The Preparation Of Nano-Metal Oxides As Green Catalysts And Their Applications In Organic Reactions

Nano-catalysts were known as the fourth generation catalysts in international, which were developed along with the application of nano-technology in the field of heterogeneous catalysis. Campared to the traditional catalytic materials, the nano-materials had conspicuous advantages, such as large specific surface area, high surface energy, more active sites, short crystal internal diffusion channel, etc. Therfore, nano-catalysts always played an important role in the chemical industry. So far, people have designed and synthesized many types of nano-catalysts, including carbon nano tube, metal nanoclusters, metal oxide nanoparticles, nano zeolites, nanofilm, etc. These nano-catalysts revealed excellent catalytic performance in various chemical reactions. How to develop eco-friendly nano-catalysts and extend their application scope would be the key in the future research.In this thesis, we have studied the applications of nano-catalysts in organic reactions in the following areas:Chapter1:An overview of the feature, classical preparation methods, and the most representative examples of nano-catalysts. We introduced the applications of nano-catalysts in various fields containing environment, chemical industry and energy sources; and the present development status and market prospect were also summarized.Chapter2:We prepared a series of metal ions doped titanium dioxide nano-catalysts (M-TiO2) through a facial co-precipitation approach at room temperature. Their catalytic activities were evaluated via the liquid-phase oxidation of styrene, benzyl alcohol, toluene and benzylamine. To the best of our knowledge, this is the first example of metal ions doped TiO2nanoparticles catalyzing the selective oxidation of organic compounds without light irradiation.Chapter3:The oxidation of styrene catalyzed by disparate M-TiO2nano-catalysts was studied. The reaction conditions of the species of metal ions and doping amounts, solvents, calcination temperatures, recycling times were opitimized. The proposed mechanism of the styrene oxidation reaction was also discussed in detail. The catalyst Cu-10was favorable to produce chlorine-free benzaldehyde (96%), while the catalyst Co-15was beneficial to form styrene oxide (80%). Furthermore, the M-TiO2catalysts showed catalytic activities for the liquid-phase oxidation of benzyl alcohol and toluene to generate chlorine-free benzaldehyde.Chapter4:V-TiO2nanoparticles were acted as efficient catalyst in the oxidation of benzylamine at room temperature. The reaction conditions of catalyst amount, reaction time, calcination temperatures of catalyst and solvent effect were optimized. The results displayed that the maximum activity was found over the original catalyst V-15, which gave a95%conversion of benzylamine in excellent selectivity of benzylamine (>99%) in the presence of catalytic amount V-15(0.2g) when acetonitrile was used as solvent within10hours. The catalyst V-15could be recycled for six times without sensible loss of activity (the conversion of substrate remained over83%).Chapter5:We designed and synthesized a series of green magnetic solid acid nano-catalysts ZrO2-Al2O3-Fe3O4(ZAF), which were characterized by means of crystalline structure, morphology, magnetic property, the species and amounts of acid sites, thermostability. Compared to the classical solid superacid catalysts (SO42-/MxOy), the ZAF catalysts displayed high catalytic activities didn’t need to be impregnated by SO42-and calcined at high temperatures. The catalytic behaviors of these ZAF catalysts were investigated via esterification, the synthesis of bis-indolylmethanes, Hantzsch reaction, Biginelli reaction and Pechmann reaction. Meanwhile, the ZAF catalysts could be separated and recovered easily by an external magnet.Chapter6:The synthesis of n-butyl acetate was chosen as a probe reaction to examine the catalytic performance of the prepared ZAF nano-catalysts. The results indicated that the maximum activity was found over the catalyst ZAF-16/16, which gave a90%conversion of substrate in excellent selectivity of n-butyl acetate (>99%). Simultaneously, the catalyst ZAF-16/16demonstrated an excellent catalytic efficiency in the synthesis of bis-indolylmethanes (19kinds of target products). The recycling results showed that the catalyst ZAF-16/16could retain almost its initial activity up to five reaction cycles, and the loss of the nano-catalyst during the separation process was negligible. In addition, the catalyst ZAF-16/16also could facilitate the synthesis of7-hydroxyl-4-methyl coumarin.Chapter7:To further extend the application scopes of ZAF magnetic solid acid nano-catalysts, the as-prepared catalysts were also applied in mutil-component reactions. We have introduced the catalyst ZAF-16/16into the Hantzsch reaction, and the corresponding products (16kinds of1,4-dihydropyridines) were obtained in the presence of catalytic amount ZAF-16/16(0.05g) when refluxing in ethanol. The optimal catalyst ZAF-16/16was also used to facilitate the Biginelli reaction, the target products were achieved in moderate to good yields at140℃within5hours when using ethylene glycol as solvent. The Biginelli reaction proceeded smoothly when both urea and thiourea were used to afford the corresponding products, covering17kinds of3, 4-dihydropyrimidin-ones and14kinds of3,4-dihydropyrimidin-thiones.