本文選題：Si-Beta分子篩 + Sn-Beta分子篩　； 參考：《鄭州大學(xué)》2017年碩士論文

【摘要】：隨著煤、石油等不可再生資源的日益消耗,和人們對(duì)使用化石資源帶來的環(huán)境污染問題的關(guān)注,開發(fā)利用清潔、廉價(jià)的可再生資源受到國(guó)內(nèi)外學(xué)者的極大關(guān)注。植物生物質(zhì)是由植物通過光合作用利用太陽光、水和二氧化碳產(chǎn)生的,是一種來源豐富、廉價(jià)、零碳排放的可再生資源。糖類是植物生物質(zhì)的主要組分,利用糖類制備液體燃料和化學(xué)品,是一條重要的可再生資源利用途徑。乳酸及其酯是一種可從糖類制備的重要平臺(tái)化合物,廣泛應(yīng)用在食品、醫(yī)藥、化妝品、化工等行業(yè)中。為了克服現(xiàn)有發(fā)酵法制備乳酸及其酯的不足,近年來,研究者們開發(fā)了化學(xué)催化轉(zhuǎn)化法從糖類制備乳酸及其酯。以廉價(jià)、豐富的葡萄糖或蔗糖為原料,通過催化轉(zhuǎn)化法制備乳酸酯,是一個(gè)包含多步反應(yīng)的復(fù)雜過程。為了提高乳酸酯的收率,多種催化劑被用來催化這一反應(yīng)。在所研究的固體催化劑中,含氟體系水熱合成的Sn-Beta分子篩被認(rèn)為是催化糖轉(zhuǎn)化制備乳酸酯的性能最好的催化劑。但是,水熱合成Sn-Beta分子篩比較困難,凝膠中Sn物種的存在極大地抑制分子篩的成核和生長(zhǎng),因此,需要較長(zhǎng)的晶化時(shí)間(通常十幾至二十幾天),這極大地限制了Sn-Beta分子篩的應(yīng)用。本論文在文獻(xiàn)調(diào)研和課題組已有的工作基礎(chǔ)上,建立了一種快速合成Sn-Beta分子篩的方法,用于高效催化葡萄糖轉(zhuǎn)化制備乳酸酯。該法首先合成出純Si-Beta分子篩,然后通過研磨、焙燒將Sn前體與Si-Beta分子篩作用,將Sn引入分子篩骨架,得到Sn-Beta分子篩。該法大大縮短了Sn-Beta分子篩的制備周期。研究表明,Sn能否成功引入骨架與Si-Beta分子篩的結(jié)晶度密切相關(guān)。Si-Beta分子篩的結(jié)晶度較低時(shí),有較多內(nèi)部硅羥基缺陷位,有利于Sn引入骨架;相反,不利于Sn引入骨架。對(duì)于高結(jié)晶度的Si-Beta分子篩,我們通過堿處理脫硅產(chǎn)生了內(nèi)部硅羥基缺陷位,然后與Sn前體反應(yīng),成功制備了Sn-Beta分子篩。通過XRD、SEM、N2物理吸附、UV-vis漫反射光譜、吡啶吸附FT-IR、氘代乙腈吸附FT-IR等方法表征了制備的Sn-Beta分子篩的物理化學(xué)性質(zhì)。將從不同結(jié)晶度的Si-Beta制備的Sn-Beta分子篩用于催化葡萄糖轉(zhuǎn)化為乳酸甲酯反應(yīng)中,在160 oC反應(yīng)10 h,乳酸甲酯收率最高達(dá)到48%,高于直接水熱合成的Sn-Beta-F分子篩(35%)和脫鋁-補(bǔ)Sn兩步法制備的Sn-Beta-P分子篩(22%)。最后,考察了制備的Sn-Beta分子篩的循環(huán)使用性,發(fā)現(xiàn)該法制備的Sn-Beta分子篩循環(huán)使用過程中,乳酸甲酯收率逐漸提高,使用6次后,乳酸甲酯收率由37%升高到52%。通過表征使用后的催化劑,發(fā)現(xiàn)造成這種現(xiàn)象的原因可能是分子篩表面的非骨架Sn物種在反應(yīng)過程中流失,使骨架Sn活性位更易被接觸。
[Abstract]:With the increasing consumption of non-renewable resources, such as coal and petroleum, and people's concern about the environmental pollution caused by the use of fossil resources, the exploitation and utilization of clean and cheap renewable resources have attracted great attention from domestic and foreign scholars. Plant biomass is produced by plants using sunlight, water and carbon dioxide through photosynthesis. It is a renewable resource with abundant, cheap and zero carbon emissions. Carbohydrates are the main components of plant biomass. The preparation of liquid fuels and chemicals from sugars is an important way to utilize renewable resources. Lactic acid and its esters are important platform compounds which can be prepared from sugar. They are widely used in food, medicine, cosmetics, chemical industry and so on. In order to overcome the shortcomings of the existing fermentation methods for the preparation of lactic acid and its esters, in recent years, researchers have developed a chemical catalytic conversion method for the preparation of lactic acid and its esters from carbohydrates. The preparation of lactate from cheap and abundant glucose or sucrose by catalytic conversion is a complex process involving multi-step reactions. In order to improve the yield of lactate, a variety of catalysts are used to catalyze this reaction. Among the solid catalysts studied, the hydrothermal synthesis of Sn-Beta molecular sieve with fluorine system is considered to be the best catalyst for the conversion of sugar to lactate. However, hydrothermal synthesis of Sn-Beta molecular sieve is difficult. The existence of Sn species in gel greatly inhibits the nucleation and growth of molecular sieve. It takes a long time to crystallize (usually more than 10 to 20 days), which greatly limits the application of Sn-Beta molecular sieves. On the basis of literature investigation and research work, a rapid synthesis method of Sn-Beta molecular sieve was established, which was used to catalyze the conversion of glucose to lactate. In this method, pure Si-Beta molecular sieve was synthesized, then Sn precursor was calcined to react with Si-Beta molecular sieve, and Sn was introduced into molecular sieve skeleton to obtain Sn-Beta molecular sieve. The preparation period of Sn-Beta molecular sieve was greatly shortened by this method. The results show that the successful introduction of the framework is closely related to the crystallinity of the Si-Beta molecular sieve. When the crystallinity of the Si-Beta molecular sieve is low, there are more defects in the internal silica hydroxyl group, which is favorable to the introduction of the framework to Sn, whereas it is not conducive to the introduction of the skeleton to the Sn molecular sieve. For the Si-Beta molecular sieve with high crystallinity, Sn-Beta molecular sieve was successfully prepared by alkali desilication to produce the internal silica hydroxyl defect site, and then reacted with Sn precursor. The physicochemical properties of the prepared Sn-Beta molecular sieve were characterized by UV-vis diffuse reflectance spectroscopy (UV-vis), adsorption of pyridine with FT-IRand deuterated acetonitrile (FT-IR). The Sn-Beta molecular sieve prepared from Si-Beta with different crystallinity was used to catalyze the conversion of glucose to methyl lactate. At 160oC for 10 h, the highest yield of methyl lactate was 48, which was higher than that of Sn-Beta-F molecular sieve 35 prepared by direct hydrothermal synthesis and Sn-Beta-P molecular sieve prepared by de-aluminization and Sn supplementation. Finally, the reusability of the prepared Sn-Beta molecular sieve was investigated. It was found that the yield of methyl lactate increased gradually during the recycling of the Sn-Beta molecular sieve prepared by this method. After six times of use, the yield of methyl lactate increased from 37% to 52%. By characterizing the catalyst, it is found that the reason for this phenomenon may be the loss of non-skeleton Sn species on the surface of molecular sieve during the reaction, which makes the active sites of skeleton Sn more accessible.
【學(xué)位授予單位】：鄭州大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2017
【分類號(hào)】：O643.36;TQ225.24

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