Non-linear temperature dependence of nitrogen adsorption and decomposition on Fe(111) surface

The cleavage of the N2 triple bond on the Fe(111) surface is believed to be the rate limiting step of the famed Haber-Bosch ammonia catalysis. Using a combination of machine learning potentials and advanced simulation techniques, we study this important catalytic step as a function of temperature. We find that at low temperatures our results agree with the well-established picture. However, if we increase the temperature to reach operando conditions the surface undergoes a global dynamical change and the step structure of the Fe(111) surface is destroyed. The catalytic sites, traditionally associated with the Fe(111) surface appear and disappear continuously. Our simulations illuminate the danger of extrapolating low-temperature results to operando conditions and indicate that the catalytic activity can only be inferred from calculations that take dynamics fully into account. More than that, they show that it is the transition to this highly fluctuating interfacial environment that drives the catalytic process.