People are looking for cleaner options like hydrogen fuel because of the current global climate emergency and our quickly decreasing energy resources.
Hydrogen gas produces a lot of energy when burned in the presence of oxygen, but unlike fossil fuels, it doesn’t produce detrimental greenhouse gases. Unfortunately, the majority of today’s hydrogen is derived from natural gas or fossil fuels, which increases the carbon impact.
Because of its high energy density and hydrogen storage capacity, ammonia (NH3), a carbon-neutral hydrogen molecule, has gained a lot of attention recently. It has the ability to breakdown and release nitrogen and hydrogen. Ammonia is easily liquefied, stored, and transported, as well as transformed into hydrogen if necessary. The creation of hydrogen from ammonia, on the other hand, is a sluggish and energy-intensive process. Metal catalysts are frequently employed to speed up production while also lowering total energy usage in hydrogen synthesis.
Nickel (Ni) has recently been discovered to be a promising catalyst for ammonia splitting. Ammonia is adsorbed on the surface of Ni catalysts, where the ammonia’s nitrogen and hydrogen bonds are broken and the gases are liberated as separate gases. However, in order to accomplish good ammonia conversion using a Ni catalyst, very high operating temperatures are frequently necessary.
A team of Tokyo Tech researchers lead by Associate Professor Masaaki Kitano describes a strategy to address the issues of Ni-based catalysts in a study recently published in ACS Catalysis. They created a cutting-edge calcium imide (CaNH)-based Ni catalyst that allows for high ammonia conversion at low temperatures. Dr. Kitano elucidates: “Our goal was to create a highly active, energy-efficient catalyst. The addition of the metal imide to the catalyst system increased its catalytic activity while also assisting us in unraveling the enigmatic mechanism of such systems.”
The researchers noticed that the presence of CaNH caused NH2 vacancies ( VNH ) to form on the catalyst’s surface. These active species improved the Ni / CaNH catalyst’s catalytic performance at reaction temperatures 100 degrees Celsius lower than those required for Ni-based catalysts to function. To further understand what happens on the catalyst surface, the researchers created computational models and used isotope labeling. The calculations suggested a Mars-van Krevelen mechanism including ammonia adsorption on the CaNH surface, activation of the NH2 Vacancies, which includes the creation of nitrogen and hydrogen gas, and ultimately vacancy renewal by Ni nanoparticles.
The Ni / CaNH catalyst, which is extremely active and long-lasting, can be successfully employed to produce hydrogen gas from ammonia. The knowledge gathered in this study concerning catalysis mechanisms can be applied to the development of a new generation of catalysts. “As the entire globe works together to create a sustainable future,” Dr. Kitano says, “our study strives to overcome difficulties on the route to a cleaner hydrogen economy.”
