STUDY OF THE MOLECULAR ELECTROSTATIC POTENTIALS OF ZEOLITES - THE ACIDITY IN OFFRETITE

The work covers specific acidic properties of offretite. These properties have been chosen as a trial of the presently used theoretical model, based on molecular electrostatic potentials (MEP) calculated with extended Hueckel wave functions. In the first part of this study, it is shown that these MEPs are in good agreement with MEPs calculated with ab initio wave functions. In the second part, the analysis of the MEP wells near the oxygen sites of the electrophilic attack by a proton shows that an aluminated T//2 site enhances the acidity of the zeolite, with respect to an aluminated T//1 site. Moreover, the analysis of the extended Hueckel results indicates that the less acidic sites are the most easily dealuminated. These conclusions are in complete agreement with the experimental findings.