Sol-gel synthesis and pillaring reactions of beidellite and related smectite layered silicates

The 2:1 relation between the tetrahedral and octahedral sheets of smectite clays allows these minerals to be classified as a 2:1 phyllosilicate. Smectites are readily pillared owing to the combination of swelling ability, low charge density and transverse layer rigidity. Beidellite is a member of the smectite family of 2:1 layered silicate clays, in which the net negative charges on oxygen framework arise mainly from the substitution of Al{dollar}{bsol}sp{lcub}3+{rcub}{dollar} for Si{dollar}{bsol}sp{lcub}4+{rcub}{dollar} in the tetrahedral sites. This structural analogy to zeolite makes this clay and its aluminum pillared derivatives more attractive for acid catalytic application relative to montmorillonite and other smectites in which the layer charge arises from metal ion substitution on the octahedral sheet. In the present work well-crystallized beidellite is synthesized at 200{dollar}{bsol}sp{bsol}circ{dollar}C, whereas conventional synthesis temperature is over 300{dollar}{bsol}sp{bsol}circ{dollar}C. In order to enhance the reactivity of the reactants, the hydrated gel rather than a calcined gel is used for hydrothermal synthesis. The factors that influence the reactivity of the gel are investigated. Also, the properties of synthetic and natural beidellites are characterized.; The disadvantages of pillared clays used as acid catalysts, especially as cracking catalysts, are their limited thermal and hydrothermal stability. This work reports a synthesis procedure for the preparation of alumina pillared montmorillonites that reliably affords products with exceptional performance properties, in particular, high BET surface area, microporosity, and Bronsted/Lewis acidity, when calcined at elevated temperatures. The approach utilizes a common pillaring agent (base-hydrolyzed AlCl{dollar}{bsol}sb3{dollar}) and typical montmorillonite compositions. However, certain synthesis and processing conditions that afford pillared products superior in structural thermal stability to those reported previously have been optimized. Also, the study focuses on the hydrolytic chemistry of the alumina pillar, which is a crucial factor in determining the thermal stability of the final product.; Alumina pillared beidellites, in addition to their thermal stability of up to 800{dollar}{bsol}sp{bsol}circ{dollar}C, exhibit high catalytic reactivity for the alkylation of biphenyl by propene. Furthermore, the pillared beidellites obtained from the H{dollar}{bsol}sp+{dollar}-exchanged form offer compatible thermal stability as well as catalytic activities that are superior to those of the corresponding pillared beidellites prepared from the Na{dollar}{bsol}sp+{dollar}-exchanged form.; New tubular silicate-layered silicate (TSLS) are obtained by the pillaring of imogolite (a tubular silicate) into a beidellite layer host. The TSLS is a pillared species in which the pillars themselves are microporous. The interests in this are the unique features of the TSLS complex which are different from the conventional pillared clays. Due to the hydrophilic structure of the imogolite tube, the swelling of the clay galleries by imogolite is reversible. The weak interaction between the pillar and clay host and microporous structure provide the possibility of building desired microporous pillared clays by simply adjusting the amount of microporous pillars intercalated during pillaring.