Preparation of exfoliated zeolites from layered precursors: The role of pH and nature of intercalating media

摘要

The ability to modify interlayer separation and arrangements in lamellar solids by appropriate chemical treatment has been exploited to generate novel porous materials. Treatments such as intercalation or delamination may be quite demanding and sensitive to various factors. This is illustrated by the zeolitic layered material, MCM-22 precursor, which can be swollen with a cationic surfactant but requires a high pH environment. The resulting product, swollen MCM-22 precursor, may then be converted to the pillared mesoporous material, MCM-36, or to a delaminated solid with randomly oriented layers. This report deals with the issues associated with swelling of the layered MCM-22 precursor, which is the critical step. We focus on the problem of swelling efficiency when the required surfactant medium with high pH is a mixture of a base (NaOH or tetraalkylammonium hydroxide) and cationic surfactant chloride. Only the combination with tetrapropylammonium hydroxide produced swelling, while the methyl and ethyl homologues did not. This indicates dependence on the nature of cations present in the swelling medium. We also discuss in detail the criteria for identification and quantification of the swollen product and avoidance of potential impurities.