| Heteropoly compounds are applied as catalysts for various organic in many areas, such as catalytic chemistry、material chemistry and analytical chemistry, because of their unique properities of strong acidity and redox. Physicochemical properties and catalytic properties of heteropoly compounds are closely related to the nature of heteroatoms, coordination atoms and counterions. So the combination of organic cations with heteropolyanions can cause the formation of organic-heteropoly compound, which may have special structure and properties. This is an important way of synthesize novel hybrid materials, and one of research hotspots of heteropoly compounds at present.A series of organic-heteropoly compound catalysts were prepared by two-step and impregnation method in this study. The catalytic activities were tested for the esterification of adipic acid with n-butanol. The influence of organic cations and heteropolyanions structure on the catalytic performances was investigated in detail. In addition, the structure and composition of catalysts were characterized by XRD, FT-IR and UV-Vis etc.A family of solid organic-heteropoly compound catalysts were prepared by combining heteropolyanions with ionic liquid-forming orgacnic cations( including methylimidazole(MIM), pyridine(Py), triethylamine(TEA), trimethylamine(TMA) and triphenylphosphine(TPP)) functionalized by propane sulfonate(PS) and butane sulfonate(BS). XRD and FT-IR characterization results indicate that the organic cation and heteropolyacid linked by the ionic bonding, and maintain the structure of heteropolyanion. The optimum reaction conditions for esterification are reaction temperature 283 K, mole ratio of n-butanol to adipic acid 3:1, mass ratio of toluene as water entrainer to reactants 13.5% and mass ratio of catalyst to adipic acid 7.6%. Under these conditions, the catalytic performance of the catalyst with PS as sultone agent was better than those of catalyst with BS as sultone agent. Among them, [TEAPS]3PW shown the best catalytic activity and 93.5% conversion of adipic acid was obtained after 3 h reaction.A series of organic-heteropoly compound catalysts based on PVP and heteropolyacids with different compostion and structure( PM(K)、PMo(K)、PMo(D)) were synthesized by the impregnation method. The new organic-heteropoly compound has good thermal stability, molar ratio of pyrrolidone monomer and heteropolyanion is 3:1, the structure of organic and inorganic component preserved. The effect of pretreatment temperature for heteropolyacids and hybrid catalysts, the composition and structure of heteropolyanion on the performance of catalysts for esterification reaction were investigated. The results indicated that the lower pretreatment temperature of catalyst is beneficial to improve the performance of catalyst in esterification reaction. Under the same treatment temperature, the catalytic activity sequence is: PVP-PMo(K) > PVP-PMo(D) > PVP-PW(K). In addition, catalyst PVP-PMo(K,35) can be well applied to a variety of esterification with different carboxylic acids and alcohols.A novel Preyssler-structured heteropolyacid was synthesized, and the catalytic performance for esterification of adipic acid with n-butanol was studied. Under the optimum reaction conditions: mole ratio of n-butanol to adipic acid 3:1, 1 g of catalyst, 288 K of reaction temperature, a 88.2% conversion of adipic acid was obtained after 3.5 h reaction. A series of organic-heteropoly compound catalysts based on Preyssler-structured HPA were synthesized by the two-step method. FT-IR results show that organic- heteropoly compounds remains Preyssler structure.The results showed that catalyst [TMABS]14PW(P) shown the best catalytic activities, and the conversion of adipic acid can reach 87.3% after 5 h reaction. The solid catalyst could be conveniently recovered by filtration and easily recycled into the next run, and the heteropolyanion remained Preyssler structure after a five-run recycle. |
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