Preparation, Characterization and Catalytic Applications of Pillared Clay Analogues and Clay-Polymer Composite Materials

Abstract

Cr-pillared montmorillonite clay (Cr-P) was prepared by intercalation of chromium oxyhydroxy cationic clusters into the clay interlayer and subsequent thermal activation. The Cr-P material was characterized by XRD, FTIR, UV–Vis and sorptometric techniques. The expansion in the clay lattice as a result of pillaring was confirmed from the XRD study. The UV–Vis study of the
pillared clay revealed the presence of Cr3+species as Cr2O3 nanoclusters inside the clay interlayer.The IR study was employed to show the presence of acidic and non-acidic hydroxyl groups in the pillared clays. The Cr-P material was used as an efficient heterogeneous catalyst for the synthesis of benzoxanthenes and octahydroxanthenes. The benzoxanthenes were synthesized by condensation of two mole of -naphthol with one mole of benzaldehyde. Similarly, the octahydroxanthenes were
synthesized by the condensation of two mole of dimedone with one mole aryl aldehydes.Structurally diverse xanthene derivatives were synthesized under solvent free conditions and microwave irradiation using Cr-P as heterogeneous catalyst. The Cr-P clay was used further as
support for dispersion of silicotungstic acid (STA). The STA particles were dispersed in the micropores of Cr-P clay by wet impregnation method. The synthesized materials were characterized by XRD, FTIR, UV-Vis, sorptometric, TGA, SEM and TEM techniques. IR and UV-Vis study illustrates the structural integrity of the STA particles in the micropores of the pillared clay. N2
adsorption/ desorption shows that the synthesized materials are microporous in nature. The catalytic
activity of the STA/Cr-P materials was evaluated for synthesis of 1,4-dihydropyridines (DHPs) by multicomponent reaction of aldehydes/chalcones, ethylacetoacetate and ammonium acetate.Structurally diverse DHPs are prepared by using aryl aldehydes and chalcones as starting materials.A series of Zr-pillared clay (Zr-P)-polyphosphoric acid (PPA) and Zr-pillared claysulfonated polyvinyl alcohol (SPVA) composites were synthesized by adopting different preparative strategies. Initially, the polymeric species were intercalated to the clay matrix with and without the use of structure expanding agent (CTAB).