When atomic-scale resolution is not enough: Spatial effects on in situ model catalyst studies

► First-principles based multi-scale modeling. ► CO oxidation over RuO2(1 1 0) at ambient pressures. ► Mass-transfer effects may have a tremendous impact on model catalyst studies. ► Reactivity and surface composition vary along the catalyst surface in a channel. ► Stagnation flow shows mostly uniform composition and reactivity.