【作者】 翟德伟；

【导师】 华伟明；

【作者基本信息】 复旦大学 ， 物理化学， 2010， 硕士

【摘要】 SO42-/MxOy型固体超强酸是一类很有应用潜力的新型绿色催化材料,环境友好,不腐蚀反应设备,易分离而且可重复使用,因此,近三十年来受到国内外催化研究者的广泛关注。SO42-/SnO2是具有最强表面酸性的催化剂之一,其酸强度至少与SO42-/ZrO2相当,在某些酸催化反应中SO42-/SnO2表现出比SO42-/ZrO2更好的反应活性。但是,与硫酸氧化锆相比,硫酸氧化锡催化剂的制备比较困难,导致有关SO42-/SnO2的文献报道很少。生物柴油作为一种清洁、可再生能源,具有广阔的应用前景。酯化和酯交换反应是制备生物柴油的两种主要方法。酸催化在反应中可以克服碱催化时带来的皂化反应、催化剂中毒问题,而固体超强酸具有强酸性和高活性,成为制备生物柴油催化剂研究的热点。采用共沉淀法合成了掺杂少量Fe2O3(0.2-3.0 mol%)的SO42-/SnO2固体超强酸,并用XRD、N2吸附、TG、Raman、DRIFTS、ESR、电位滴定等方法对其结构、织构性质和酸性进行了表征。选择月桂酸与甲醇的酯化和三乙酸甘油酯与甲醇的酯交换为探针反应模拟生物柴油的制备,考察催化剂的酯化和酯交换反应性能。结果表明,SO42-/SnO2催化剂中掺杂少量Fe2O3抑制了四方相SnO2晶粒的长大,从而提高了催化剂的比表面,有助于催化剂稳定更多的表面硫物种,增加了催化剂的酸性位。当Fe2O3添加量低于0.2mol%时,所有Fe都处于SnO2的晶格中,随着Fe2O3掺杂量的增加,形成了聚集态Fe2O3小晶粒。在月桂酸与甲醇的酯化和三乙酸甘油酯与甲醇的酯交换反应中,掺杂少量Fe2O3的催化剂其反应活性明显高于未掺杂的SO42-/SnO2,这与催化剂的酸性位增加有关。添加Fe2O3摩尔分数为1.0%的催化剂具有最高的反应活性,这是因为该催化剂的硫含量和酸性位最多,该催化剂上的酯化反应于60℃反应6 h后月桂酸转化率高达88.9%,酯交换反应于60℃反应8 h后三乙酸甘油酯转化率高达92.1%,在生物柴油的合成中表现出潜在的优越性能。而且,SO42-/SnO2在酯化和酯交换反应中的催化活性明显高于SO42-/ZrO2催化剂。同样方法制备了掺杂少量Al2O3(0.5-3.0 mol%)的SO42-/SnO2催化剂,并对其结构、织构性质和酸性进行了表征。实验结果表明,SO42-/SnO2催化剂中掺杂少量Al2O3抑制了SnO2的晶化和四方相SnO2晶粒的长大,提高了催化剂的比表面,有助于催化剂稳定更多的表面硫物种,增加了催化剂的酸性位,催化剂中的铝以六配位状态存在。在月桂酸与甲醇的酯化和三乙酸甘油酯与甲醇的酯交换反应中,掺杂少量Al2O3的催化剂其反应活性明显高于未掺杂的SO42-/SnO2,这与催化剂的酸性位增加有关。添加Al2O3摩尔分数为1.0%的催化剂具有最高的反应活性,这是因为该催化剂的酸性位最多。该催化剂上的酯化反应于60℃反应6 h后月桂酸转化率高达92.7%,酯交换反应于60℃反应8 h后三乙酸甘油酯转化率高达91.1%,在生物柴油的合成中表现出潜在的重要性。催化剂失活主要是由于有机物分子在催化剂表面的沉积,覆盖了一部分的活性位,导致催化剂直接重复使用时活性下降。通过焙烧方法,可以除去催化剂表面吸附的有机物,恢复大部分催化活性。失硫是催化剂失活的次要原因。同样方法制备了掺杂少量Ga2O3 (0.5-5.0 mol%)的SO42-/SnO2催化剂,并对其结构、织构性质和酸性进行了表征。和掺杂Al2O3类似,SnO2的衍射峰强度随着Ga2O3的含量增加有所减弱,说明掺杂少量Ga2O3抑制了SnO2的晶化和SnO2晶粒的长大。酸性表征结果显示,加入少量的Ga2O3能够明显增加SO42-/SnO2催化剂的表面酸性位。SO42-/SnO2中掺入少量的Ga2O3也可以明显提高其在月桂酸与甲醇的酯化及三乙酸甘油酯与甲醇的酯交换反应中的催化活性,添加Ga2O3摩尔分数为1.0%的催化剂具有最高的反应活性,于60℃酯化反应6 h后月桂酸转化率高达91.3%,于60℃酯交换反应8 h后三乙酸甘油酯转化率高达89.2%,在生物柴油的合成中表现出潜在的重要性。更多还原

【Abstract】 The type solid superacids of SO42-/MxOy are recognized as a class of novel catalytic materials which are green and have potential application. They have attracted much attention in recent thirty years, because they are noncorrosive, environmentally friendly, easily seperative and well reusable. The study indicates that SO42-/SnO2 is one of the strongest surface acidic catalysts, or at least the acid strength is as high as that of SO42-/ZrO2, and it could exhibit higher catalytic activities in many acid catalyzing reactions. Howerver, there have been few papers concerning SO42-/SnO2 catalyst for difficulty in preparation, compared with the relative ease of preparation for SO42-/ZrO2. Tin oxide gels were usually obtained as fine particles in conventional method, and a large part of the precipitates were passed through a conventional filter paper, resulting in their diminished yields.As a clean and regenerable energy source, biofuel is of wide application. Esterification and transesterification are the two kinds of major methods to synthesis biodiesel. This method has simple procedure, low dispense and stable product. The main catalysts are concentrated sulfuric acid and alkaline metal hydroxides. Furthermore, solid superacid catalysts in the reaction can overcome the base-catalyzed saponification and the catalyst poisoning problem, and they also have strong acidity and high activity. So it will become good catalysts in biodiesel preparation.Sulfated tin oxide catalysts promoted with Fe2O3 (0.2-3.0 mol%) have been successfully prepared via co-condensation method and characterized by isothermal nitrogen adsorption/desorption, powder x-ray diffraction (XRD), thermal gravimetric analysis (TG), Raman spectra, diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and ESR spectroscopy. The number of acid sites on the catalysts was measured by means of potentiometric titration of n-butylamine. Triacetin with methanol and lauric acid with methanol were used as the representative compounds for the investigation of the catalytic activity for transesterification and esterification. The results indicate the growth of SnO2 crystallites is inhibited in the presence of small amounts of Fe2O3, further enhance the surface of the catalysts and could stabilize more sulfur species on the surface of SO42-/SnO2. Acidity is also enhanced incomparison with conventional sulfated tin oxide. All irons exist in the tetrahedral SnO2 network when the content of Fe2O3 below 0.2 mol%. But the cluster of iron oxides will be formed increasing with the content of Fe2O3. As a result, the sulfated tin oxides promoted with appropriate amount of Fe2O3 have been manifested higher catalytic activity than conventional sulfated tin oxide in transesterification and esterification. At 1.0 mol% promoter content, the maximum conversion in lauric acid with methanol (6 h) and triacetin with methanol (8 h) reactions were about 88.9% and 92.1%, respectively. Moreover, the catalytic activity of SO42-/SnO2 is apparently higher than that of SO42-/ZrO2.A series of Al2O3-doped (0.5-3.0 mol%) sulfated tin oxide catalysts have been prepared by a co-precipitation method. The structures and textural properties of these catalysts were characterized using N2 adsorption, thermogravimetric analysis (TG), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), Raman spectroscopy, and 27Al magic-angle spinning nuclear magnetic resonance (MAS NMR) techniques. The number of acid sites on the catalysts was measured by means of potentiometric titration of n-butylamine. Their catalytic performances for the esterification of lauric acid with methanol and transesterification of triacetin with methanol were also investigated. The results showed that the addition of Al2O3 to sulfated tin oxide inhibite the growth of SnO2 crystallites, enhance the surface of the samples, stabilize more sulfur species on the surface of SO42-/SnO2 and improve the catalytic activity markedly. The SO42-/SnO2 catalyst doped with molar fraction Al2O3 of 1.0 mol% exhibited the highest activity. The lauric acid conversion was 92.7% after the esterification for 6 h and the triacetin conversion was 91.1% after the transesterification for 8 h on this catalyst. The remarkable activities of the Al2O3-doped catalysts are caused by an enhanced number of acid sites. Moreover, catalyst reusability and regeneration were studied in esterification and transesterification using 1.0 mol% Al2O3-SO42-/SnO2. The catalyst was calcinated to regenerate after each reaction. The results showed that the main reason for catalyst deactivation was due to reactant molecules covering the activity of the catalyst acid sites, through washing and calcination approach, the cover molecules could be removed to restore most effective acid sites, so that the catalytic activity was almost restored.A series of Ga2O3-doped (0.5-5.0 mol%) sulfated tin oxide catalysts have been prepared in the same method. The structures of these samples were characterized using X-ray powder diffraction (XRD), N2 adsorption, thermogravimetric analysis (TG), diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), Raman spectroscopy (Raman). The number of acid sites on the catalysts was measured by means of potentiometric titration of n-butylamine. Be similar with the catalysts doping Al2O3, SnO2 diffraction peak intensity was increased with the content of Ga2O3, mainly because of the presence of Ga2O3 inhibiting SnO2 grain growth. The results showed that adding a small amount of Ga2O3 could significantly increase the catalyst’s surface acidity in SO42-/SnO2. And the catalytic activity could be also enhanced remarkablely. Similarly, the 1.0mol% Ga2O3-SO42-/SnO2 catalyst exhibited the highest activity. The lauric acid conversion was 91.3% after the esterification for 6 h, and the triacetin conversion was 89.2% after the transesterification for 8 h on this catalyst.更多还原