Synthesis, Characterization Of Metal Compounds Based On Keggin Polyxometalates And Their Applications In Esterification

Esterification is an important acid catalyst reaction and the corresponding products, carboxylic esters, have been taken as dissolvent and aromatics. Isoamyl acetate, with pear and banana aromas, is an important organic chemical product with wide application in alcohol, cosmetics and raw material of edible essence and it is also used as extraction agent in medicine preparation. Conventionally, the production of isoamyl acetate mostly derived by esterification of acetic acid with isoamyl alcohol over acidic catalysts such as H2SO4, HCl and H3PO4. However, these conventional catalysts are hampered by several inherent drawbacks, such as equipment corrosion, undesirable side reactions, inconvenient post treatment, plaguy catalyst recovery and environmental pollution. Thus, consideration R&D efforts have been made on the development of heterogeneous catalysts with high catalysis efficiency, good thermal stability, no corrosion to equipments and no pollution to environment.The aim of this thesis is to synthesize new polyoxometalates by phosphotungstic acid with transition metal, silver, ionic liquid and amino acid. The new catalysts were characterized by different analytical and spectroscopic techniques such as FT-IR, TGA, XRD, and 1H and 13C NMR. In particular, their acidic properties were probed by solid-state 31P MAS NMR of adsorbed trimethylphosphine oxide. The catalytic performances of various catalysts during esterification reaction for isoamyl acetate were illustrated and examined. Effects of operating variables were investigated and response surface methodology was utilized to optimize these variables. Moreover, a kinetic model for the esterification was also established and evaluated under the optimized experimental variables, which is reference for producting other esters.In the second chapter, a series of transition metal modification phosphotungstic acid had been successfully synthesized and exploited for catalytic conversion of acetic acid. Among them, the Ni0.5H2.0PW12O40 catalyst was found to possess Br(?)nsted and Lewis acid, leading to the highest catalytic activity. As illustrated by esterification of acetic acid with isoamyl alcohol over the Ni0.5H2.0PW12O40 catalyst, an optimal isoamyl acetate yield of 97.6% was achieved under reaction conditions:alcohol/acid= 1.05:1, catalyst amount= 5 wt%, reaction time = 1.5 h, amount of water-carrying agent= 8 mL and temperature= 373 K. Under the optimal conditions, the kinetic equation could be expressed as r=-dCA/dt=1.0×1010 exp(-81.89/RT)CACB,the active energy was 81.89 kJ/mol.In the third chapter, catalytic activities of silver modification phosphotungstic acid by using silver and heteropolyacid as precursors in esterification of acetic acid were evaluated. Among them, the AgH2.0PW12O40 catalyst was found to possess strong acidity, leading to the highest catalytic activity. The optimum conditions in presence of AgH2.0PW12O40 were obtained as follows:alcohol to acid molar ratio of 1.2:1, catalyst amount of 4 wt%, reaction time of 1.0 h, amount of water-carrying agent of 10 mL and temperature of 373 K, generating a high isoamyl acetate yield of 98.8%. Under these conditions, the kinetic equation could be expressed as r=-dCA/dt=1.87×1010 exp(-83.63/RT)CACB,the active energy was 83.63 kJ/mol.In the fourth chapter, catalytic activities of organic-inorganic hybrid materials combined by heteropolyacid and ionic liquid with sulfonic group in esterification of acetic acid were explored. The results showed that, in addition to the strong activity, the heteropolyacid-based ionic liquids exhibited excellent catalytic performance with unique pseudo-liquid property. The optimum conditions for synthesis of isoamyl acetate over [MIM-PSH]1.5H1.5PW12O40 were obtained by response surface methodology as follows:alcohol to acid molar ratio of 1.05:1, catalyst amount of 6 wt%, reaction time of 1.0 h, amount of water-carrying agent of 12 mL and temperature of 373 K, leading to a high yield of 98.2%. Under these conditions, the kinetic equation could be expressed as r=-dCA/dt=1.3×1011 exp(-88.46/RT)CACB,the active energy was 88.46 kJ/mol.In the fifth chapter, catalytic activities of organic-inorganic hybrid materials combined by heteropolyacid and glycine for synthesis of isoamyl acetate were studied, indicating that self-seperation property accouted for high activity. Acidic properties of [GlyH]xH3.0-xPW10O40 catalysts were characterized by the solid-state 31P-TMPO NMR approach, which shown that the catalyst with a Gly/TPA molar ratio of 1.0 was found to possess superacidic characteristics and steric effect, leading to the highest observed activity and an optimal ester yield. The optimum conditions for synthesis of isoamyl acetate over [GlyH]1.0H2.0PW12O40 were obtained by response surface methodology as follows:alcohol to acid molar ratio of 1.05:1, catalyst amount of 4.5 wt%, reaction time of 2.0 h, amount of water-carrying agent of 10 mL and temperature of 373 K, generating a high yield of 98.5%. Under the optimized conditions, the kinetic equation was obtained to be r=-dCA/dt=5.1×109 exp(-79.73/RT)CACB, the active energy was 79.73 kJ/mol.