A review of multiscale modelling approaches for understanding catalytic ammonia synthesis and decomposition

Ammonia plays a crucial role in our lives as it is widely used, for example, in the synthesis of fertilizers, the production of carbon-free hydrogen for fuel cells, or electricity generation. However, the conventional Haber-Bosch process for ammonia synthesis has several drawbacks, such as requiring high temperatures and pressures, consuming 1-2% of the world's energy supply. While significant progress has been made in performing the reaction under milder conditions, the subject has experienced a second renaissance with the advent of multiscale modeling and improvements in computational capabilities. Multiscale modeling at various levels, including density functional theory (DFT), transition state theory (TST), kinetic Monte Carlo method (KMC), microkinetic modeling, molecular dynamics (MD), and computational fluid dynamics (CFD), allows us to describe the reaction system at all levels simultaneously. In this review, we focus on the treatment of ammonia synthesis, decomposition, or oxidation using multiscale models, ranging from the study of quantum-level interactions to the optimization of reactor design. Recently, significant progress has been made in modeling. Current modeling tools, while well developed, still have weaknesses in their linkage. DFT /TST is often coupled with KMC and MD or microkinetic data are fed into CFD while a comprehensive model is lacking. The potential for further progress through the use of multiscale models is enormous, which could lead to more efficient catalyst and process design.