Preparation and characterization of the bentonite supported HPA catalysts and their application on the esterification reactions

IV SUMMARY Clays are hydrated aluminium silicates which are formed by the chemical decomposition of volcanic feldspate rocks. Bentonite, which was used as a catalyst supporting material after purification, was obtained from Tokat-Reşadiye region in Turkey. Bentonite was used as the material. Two different type of heteropoly acids (H3PW12O40, H3PM012O40 and will be pronounced HPA hereafter) were used the catalyst active material. The catalysts were prepared in the following ways. Ten different catalysts were prepared by the impregnation of different amounts of HPAs to pure bentonite. These catalyst samples were characterized different techniques. Catalytic activities of prepared cataysts were tested in the acetic acid- benzyl alcohol esterification reactions. Thermogravimetric (TG) analysis of the samples were carried out for the determination of the amounts of hydroscopic water or crystal lattice water and the changes of the structures such as decompositio, and also investigation of thermal stability of the catalysts. Spesific surface area values were determined at 77K with the adsorption of N2 according to the B.E.T. method. Adsorption-desorption isotherms and B.E.T. graphs were drawn. Specific surface areas, avarage pore radius and pore volumes were determined by the means of the above mentioned curves and graphs. FTIR spectra of the bentonite, pure HPAs and all catalyst samples were recorded in a form of KBr discs. For the determination of the surface acidity of the catalyst samples, at first the surface of the samples were degassed with high vacuum at room temparature. Then, pyridine were adsorbed to samples in gas phase at different times. Finally, the surface of the samples were emptied after adsorption at high vacuum and once again at room temparature. All these process were monitored by FTIR specroscopy. Catalytic activity of the samples were tested in the acetic acid- benzyl alcohol esterification reactions. These reactions were carried in the presence of equal amounts of the catalysts at 30°C. Reactions were monitored by GC spectroscopic techniques.