Cation Size Effects in Swelling of the Layered Zeolite Precursor MCM-22-P

The chemistry and apparent cation size effects associated with swelling of the layered precursor of zeolite MCM-22 are discussed in detail and rationalized. The swelling is achieved with a custom made solution, hexadecyltrimethylammonium hydroxide (CTMA-OH) due to combination of high pH and adsorption of the cation on the surface. Alternative swelling mixtures comprising surfactant chloride (CTMA-C1) and another base, i.e. Na or tetraalkylammonium hydroxide (alkyl = methyl, ethyl, propyl) have been tried. Swelling occurred only with the tetrapropylammonium base indicating competition between CTMA and the accompanying cation. Tetrapropylammonium cation (TPA) size appeared greater (i.e. ∼ 9 A in diameter) than the spacing between silanol groups (8.2 A) on the surface, which made it less effective in competition with the surfactant cations for electrostatic attachment to the surface.