The role of the N₂/H₂ reactant gas mixture on nitrogen activation in the Haber-Bosch process

Much effort has been devoted to the study of the Haber-Bosch catalytic process. However, one aspect that has not yet been investigated is the role of the presence in front of the catalytic surface of a dense hot gaseous mixture of N₂ and H₂. Here, we develop a grand-canonical simulation method that, together with machine-learning-generated reactive potentials, enables the simulations of such gas/substrate interface. At the operando conditions of pressures above 150 bar and temperatures higher than 700 K, H₂ molecules dissociate upon impinging on the (110) iron surface. The resulting adsorbed atoms diffuse, recombine, and exchange with the gas phase, establishing a dynamical equilibrium that leads to substantial coverage, which nevertheless remains below saturation. We investigate the dissociative adsorption of N₂ on Fe(110), from a stoichiometric N₂:H₂ gas mixture. Our simulations reveal a catalytically active surface despite the high coverage, suggesting that under realistic industrial conditions the hydrogen-rich surface modulates the elementary steps of the process.