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.

Dynamics has long been recognized to play an important role in heterogeneous catalytic processes. However, until recently, it has been impossible to study their dynamical behavior at industry-relevant temperatures. Using a combination of machine learning potentials and advanced simulation techniques, we investigate the cleavage of the N 2 triple bond on the Fe(111) surface. 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 destabilized. The catalytic sites, traditionally associated with this 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.

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.

Despite the Haber-Bosch process being more than 100 years old, only incremental improvements have been achieved until recently. Now, by combining the catalyst expertise of CLARIANT and the engineering knowledge of CASALE, a breakthrough has been realized. AmoMax®-Casale is a new ammonia synthesis catalyst jointly developed by Casale and Clariant particularly for use in Casale ammonia converters. AmoMax®-Casale is a customized evolution of the well-known, wustite-based catalyst, AmoMax® 10. While retaining the same superior resistance to ageing, poisoning and mechanical strength, AmoMax®-Casale is significantly more active. This feature allows to reduce the loop recycle rate and the loop pressure and/or to increase the ammonia production. The higher activity of AmoMax®-Casale contributes to improve the overall operating efficiency either by saving energy, or by increasing significantly the plant capacity. This article will describe in detail the successful development of AmoMax®-Casale, explain advantages and commercial benefits based on concrete plant simulations and share the start-up experience of the first commercial reference.

Ammonia synthesis remains one of the most important catalytic processes since it enables efficient hydrogen storage and provides the basis for the production of fertilizers. Herein, complementary bulk and local analytical techniques were combined to investigate the effect of selected promoters (Al, K, Ca) on the reduction of wuestite into alpha-iron and their catalytic performance for ammonia synthesis. The use of promoters appears to have a positive effect on the wuestite-derived catalyst in ammonia synthesis. The promoters seemingly act as a binder for wuestite grains and impede the reduction and disproportionation events of wuestite precursors resulting in an increased catalytic performance. This effect is associated with an increase of surface area and mesoporosity. The study delivers new insights into the interplay of structure and promoters in wuestite-based catalysts.

Tradition is tradition: Already for the 52(nd) time the Annual Meeting of the German Catalysis Society (GeCatS) took place from March 13th to 15th, 2019. Following its long-standing tradition, the meeting was organized in the Neue Weimarhalle in the beautiful city of Weimar, Thuringia.