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

摘要

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 8)on the surface,which made it less effective in competition with the surfactant cations for electrostatic attachment to the surface.