LAUSR

This review explores the catalytic decomposition of ammonia into hydrogen, a critical process for sustainable hydrogen production. As ammonia rapidly emerges as the preferred carrier for hydrogen storage and transport, efficient decomposition methods are crucial for advancing hydrogen's role in the energy transition. While previously published reviews have primarily focused on metal catalysts such as Ru, Ni, and Co, as well as the influence of supports and other catalytic systems, recent developments in transitioning from nanoparticles to single-atom and cluster catalysts (SACs) have not been extensively covered. Here, we provide a comprehensive analysis of recent advances in the development of nanoparticle, SAC, and metal cluster catalysts-including noble metals, transition metals, and bimetallic systems-for ammonia cracking and their structure-activity relationships. In particular, ruthenium (Ru) remains the standout catalyst due to its exceptional activity and stability. Additionally, it was found that SACs, and metal clusters exhibit remarkable catalytic performance due to their high atom utilization and distinct electronic properties compared to traditional nanoparticle catalysts. This review also discusses the challenges and future opportunities in the field, highlighting the potential of metal catalysts, SACs, and metal clusters to revolutionize ammonia cracking and hydrogen production technologies.