Lokale wechselwirkungen bei der sorption von aromaten in ZSM 5-zeolithen

The energetic and entropic contributions in the sorption of benzene in H/ZSM 5 were studied. The sorption of benzene in the pores was determined primarily from the non specific exchange effect with the pore walls while the localized exchange effects of benzene with the bridged hydroxyl groups played a subordinate role energetically. Through the sorption of benzene at the hydroxyl groups the frequency of the stretch oscillation shifted to lower wave numbers and the characteristic IR bands for OH groups was observed that exchanged in the form of hydrogen bridge bonding with the aromatic molecules. Through the description of the isotherms with a Langmuir expression the equilibrium constants were determined as a function of the temperature and thereby the entropic and enthalpic contributions of the sorption were determined. The measurements indicated that benzene sorbed in two orientations in the pores differentiated by the steric environment.