Interactions between adsorbates on surfaces are critical for many phenomena including promotion and poisoning in catalysis, nucleation and growth on surfaces. For example, alkali promoters (Li, Na, K, Rb, Cs) enhance activity and/or selectivity of various catalytic processes, such as Fisher-Tropsch synthesis, water-gas shift reactions, ammonia synthesis, olefin epoxidation, and automotive three way converters. Although the impact of alkalis in heterogeneous catalysis has been recognized for decades, not much is known about the underlying physical mechanisms that govern the promotion.

We have utilized density-functional theory (DFT) calculations to develop a simple and physically transparent model for the analysis of the interactions between adsorbates on metal surfaces. We have applied this model to investigate underlying mechanisms that govern the interaction between Cs promoters and oxygen adsorbates on Ag(111).

We have also employed an atomistic thermodynamics approach and ab initio Monte Carlo simulations to extend the results of DFT calculations to realistic temperature and pressure. We found that the underlying mechanisms of chemical promotion by alkali promoters change significantly as a function of external conditions.