金属—有机框架材料固载Au、Pd的制备及其催化性能的研究

发布时间：2018-06-15 04:34

本文选题：金属-有机框架材料 + 贵金属　；参考：《南昌大学》2017年硕士论文

【摘要】：金属-有机框架材料(MOFs)是金属离子与有机配体通过配位连接形成的三维多孔网状结构材料,它们具有高的比表面积、可调的孔径大小、不饱和金属位点、较高的热稳定性以及规整有序的纳米尺寸孔道,这些优点使得MOFs能作为独特的微反应器及理想载体。贵金属纳米颗粒(如Au、Pd等)因其特有的量子尺寸效应,在催化反应中往往表现出高效的催化活性,但其价格十分昂贵,在多相反应中分散度差,而且反应后很难回收,容易造成实验成本的浪费,通常都会考虑将其固载。因此在最近的研究中,MOFs材料因其独特的优点,通常作为首选载体对Au、Pd纳米颗粒进行固载。从其物理性质看,通过固载既能限域Au、Pd纳米颗粒的尺寸大小,又可以增大Au、Pd纳米颗粒的分散度,进而提高金属活性中心的分散度,催化活性也因此会有明显的提高;高比表面积性质使其存在大量的不饱和键,也相应的增加其表面台阶、皱褶和缺陷,其催化活性和选择性也随之提高。从工业经济角度看,相对于纯贵金属,固载型贵金属催化剂参与非均相反应,易于回收利用,更为经济。本论文在充分考虑到MOFs自身特点的情况下,设计合成了两种固载型催化剂,Au@MIL-101和Pd/MOF-808a。第一个工作中,注意到MIL-101自身3 nm左右的介孔孔道,利用其孔道对Au颗粒进行限域,制备3 nm左右的Au纳米颗粒。对Au@MIL-101进行了一系列表征,其结构表征可知,Au纳米颗粒能高度分散在MIL-101中,当Au浓度在一定范围内时,MIL-101的限域作用可以将Au纳米颗粒控制在3 nm左右,非常均匀,证明MIL-101对Au纳米颗粒起到了限域的效果。首次把Au@MIL-101运用于对硝基苯酚加氢反应中对它进行催化性能的测试,在温和条件下,该催化剂在对硝基苯酚还原反应中展现出十分优秀的催化活性,相对于传统的加氢催化剂表现出更小的活化能。在第一个催化剂的设计理念上,注意到单斜相的ZrO_2不仅具有酸催化性能,而且具有碱催化性能,原位红外研究证明其碱性来自氧化锆上存在的OH簇。考虑Zr-MOFs是由具有OH基的多原子无机Zr-O簇构成,其与氧化锆结构类似,我们提出一些Zr-MOFs可能具有布朗斯特碱性位点的设想。基于上述的思考,进行研究,开发出第一个具有B碱中心的Zr-MOF材料MOF-808a。通过验证,MOF-808在热的新鲜溶液中反应,MOF-808上的甲酸根会被t-OH取代,成为一种酸碱中心能均匀分散的材料,记作MOF-808a。具体证明过程如下:首先进行CO2-TPD-MS表征,分析发现MOF-808a对CO_2有很强的化学吸附,证明其存在碱中心;进一步进行酸滴定表征,从最终的数据谱图中,分析发现只有一个突变点,可判断在MOF-808a上面应该只有一种OH(b-OH或t-OH),PKb在10左右;最后对其进行原位红外的表征,观察不同温度下谱图中相应官能团的变化,发现MOF-808a上的OH最终归属为t-OH。为进一步证明MOF-808a的碱性作用,我们设计合成了催化剂Pd/MOF-808a,选择需引入碱参与的有机反应,包括Heck反应和苯甲醇氧化反应。该催化剂在Heck反应中,在不使用外加碱的情况下,转化率可达到93.6%,循环使用10次后,催化剂结构未发生明显变化,且催化效果依然保持在90%左右;在苯甲醇氧化反应中,该催化剂同样表现出优良的催化活性,与其他固载型催化剂相比,对产物表现出更高的选择性。通过上述两个探针反应,充分证明MOF-808a具有较强的碱性作用,相信这一发现,可以给其他科研工作者提供一点参考。
[Abstract]:Metal organic frame material (MOFs) is a three-dimensional porous network structure material formed by metal ions and organic ligands. They have high specific surface area, adjustable aperture size, unsaturated metal loci, high thermal stability and orderly and orderly nanoscale channel. These advantages make MOFs as a unique micrometer. The noble metal nanoparticles (such as Au, Pd, etc.) often exhibit high catalytic activity in the catalytic reaction because of their unique quantum size effect. However, the price is very expensive, and the dispersion is poor in the multiphase reaction, and it is difficult to recover after the reaction. It is easy to cause the waste of the experimental cost. Therefore, in recent studies, because of its unique advantages, MOFs is usually used as the preferred carrier to immobilizing the Au, Pd nanoparticles. From its physical properties, the dispersion of Au and Pd nanoparticles can be increased by immobilizing the limited domain Au, the size of Pd nanoparticles and the dispersion of Au and Pd nanoparticles, thus improving the dispersion of the metal active center and catalytic activity as well. Therefore, the high surface area properties make it have a large number of unsaturated bonds, and also increase their surface steps, wrinkles and defects, and their catalytic activity and selectivity also increase. From the industrial economic point of view, relative to the pure precious metals, the solid supported noble metal catalysts are involved in heterogeneous reaction, easy to recycle, and more easy to recycle. In this paper, two kinds of immobilized catalysts are designed and synthesized in this paper. In the first work of Au@MIL-101 and Pd/MOF-808a., the first work of Au@MIL-101 and Pd/MOF-808a. is to pay attention to the mesoporous pore of the MIL-101 itself around nm, and use its channel to limit the Au particles to prepare the Au nanoparticles about 3 nm. A series of Au@MIL-101 is made to Au@MIL-101. Characterization shows that Au nanoparticles can be highly dispersed in MIL-101. When the concentration of Au is within a certain range, the limiting effect of MIL-101 can be controlled at about 3 nm, very homogeneous, which proves that MIL-101 has a limited effect on Au nanoparticles. The first time Au@MIL-101 is applied to the hydrogenation of p-nitrophenol. The catalyst exhibits excellent catalytic activity in the reduction reaction of p-nitrophenol under mild conditions and shows smaller activation energy relative to the traditional hydrogenation catalyst. In the design concept of the first catalyst, it is noted that the monoclinic ZrO_2 has not only acid catalytic performance but also an acid catalytic performance. In situ FTIR performance, the in situ infrared study shows that its alkalinity comes from the OH cluster on zirconia. Considering that Zr-MOFs is composed of polyatomic inorganic Zr-O clusters with OH based, it is similar to the zirconia structure. We propose some ideas that Zr-MOFs may have the base site of the Bronx. Based on the above thinking, the first tool is developed. The Zr-MOF material MOF-808a. with B base is verified by the reaction of MOF-808 in the hot fresh solution. The formic acid roots on MOF-808 will be replaced by t-OH and become a kind of material with homogeneous dispersion in the center of acid and alkali. The specific process of proving MOF-808a. is as follows: first, CO2-TPD-MS is characterized, and MOF-808a is found to have strong chemical adsorption to CO_2, It was proved that there was an alkali center; further acid titration was carried out. From the final data spectrum, it was found that there was only one point of mutation. It was found that there should be only one kind of OH (b-OH or t-OH) and PKb at about 10 on the MOF-808a. Finally, it was characterized by in situ IR, and observed the changes of corresponding functional groups in the spectrum at different temperatures, and found MOF-8 The OH on 08A eventually belonged to t-OH. to further prove the alkaline effect of MOF-808a. We designed and synthesized the catalyst Pd/MOF-808a, and selected the organic reactions involving the introduction of alkali, including the Heck reaction and the oxidation of benzyl alcohol. In the Heck reaction, the conversion rate can reach 93.6% without the use of the applied alkali, and the catalyst can be recycled by 10. After that, the structure of the catalyst did not change obviously, and the catalytic effect remained at about 90%. In the oxidation of benzyl alcohol, the catalyst also showed excellent catalytic activity. Compared with other immobilized catalysts, the catalyst showed higher selectivity to the product. Through the reaction of the two probes, the MOF-808a was fully proved to be strong. It is believed that this discovery can provide some reference for other researchers.
【学位授予单位】：南昌大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：O643.36

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