Ammonia, a carbon-free resource can be split into nitrogen and hydrogen gas with the help of metal catalysts like Nickel (Ni). However, these reactions often require very high operating temperatures. Recently, scientists from Tokyo Institute of Technology (Tokyo Tech) have developed a calcium imide (CaNH)-supported Ni catalyst that can decompose ammonia at temperatures 100°C lower than what conventional Ni catalysts require. 

In a recent study published in ACS Catalysts, a team of researchers from Tokyo Tech led by Associate Professor Masaaki Kitano described a solution to overcome the issues faced by Ni-based catalysts. 

The team discovered that the presence of CaNH resulted in the formation of NH^2- vacancies (V_NH) on the surface of the catalyst. These active species resulted in the improved catalytic performance of the Ni/CaNH at reaction temperatures that were 100°C lower than those necessary for the functioning of Ni-based catalysts. The researchers also developed computational models and conducted isotope-labeling to understand what is happening on the catalyst surface. The calculations proposed a Mars−van Krevelen mechanism that involved adsorption of ammonia onto the CaNH surface, its activation at the NH^2- vacancy sites, formation of nitrogen and hydrogen gas, and finally regeneration of vacancy sites promoted by Ni nanoparticles.

"Our aim was to develop a highly active catalyst that would be energy efficient. Our addition of the metal imide to the catalyst system not only improved its catalytic activity but also helped us unravel the elusive working mechanism of such systems," said Kitano.

The highly active and durable Ni/CaNH catalyst can be successfully deployed for the generation of hydrogen gas from ammonia. Also, the insight into the mechanism of catalysis provided by this study can be utilized to develop a new generation of catalysts.