Physicochemical Characterization and Catalytic Application of Nanocomposite Oxides and Clay Based Nanoporous Materials for Synthesis of Some Biologically Important Molecules

Abstract

A series of MoO3-ZrO2 nanocomposite oxides with MoO3 content in the range of 2-50 mol% were prepared by coprecipitation, impregnation and combustion synthesis methods. The synthesized materials were characterized using different analytical techniques such as XRD, UV-Vis, SEM, TEM, Sorptometric and Raman techniques. The presence of MoO3 in the zirconia matrix found to selectively stabilize the tetragonal phase of zirconia. The crystallite size, surface area and the amount and strength of the acidic sites on the catalyst surface strongly depend on the molybdenum oxide content and the method of preparation. UV-Vis and Raman study of the composite oxide indicated the presence of isolated molybdate and polymolybdate clusters at low molybdna content whereas at higher loading presence of bulk type polymolybdates are observed on zirconia matrix. The effect of fuel nature and content of on the physicochemical characteristics of the MoO3-ZrO2 nanocomposite oxides was studied by taking three different fuel (urea, glycine and hexamethylenetetraamine) and F/O ratio in the range 0.5-1.5 in the combustion method. Nanocomposite oxides with better physicochemical properties are obtained using glycine as fuel. The catalytic activity of the coprecipitated samples was evaluated for the one pot synthesis of amidoalkylnaphthols and acetamidoketones. Similarly, the combustion synthesized samples were used as an efficient and environmentally benign catalyst for the synthesis of octahydroquinazolinones by multicomponent condensation reaction of dimedone, urea and arylaldehydes in aqueous media as well as under solvent free condition using microwave irradiation. Iron stabilized zirconia materials were prepared by coprecipitation method. Sulfate ions are grafted to the Fe2O3-ZrO2 surface by post sulfation method. The sulfate grafted Fe-Zr materials were characterized by XRD, UV-Vis, FTIR, SEM and TEM techniques. XRD study indicated the formation of a substitutional solid solution and selective stabilization of the tetragonal phase of zirconia. The presence of iron oxide in zirconia lattice improves the sulfate retention capacity of host zirconia. The catalytic application of SO42-/FeZr catalysts was studied for one pot synthesis of octahydroxanthene by condensation of dimedone and aryl aldehydes under solvent freecondition and microwave irradiation. The catalyst was found to be highly efficient for synthesis of structurally diverse octahydroxanthene giving good yield and purity of the products. Zr-pillared clay (Zr-P) was synthesized by insertion of zirconium oxyhydroxy clusters into clay interlayer and subsequent thermal activation. The Zr-P materials were treated with sulfuric acid to graft sulfate ions onto the zirconia nanopillars. The sulfate grafted Zr-pillared clay (SZr-P) was used as support for phosphomolybdic acid (PMA/SZr-P). The synthesized materials were characterized by XRD, IR, UV–Vis, SEM and sorptometric techniques. The expansion of the clay lattice as a result of pillaring was confirmed from X-ray diffraction study. The interlayer space was found to be retained in the PMA/SZr-P material. All pillared clay materials show Type-I sorption isotherm typical of microporous materials. The structural integrity of the phosphomolybdic acid in the clay matrix was ascertained from the IR and UV-Vis spectroscopy. The PMA/SZr-P material was used as an efficient catalyst for the one pot synthesis of -aminocarbonyl compounds by Mannich reaction in aqueous media. The multicomponent condensation of aryl aldehyde, amines and ketones using PMA/SZr-P material afforded a variety of -aminocarbonyl compounds in excellent yield and purity. Ceria based nanocomposite oxides, CeO2-CaO and CeO2-MgO, of different compositions were prepared by amorphous citrate process and citrate gel combustion process. These materials were characterized by using different analytical techniques such as XRD, TGA, UV-Vis-NIR, SEMand TEM. The XRD analysis of the CeO2-CaO oxide indicated the presence of a substitutional type solid solution for ceria rich composite oxides where as for the calcium oxide rich composite oxides, the presence of crystalline CaO was observed along with the solid solution phase. In case of CeO2-MgO material, a minor contraction in the lattice parameter was observed for the ceria component which has been ascribed to the formation of a small amount of nonequilibrium MgxCe1-x/2O2 solid solution. The catalytic activity of CeO2-CaO materials was evaluated for the aqueous phase synthesis of 2-amino-2-Chromenes in aqueous media. Similarly, CeO2-MgO nanocomposite oxides were used as heterogeneous catalyst for synthesis of β-nitro alcohols andarylidenemalononitriles. For the synthesis of both classes of compounds, the composite oxides showed excellent catalytic activity giving good yield and purity of products under ambient condition.