MODIFICATION OF ZEOLITIC MICROPOROSITY WITH TAILORED SURFACE-PROPERTIES

The microporosity of zeolite H-mordenite has been modified by incorpor ation with silicon modifying groups derived from chemisorption of disi lane. The modifying group, occupying more than 110 Angstrom(3) in the main channel, progressively reduces the pore size of the zeolite with precision that can be less than 1 Angstrom. This is indicated by conti nuous exclusion of gradually smaller molecules (p-xylene, propane, eth ane, and methane) from the sorption. As the modification degree is fur ther increased, the side pockets of H-mordenite become blocked and are inaccessible to nitrogen and oxygen. Substantial changes in sorption selectivities of oxygen versus nitrogen have also been observed on the modified zeolite after the protons in the main channels have been rep laced by the silicon entities. A study of the thermodynamic properties and the contributions of sorption energy has revealed, for the first time, that such changes in molecular selectivities are directly relate d to the interplay of the pore size and the polarity of the substrate controlled by the modification process.