Scientists from Great Britain were faced with a mysterious phenomenon: the catalyst they proposed for producing hydrogen from ammonia behaved in an inexplicable way. Typically, catalysts reduce their activity during operation, but the new one, on the contrary, became more and more efficient. This forced researchers to study the atomic structure of the substance, which, by all indications, violated the laws of physics.
Image source: University of Nottingham
Ammonia is considered one of the most energy-intensive carriers. However, to use it directly, it must be decomposed into hydrogen (H₂) and nitrogen (N₂). The reaction occurs most efficiently in the presence of a catalyst, such as ruthenium (Ru), which is a rare earth element. Researchers from the Department of Chemistry at the University of Nottingham, in collaboration with the University of Birmingham and Cardiff University, have developed a catalyst based on a graphite rod with nanometer-sized inclusions of ruthenium. Ruthenium nanoclusters came into contact with ammonia and decomposed it into hydrogen and nitrogen. Surprisingly, the longer the catalyst worked, the higher its activity became – the reaction accelerated.
«We were surprised to find that the activity of ruthenium nanoclusters in carbon actually increases with time, which is contrary to the deactivation processes that typically occur with catalysts during their use. This exciting discovery cannot be explained by traditional analytical methods, so we developed a microscopic approach to count the atoms in each catalyst nanocluster at different stages of the reaction using scanning transmission electron microscopy. We identified a series of subtle but significant changes at the atomic level,” said Dr. Yifan Chen, a research fellow in the Department of Chemistry.
The catalyst elements were made by magnetron sputtering, in which plasma in magnetic fields sputters a target (in this case, ruthenium) and deposits the material onto a carrier (graphite rod). This method ensures that most of the catalyst atoms are located on the surface of the support, where they can interact with the feedstock, rather than remaining deep inside the material.
A study of the atomic structure of the catalyst showed that during operation, ruthenium spontaneously assembles into nanoclusters with an area of 2–3 nm². These nanoclusters form stepped truncated pyramids. In this form, the catalyst gradually increases the active surface area, which explains its increasing efficiency.
«This discovery sets a new direction in catalyst development, demonstrating a stable, self-improving system for producing hydrogen from ammonia as a clean energy source. We expect that this breakthrough will make a significant contribution to the development of sustainable energy technologies, supporting the transition to a zero-carbon future,” summed up Andrey Khlobystov, professor at the Faculty of Chemistry.