Turning the heat down: Catalymon formation of ammonia at lower temperatures with ruthenium

Nitrogen is an essential nutrient for plant growth. Although about 80% of soil is nitrogen, it is mostly in the atmosphere as a gas, so it is not accessible to plants. To stimulate plant growth, especially in agricultural conditions, therefore, nitrogen chemical fertilizers are required. A crucial step in the production of these fertilizers is the synthesis of ammonia, which involves the reaction between hydrogen and nitrogen in the presence of catalpa.

Traditionally, ammonia production has been carried out through the “Haber-Bosch” process, which, despite being efficient, requires high temperature conditions (400-500 ° C), making the process expensive. . As a result, scientists have been trying to find a way to reduce the reaction temperature of ammonia synthesis.

Recently, scientists have reported that ruthenium – a transition metal – is an effective “catalyst” for ammonia synthesis, as it works under milder conditions than traditional iron-based catalysts. However, there is a caveat: nitrogen molecules must adhere to the surface of the catalyst to pass through separation into atoms before reacting with hydrogen to form ammonia. For ruthenium, however, the low temperature often causes hydrogen molecules to adhere to its surface – a process known as hydrogen poisoning – which inhibits ammonia production. To work with ruthenium, therefore, hydrogen poisoning must be eliminated.

Fortunately, some substances can increase the catalytic activity of ruthenium when used as a “catalpa support.” A team of scientists from Tokyo Tech, Japan, recently revealed that lanthanide hydride products of the form LnH2 + x are one group of such auxiliary materials. “The improved catalytic performance is achieved by two specific properties of the supporting material. First, they provide electricity, which directs the separation of nitrogen on the surface of ruthenium. Second, these electrons ‘combines with hydrogen on the surface to form hydride ions, which readily react with nitrogen to form ammonia and release the electrons, eliminating the hydrogen poisoning of ruthenium “, explains the Professional Professor Maasaki Kitano, who led the study.

With suspicion that ion hydride movement may play a role in ammonia synthesis, the team, in a new study published in Advanced Energy Products, studied the performance of lanthanide oxyhydrides (LaH3-2xOx) – reportedly fast ion hydride conductors at 100-400 ° C – as a support material for ruthenium, with the aim of finding out the relationship between ammonia synthesis and ion transfer hydride.

They found that although the “major” ion hydride behavior had little effect on ammonia synthesis activity, surface or local movement of “hydride ions” played a crucial role in catalysis by helping to build immunity. strong against ruthenium hydrogen poisoning. They also found that, compared to other adjuvants, lanthanum oxyhydrides required lower starting temperatures for ammonia formation (160 ° C) and showed higher catalytic activity.

In addition, the team found that the presence of oxygen stabilized the oxyhydride framework and the hydride ions against nitridation – the transformation of lanthanum oxyhydride to lanthanum nitride and its subsequent degradation – which tends to inhibit catalysis and which is a major attraction in the use of hydride support materials. “Resistance to nitridation is a major advantage as it helps maintain the electron donation potential of hydride ions for a longer period of reactivation,” said Drs. Kitano.

So perhaps the improved catalytic performance and lower synthesis starting temperature achieved by using lanthanide oxyhydrides is the solution that is in great demand for converting the heat down to ammonia production!

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