OMS-2深度催化氧化邻二甲苯的研究

发布时间：2018-01-12 11:34

本文关键词：OMS-2深度催化氧化邻二甲苯的研究　出处：《河北师范大学》2017年硕士论文　论文类型：学位论文

【摘要】：苯系污染物是最为常见的一类挥发性有机污染物(Volatile Organic Compounds,VOCs),会对人类和动物的健康造成严重的伤害。催化氧化技术以低耗能,高效率,无二次污染,可广泛使用等优点,在治理苯系污染物中受到众多科研工作者的关注。本文以常见的邻二甲苯为目标污染物,制备得到具有良好催化性能的氧化锰八面体分子筛(OMS-2)催化剂,并对其催化邻二甲苯的性能进行评价。具体内容如下:(1)以KMnO_4为氧化剂,分别以苯甲醇和Mn(NO3)2为还原剂,制备得到OMS-2催化剂(分别表示为B-OMS-2和N-OMS-2)。考察了还原剂对催化剂的结构和催化氧化邻二甲苯的性能的影响。SEM(Scanning Electron Microscope)分析表明,催化剂B-OMS-2呈现松散的立方体结构;XPS(X-ray Photoelectron Spectroscopy)显示B-OMS-2中几乎包含100%的Mn4+;TGA(Thermogravimetric Analysis)表明B-OMS-2中含有一些体相氧空位;FT-IR(Fourier Transform Infrared Spectoscopy)结果表明,在催化剂B-OMS-2中,苯甲醇可能吸附在MnO2的核上起到配体或结构导向剂的作用,与有机化合物的解吸作用共同导致了体相氧空位的形成。而XPS显示催化剂N-OMS-2中Mn4+和Mn~(3+)共同存在,且存在小的Mn~(3+)-氧空位基团。活性测试结果表明,在空速为8000h-1时,B-OMS-2可以在190℃时将邻二甲苯完全氧化为CO2,比N-OMS-2的温度低50℃。H_2TPR和O2-TPO结果表明,催化剂B-OMS-2具有良好的低温氧化性和较强的与分子氧的交换能力,这可能是其催化性能较好的原因。在抗水蒸气能力测试中,两种催化剂邻二甲苯转化率均为80%时通入5%的水蒸气,B-OMS-2的转化率降低了39%,N-OMS-2降低了27%,但停止通入后,两种催化剂的转化率均恢复到了原来水平。催化剂的原位漫反射红外光谱分析(In situ DRIFTS)发现,两种催化剂的催化氧化机理均符合MVK(Mars-van Krevelen)机制。催化剂B-OMS-2在晶格氧作用下120℃时可以氧化邻二甲苯侧链生成邻苯二甲醇,比N-OMS-2的温度低30℃。通入分子氧后,在50℃时将邻二甲苯侧链氧化至断裂,120℃时活化苯环,生成小分子羧酸盐和碳酸盐,300℃时将碳酸盐分解完全。而N-OMS-2在300℃时,中间产物并未被分解。上述结果表明,B-OMS-2具有更好的催化性能。(2)银、铜掺杂的催化剂Ag-OMS-2和Cu-OMS-2均可以提高OMS-2的催化性能。活性测试结果表明,催化剂Ag-OMS-2在190℃就可以将邻二甲苯完全氧化,比OMS-2和Cu-OMS-2的温度均低10℃;而催化剂Cu-OMS-2在T20(CO2产率为20%时的温度)时的温度为147℃,比OMS-2低了36℃,比Ag-OMS-2低了15℃。催化氧化反应前后的XPS表征结果说明,在催化剂Ag-OMS-2中Ag起着活性中心的作用,加速了活性氧物种的传递和循环,加快了整个催化氧化进程;催化剂Cu-OMS-2中仍是MnO2为活性中心,但铜的掺入提高了分子氧在Cu2O上的吸附能力,促进了MnO2/Mn2O3间的交换,有利于邻二甲苯的催化氧化。在三种催化剂转化率为80%时通入5%的水蒸气,Ag-OMS-2和OMS-2的转化率均降低了25%,Cu-OMS-2仅仅降低了6%,停止通入水蒸气后,三种催化剂的转化率都能恢复到80%。In-situ DRIFTS结果说明,三种催化剂催化氧化的反应机理都遵循MVK机制。催化剂Ag-OMS-2和Cu-OMS-2在晶格氧作用下,100℃时均能氧化邻二甲苯侧链生成邻苯二甲醇,比OMS-2温度低了20℃,但Ag-OMS-2在150℃时便能生成马来酸盐和碳酸盐;通入分子氧后,Cu-OMS-2在80℃时便能氧化邻二甲苯侧链,120℃使苯环活化生成小分子羧酸盐和碳酸盐,比Ag-OMS-2的温度低了20-30℃,但Ag-OMS-2在300℃时便可将邻二甲苯氧化生成的中间产物完全分解。掺杂银物种有利于羧酸盐和碳酸盐的分解,掺杂铜物种可以加速邻二甲苯的氧化进程。以上分析结果说明,银物种和铜物种的掺入均实现了对催化剂OMS-2的改良。
[Abstract]:Benzene series is the most common type of volatile organic pollutants (Volatile, Organic, Compounds, VOCs) can cause serious harm to human and animal health. Catalytic oxidation technology with low energy consumption, high efficiency, no two pollution, can be widely used in the advantages of treatment by many scientific researchers of benzene the pollutants. This paper takes o-xylene common as target pollutant, prepared has good catalytic performance of manganese oxide eight hedral molecular sieve (OMS-2) catalyst, and its catalytic performance of o-xylene was evaluated. The specific contents are as follows: (1) using KMnO_4 as oxidant, respectively with benzyl alcohol and Mn (NO3 2) as a reducing agent, was prepared by OMS-2 catalyst (denoted as B-OMS-2 and N-OMS-2 respectively). The effects of the performance of reducing agent on the catalyst structure and catalytic oxidation of o-xylene.SEM (Scanning Electron Microscope) analysis Show that the cube structure of catalyst B-OMS-2 presents loose; XPS (X-ray Photoelectron Spectroscopy) that the B-OMS-2 contains almost 100% Mn4+; TGA (Thermogravimetric Analysis) showed that B-OMS-2 contains some bulk oxygen vacancies; FT-IR (Fourier Transform Infrared Spectoscopy). The results showed that in B-OMS- 2 catalyst, benzyl alcohol may play a ligand or adsorption structure guide agent role in the kernel of MnO2, and the desorption of organic compounds leads to the formation of bulk oxygen vacancies. While XPS and Mn showed Mn4+ catalyst in N-OMS-2 ~ (3+) exists, and there is a small Mn~ (3+) - oxygen vacancy group. Activity tests showed that the space velocity is 8000h-1 when B-OMS-2 at 190 DEG C to o xylene complete oxidation of CO2, lower than the temperature of 50 DEG.H_2TPR and O2-TPO N-OMS-2 results showed that B-OMS-2 catalyst has good low-temperature oxidation and a Exchange ability with molecular oxygen, this may be the reason for its good catalytic performance. The steam resistance ability test, two kinds of catalysts of o-xylene conversion rate was 80% by introducing 5% of water vapor, reduce the conversion rate of B-OMS-2 was 39%, N-OMS-2 decreased by 27%, but the stop after conversion of two kinds of catalysts were restored to its original level. In situ analysis of diffuse reflectance infrared spectroscopy of catalyst (In situ DRIFTS) found that the catalytic oxidation mechanism of the two catalysts are in line with MVK (Mars-van Krevelen) mechanism. The catalyst B-OMS-2 can generate side chain oxidation of o-xylene phthalate two methanol in lattice oxygen under the action of 120 DEG C when the temperature of 30 DEG C lower than N-OMS-2. The molecular oxygen, O will be at 50 degrees C - xylene oxidation of side chain to rupture, activation of benzene at 120 DEG, to produce carboxylic acid salt and carbonate of small molecules, 300 degrees will be completely decomposition of carbonate and N-OMS-2 in 300. C, the intermediate product is not decomposed. The results showed that the catalytic performance of B-OMS-2 is better. (2) silver catalyst Ag-OMS-2 and Cu-OMS-2 copper doped can improve the catalytic performance of OMS-2 catalyst activity. The test results show that the Ag-OMS-2 at 190 DEG C can be completely oxidized o two toluene, than OMS-2 and Cu-OMS-2 low temperature of 10 DEG C; and the catalyst Cu-OMS-2 in T20 (CO2 yield is 20% when the temperature) at the temperature of 147 DEG, 36 DEG C lower than the OMS-2, 15 degrees lower than Ag-OMS-2. The characterization of XPS before and after the catalytic oxidation reaction shows that Ag plays a role in the active center of catalyst Ag-OMS-2, accelerated the reactive oxygen species transfer and circulation, accelerate the process of catalytic oxidation; Cu-OMS-2 catalyst is MnO2 as the active center, but the incorporation of copper increased the adsorption capacity of molecular oxygen on Cu2O, to promote the exchange between the MnO2/Mn2O3, is conducive to the neighbor The catalytic oxidation of xylene. The conversion rate of 80% into the 5% water vapor in three kinds of catalysts, Ag-OMS-2 and OMS-2 conversion rate was reduced by 25%, Cu-OMS-2 only decreased by 6%, stop feeding water, the rate of conversion of three catalyst can be recovered to the 80%.In-situ DRIFTS results showed that the reaction mechanism of three the catalyst for catalytic oxidation of the catalyst Ag-OMS-2 and follow MVK mechanism. The effect of Cu-OMS-2 on the lattice oxygen, can generate side chain oxidation of o-xylene phthalate two methanol at 100 DEG, 20 DEG C lower than the temperature of OMS-2, but Ag-OMS-2 at 150 DEG C to generate maleic acid salt and carbonate; pass into molecular oxygen then, Cu-OMS-2 oxidation of o-xylene side chain in 80 DEG, 120 DEG C to generate benzene carboxylic acid salt and carbonate of small molecules, 20-30 C lower than the temperature of Ag-OMS-2, but Ag-OMS-2 at 300 DEG C can be generated in o-xylene oxidation of intermediate product completely The doped silver species are favorable for the decomposition of carboxylate and carbonate. The doped copper species can accelerate the oxidation process of o-xylene. The above analysis results indicate that the incorporation of silver species and copper species has realized the improvement of catalyst OMS-2.

【学位授予单位】：河北师范大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：X51;O643.36

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