The combination of surface science techniques with accurate quantum-mechanical numerical simulations applied to model catalytic systems like single-crystal samples under ultra-high vacuum conditions has allowed understanding and in selected cases predicting the catalytic behavior of materials, unveiling the contribution of surface structure, alloying, and coverage effects. Work is in progress nowadays to bridge to a certain extent the material and pressure gaps, dividing the single-crystal studies in vacuum typical of fundamental physics research and the investigation of catalysts under working (in situ and in operando) conditions. In this context and for the practical purpose of developing efficient catalysts, special attention is deserved nowadays to nanoparticles, due to their reactivity, surface to volume ratio, and peculiar behavior related to finite size effects. Furthermore, novel spectroscopic techniques that can be applied up to ambient pressure conditions and even in liquid and, in parallel, new algorithms for numerical simulations in realistic environments such as electrochemical cells are under development.
