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.