Confinements effects in MCM-41-type materials: Comparison of the energetics of n-hexane and 1-hexene adsorption

n-Hexane and 1-hexene adsorption on mesoporous silicas from the vapour phase has been studied in the temperature range 260 K up to 350 K. Classical models for the textural characterization of MCM-41 have been employed and converged with nitrogen adsorption results. These systems were found to weakly interact with silica surface, especially in the case of n-hexane, which is demonstrated both by low CBET values and extrapolation at zero coverage of isosteric enthalpies of adsorption which do not depend on pore size. Values ranging between −37 and −43 kJ mol−1 for n-hexane and −47 up to −55 kJ mol−1 for 1-hexene were found. On the other hand, latent enthalpies of condensation in the mesopores were found strongly pore size dependent suggesting that liquid fluids in small mesopores undergo confinement effects. Large enthalpic excesses were observed (up to 12 kJ per mole of condensing adsorbate) and a macroscopic model based on scaling effects has been employed to explain those results.