【作者】 王丽霞；

【导师】 张文祥； 王振旅；

【作者基本信息】 吉林大学 ， 物理化学， 2010， 博士

【摘要】 本论文以工业应用为出发点,致力于合成对乙醇催化脱氢合成乙酸乙酯反应有较高催化性能的催化材料。我们将不同的过渡金属基催化剂应用到该反应中,并详细考察了各种催化剂对反应的催化性能,同时结合多种测试手段对催化剂的结构及表面性质进行了表征,并与催化剂反应性能进行了关联。文中我们还探讨了催化剂的活性中心以及反应机理等问题。通过对不同合成条件制备的MoSx/C催化剂的性能考察,我们发现硫化温度为400℃,硫化时间为2 h,以H2O为溶剂,(NH4)6Mo7O24为试剂,由钼酸铵硫化-还原法制备的催化剂对乙醇脱氢合成乙酸乙酯反应有较好的催化性能。通过文献学习以及实验事实,我们认为在该催化剂上,金属钼的配位不饱和中心(CUS)提供反应所需的脱氢活性中心,而催化剂表面的SH–则可以提供反应所需的酸中心。活性碳载体的氧化处理过程可以提高Mo物种在载体表面的分散度,从而可以达到提高催化剂反应活性的目的。通过对不同合成条件制备的Cu-Zr-O催化剂的性能考察,我们发现合成温度为60℃,以H2O为溶剂,Cu(NO3)2为试剂,Na2CO3为沉淀剂,400℃焙烧,由反滴法-共沉淀法制备的催化剂对乙醇脱氢合成乙酸乙酯反应有较好的催化性能。通过文献学习以及实验事实,我们认为在该催化剂上,金属Cu提供反应所需的脱氢活性中心,ZrO2提供反应所需的酸中心。催化剂预还原温度的考察结果表明,Cu0不但参与了乙醇脱氢生成乙醛的反应过程,同时也参与了从中间产物乙醛生成乙酸乙酯的反应过程,所以我们认为从中间产物乙醛生成乙酸乙酯的过程发生在Cu0与ZrO2的界面上。不同摩尔比的催化剂的反应性能考察结果表明,催化剂中的Cu0和Cu+物种在反应的过程中存在协同作用,而且这种协同作用更有利于乙酸乙酯的形成。我们也考察了三组分的Cu-Zr-Co-O催化剂、尖晶石结构的Cu-Al-O催化剂以及Mo2C/C催化剂对乙醇催化脱氢合成乙酸乙酯反应的催化性能。实验结果表明,在铜锆催化剂中添加少量的CoO可以提高催化剂的反应性能。Cu-Al-O催化剂和Mo2C/C催化剂对反应的催化性能并不是很理想,但它们是探索对该反应有较高催化性能的新催化材料的有益尝试。更多还原

【Abstract】 Ethyl acetate is an important chemical materials and a useful solvent that is widely used in adhesives, medicines, and extraction solvent of organic acids. Three main commercially processes are currently available to achieve the production of ethyl acetate, including esterification of ethanol with acetic acid, addition of ethylene to acetic acid, the Tishchenko reaction of acetaldehyde. However, there are still several problems associated to these processes, such as the toxicity of acetaldehyde or the corrosion of acetic acid. The process of direct transformation of ethanol to ethyl acetate can solve these problems, because of using only ethanol as feedstock.In this work, various transition metal catalysts are used in the reaction of direct transformation of ethanol to ethyl acetate, including molybdenum-based and copper-based catalysts, the catalytic performances of above catalysts have been investigated. The relationship between the structure, surface texture and the catalytic performance of catalysts was studied by combining different characterization means. The nature of active sites on the catalysts and the reaction mechanism were also discussed in this article. The main results and conclusions are as follows.1. Study on the catalytic performance of MoSx/C catalysts for ethyl acetate synthesisIn this part of work, we studied the activity of molybdenum sulfide catalysts in the reaction of direct transformation of ethanol to ethyl acetate. The results showed that the conversion of ethanol can reach 91.5% and the selectivity to ethyl acetate can reach 49.4% over MoSx/C (Mo=8.7 wt%) catalyst under following reaction condition: T=320℃, P=1 atm, LHSV=1 h-1. According to the literatures and our experimental facts, we believe that CUS can provide dehydrogenation active sites and SH- can provide acid sites for this reaction. The study has also indicated that formation of highly dispersed molybdenum species, which were observed on the activated carbon support with HNO3 pretreatment, was favorable for high catalytic activity. The treatment of activated carbon with HNO3 produced an increase of the surface oxygen groups. Interactions between metal and oxygen functional groups were developed and then favored the dispersion of active phase.The effect of preparation parameter on the catalytic performance of MoSx/C catalysts has been systemically investigated. The results show that MoSx/C catalysts which were prepared by sulfidation of (NH4 ) 6M o 7 O2 4 at 400℃for 2 h have a good catalytic performance. At lower sulfurization temperature (300℃), there are two molybdenum species (Mo5+ and Mo4+) on the surface of the catalyst, Mo5+ species is not conducive to the formation of ethyl acetate. The particle sizes of the active species become larger at higher sulfurization temperature (500℃or 600℃), so the catalytic performance decrease. MoSx/C catalyst which was sulfided at 400℃obtained the best catalytic performance. At shorter sulfidation time (1 h), the concentration of SH- on the catalyst surface is relatively small, lack of Br?nsted acid sites resulting in lower catalytic performance. MoSx/C catalyst which was sulfided for 2 h obtained the best catalytic performance. The drying atmosphere did not have much effect on the catalytic performance of the catalyst.2. Study on the catalytic performance of Cu-Zr-O catalysts for ethyl acetate synthesisIn this part of work, we studied the activity of copper-zirconium catalysts in the reaction of direct transformation of ethanol to ethyl acetate. The results showed that the conversion of ethanol can reach 70.9% and the selectivity to ethyl acetate can reach 78.8% over Cu-Zr-O (Cu︰Zr = 1) catalyst under following reaction condition: T=270℃, P=1 atm, LHSV=1 h-1. According to the literatures and our experimental facts, we believe that metal Cu can provide dehydrogenation active sites and ZrO2 can provide acid sites for this reaction. The prereduction temperature has a great influence on the particle size of Cu0 species. With an increase of reduction temperature, the particle size of Cu0 species increases. Changes in Cu0 particle size not only affect the rate of ethanol conversion, but also the selectivity of ethyl acetate. The result shows that Cu0 species not only involved in the dehydrogenation of ethanol to acetaldehyde, but also the process of ethyl acetate synthesis from acetaldehyde. So we believe that the process of ethyl acetate synthesis from acetaldehyde occurred on the interface of Cu0 and ZrO2 .The catalytic performances of Cu-Zr-O mixed oxides were considerably influenced by changing the molar ratio of Cu to Zr. The highest selectivity to ethyl acetate was found over catalyst which has the highest ZrO2 content. However, all the Cu-Zr-O catalysts show similar conversion of ethanol, which should be due to the fixed Cu content for these catalysts during the catalytic test. The characterization results show that the concentration of acid sites and also Cu+ species increase gradually with increasing ZrO2 content. These results suggest the positive correlation between the selectivity to ethyl acetate on Cu-Zr-O catalysts and the concentration of Cu+ species. According to the literatures, we believe that the presence of Cu+ species may be regarded as Lewis acidic sites, which are involved in acetaldehyde chemisorption, thus resulting in the improvement of ethyl acetate selectivity. Therefore, we suppose that the co-existence of Cu0 and Cu+ species in the Cu-Zr-O catalyst might play a synergic interaction for converting ethanol to ethyl acetate. The effect of preparation parameter on the catalytic performance of Cu-Zr-O catalysts has been systemically investigated. The results show that Cu-Zr-O catalysts which were prepared by coprecipitation of Cu(NO3)2 and Zr(NO3)4 with the addition of Na2CO3 at 60℃have a good catalytic performance. The characterization results show that the good catalytic performance can be attributed to smaller particle size of copper species and higher surface area of the catalyst. The calcination atmosphere did not have much effect on the catalytic performance of the catalyst. 3. Study on the other catalysts in ethyl acetate synthesis reactionIn this part of work, Cu-Zr-Co-O, Cu-Al-O and Mo2C/C catalysts were applied to the reaction of direct transformation of ethanol to ethyl acetate. We found that addition a small amount of CoO to Cu-Zr-O catalyst can improve the catalytic performance. The characterization results showed that the good catalytic performance can be attributed to the smaller particle size of copper species and also the appropriate Lewis acidic sites on the surface of the catalyst. Cu-Al-O catalysts have good stability. According to our experimental results, the conversion of ethanol can reach 55.1% and the selectivity to ethyl acetate can reach 63.5% over Cu-Al-O (Cu︰Al = 1) catalyst under following reaction condition: T=270℃, P=1 atm, LHSV=1 h-1. Mo2C/C catalysts were prepared by carbonization of Mo/D293 sample at 900℃under nitrogen. The results showed that the conversion of ethanol can reach 82.5% and the selectivity to ethyl acetate can reach 40.1% over this catalyst under following reaction condition: T=300℃, P=1 atm, LHSV=1 h-1. Although the catalytic performance of Cu-Al-O catalyst and Mo2 C/C catalyst is not good enough, it is still a useful attempt to explore the good catalytic materials for the reaction of direct transformation of ethanol to ethyl acetate.更多还原