Mixed metal oxides in catalytic ammonia cracking process for green hydrogen production: A review

Hydrogen, a versatile energy carrier, is a promising alternative to replace the environmentally harmful and unsustainable use of fossil fuels. This much-touted fuel of the future may however have pitfalls, such as issues associated with hydrogen production, storage, and distribution. Hydrogen storage and distribution are concerned with various technical, environmental and safety issues. Indirect hydrogen storage methods such as – in solid-state materials, ammonia, and methanol/ethanol – are recently being considered by academic and industry parties. Ammonia (NH3) can be a promising carbon-free carrier with a high energy density, established transportation network, high hydrogen contents and high flexibility. Hydrogen production from NH3 decomposition requires catalyst/support such as metal oxides. In binary metal oxides like perovskites and spinels, their unique morphologies and structural flexibility enable to apply defined control over the reaction profile through detailed engineering material design. The focus of this study is to conduct a comprehensive review on the existing and emerging mixed metal oxides catalysts used in the NH3 decomposition process in hydrogen production. The activity of various mixed metal oxide catalysts is critically assessed, and their resulting performances are discussed in detail. Furthermore, this study covers challenges associated with hydrogen production through the catalytic NH3 cracking process.