keeping its advantages in catalysis intact, a core-shell type support configuration was adopted in which CeO2 was used to modify metal oxide supports. Ru catalysts were prepared using such modified metal oxide supports. It was observed that the composition and nature of the support played an important role in the activity of ammonia decomposition. The prepared core-shell supported Ru catalysts showed good hydrogen yield. It is evident that the use of CeO2 strategically allows the benefit of its promotion without using it as the main support material. Therefore, these prepared catalysts were suggested as cost-effective efficient catalysts.
