The investigation of epitaxially grown, ultra-thin dielectric films on metal substrates is of great interest in the fields of catalysis and organic electronics. Here, we explore the energy alignment of adsorbates on top of dielectric/metal systems and their resulting charge state. Finally, we demonstrate the impact of charge transfer on fundamental physical and chemical. Organic and inorganic adsorbates are therefore systematically investigated on pristine silver single crystals (Ag(001)) and on Ag(001) supported magnesium oxide (MgO) ultra-thin films.We demonstrate integer charge transfer to the Lowest Unoccupied Molecular Orbital of pentacene (5A) adsorbed on MgO(001)/Ag(001) and fractional charge transfer of 0.7 electrons per molecule on pristine Ag(001). We identify the individual energy level alignment contributions and roughly quantify them. By varying the initial workfunction of the MgO(001)/Ag(001) substrate the equilibration mechanism, leading to the final, constant workfunction, is investigated.Charge transfer to 2-dimensional gold (Au) islands on MgO(001)/Ag(001) enables the catalytic formation of oxalates from carbon-dioxides. Here, we find a morphological transition from 2D to 3D Au-islands upon annealing to elevated temperatures that coincides with a significant decrease of the oxalate formation We conclude that the catalytic reactivity is facilitated by excess charges located on the rim of 2-dimensional Au-islands. In a related topic, we demonstrate that charge transfer controls the self-metalation reaction of free-base porphyrin (2H-TPP) to Mg-TPP on MgO(001)/Ag(001). We achieve this by tuning of the initial substrate workfunction, either enabling or inhibiting charge transfer, and monitoring of the N 1s XPS signal of the porphyrins. Furthermore, we present a scanning tunneling microscopy study on the monolayer formation of water on MgO(001)/Ag(001) and a combined-method growth study on Para-Sexiyphenyl (6P) on pristine Ag(001).