Advances in the Design of Pillared Clay Catalysts by Surfactant and Polymer Modification

Abstract

ABSTRACTThe catalytic properties of pillared clays for organic chemical conversions, especially those occurring in liquid media, can be substantially improved by surfactant modification of the pore structure during the pillaring reaction. For instance, the incorporation of a non-ionic surfactant, such as the alkylated polyethylene oxide C12–14H25–29O(CH2CH2O)5H, in the synthesis of alumina pillared montmorillonite results in a dramatic increase in the interparticle (textural) mesoporosity of the final calcined products. These surfactant-modified mesoporous pillared clays are exceptionally active as catalysts for the diffusion controlled liquid phase alkylation of biphenyl. The enhanced mesoporosity facilitates access of the reactants to the active acid sites in the interlayer nanopores of the pillared clay tactoids. Organic polymeric molecules also can be used to mediate the pore structure of pillared clay materials. The reaction of aluminum chlorohydrate oligomers with Na+ rectorite in the presence of polyvinyl alcohol as a pillaring precursor affords a supergallery alumina pillared rectorite with a basal spacings of 52 Å and a corresponding gallery height of 33 Å under air- dried conditions. A stable gallery height of 23 Å is observed even after treatment with 100% steam at 800°C for 17 hour. The new supergallery intercalate is characterized by a surface area, pore volume, and catalytic cracking activity superior to conventional alumina pillared rectorite and related smectites with 9 Å gallery heights.