Pure-Silica Zeolite MFI Crystals with Organic-Modified Interiors

Zeolites with organic-modified interiors can significantly widen the range of the applications of molecular sieving materials in separations, catalysis and other areas. Internal surface functionalization of zeolites can be accomplished by covalently binding organic groups to silanols or other reactive sites in the internal pore structure. The functionalized zeolite would then become an organic-inorganic hybrid with a potential for a diverse range of new applications. In this presentation, we describe the functionalization of pure-silica MFI zeolite crystals with selected functional groups that confer different types of chemical functionality to the zeolitic material. Detailed characterization by a number of techniques including NMR, TGA/DSC, and N₂ physisorption suggests that these functional groups are chemically bound to the internal pore sites and that the functional group loading is strongly dependent on the concentration of internal silanol defects. We then discuss the gas adsorption behavior of the functionalized materials, and show that their adsorption properties are significantly different from those of bare MFI zeolite materials. These results are explained in terms of the specific interactions between the organic-modified zeolite material and the gas molecules of interest.