Supported Heteropoly Acids and Multicomponent Polyoxometalates as Eco-Friendly Solid Catalysts for Bulk and Fine Chemicals Synthesis

Abstract

Supported heteropoly acids are an important class of eco-friendly solid catalysts which offer strong acidity or redox properties. Part 1 of this chapter gives the detailed description of Keggin heteropoly acids such as silicotungstic acid (STA) and phosphotungstic acid (PTA) supported on zirconia as thermally stable, reusable solid catalysts which can be used for variety of organic transformations such as alkylation, acylation, and allylation. The catalysts are characterized by various techniques such as X-ray diffraction, N2 sorption measurements, DTG–DTA, UV–Vis spectroscopy, FTIR pyridine adsorption, NH3-TPD, FT-Raman, and 31P MAS NMR. These supported HPA catalysts found to be highly active and selective with a long catalytic lifetime in the discussed reactions. Part 2 of this chapter describes the preparation of inorganic–organic hybrid materials by immobilization of molybdo-vanadophosphoric acids onto mesoporous silicas such as MCM-41, MCM-48, and SBA-15. The study has been further extended to mesoporous carbon and ethane-bridged SBA-15. All catalyst materials were characterized by elemental analysis, FTIR, N2 physisorption measurements, XRD, UV/Vis, XPS, CP-MAS-NMR, SEM, and TEM for their structural integrity and physicochemical properties. These materials were applied for various selective and controlled oxidation processes to develop environmentally benign protocols for synthesis of fine chemicals and tried to study their mechanisms. Further, a simple cation exchanged form of H5[PMo10V2O40]·32.5H2O supported on ionic liquid-modified SBA-15 (V2ILSBA) and its application in catalyzed aerobic oxidation of primary and secondary alcohols to corresponding aldehydes and ketones with no trace of over oxidation has been discussed.