Haber-Bosch at the atomic scale

Industrial production of NH₃ has been performed by the Haber-Bosch process for more than 100 years, in which dissociation of N₂ feedstock molecules promoted by alkali atom co-catalyst is thought to be the rate limiting step. The Haber-Bosch synthesis consumes 1% of the world's total energy consumption, and accounts for 1.4% of the global CO₂ emissions. Therefore, the atomic scale insights into the K atom-N₂ molecule interactions on metal substrates and specifically, the alkali atom promotion chemistry, has global significance.

Researchers at the University of Pittsburgh, together with theoretical collaborators at the University of Science and Technology of China have investigated the Haber-Bosch catalysis precursor at the atomic scale.

In research article to be published in Cell Reports Physical Science on April 21, 2022, the researchers, led by Hrvoje Petek at the University of Pittsburgh, were able to directly observe at the atomic scale by scanning tunneling microscopy the N₂ adsorption, their collective interactions, and tunneling electron-induced N₂ desorption processes that are related to the alkali promotion of NH₃ synthesis.

The dominant pairwise interaction between the K and N₂ is an electrostatic, two-center, Coulomb attraction, where charge transfer from K to N₂ weakens the N₂ molecule bond towards its dissociation in the Haber-Bosch synthesis. The K-N₂ interactions interpreted through density functional theory are in agreement with the experimental observations.

The studies reveal the primary interactions, as well as the onset of correlated complexity that defines the alkali atom promotion of catalytic chemistry.