In this Thesis, we have studied the adsorption on oxides and metals by means of Density Functional Theory simulations plus a semiempirical correction for dispersion. First we have investigated rutiles, which have the same unit cell and can be mixed with new properties. When impurities are present, semi conductors are found on the surface and metallic compounds in the bulk and oxygen reverse this behaviour. Also, we can epitaxially grow any rutile on top of another. Next we have addressed the adsorption of alcohols on Titania. Our results indicate that both the energies and the geometries of adsorption are not scalable with the chain length and the number of hydroxyls. This warns against the use of small alcohols as surrogates. Afterwards, the conversion of ethylene glycol and 1,3-propanediol to alkenes on TiO2 has been analyzed. The former evolves easily to the products while the latter pass through a high energy intermediate. The process is not catalytic, since a vacancy is healed after each cycle. To assess the e_ect of the water environment, we have investigated the hydrophobicity of Rare-Earth Oxides. The reason behind this property is the particular water arrangement which is related to the distance between the surface ions. We altered such motif doping the surface thus modifying the mean distance between the ions. Finally, we developed new parameters for dispersion corrections in metals from the computed polarizability. The procedure is first principles and can be employed in defective surfaces.