【作者】 韩美凤；

【导师】 刘漫红；

【作者基本信息】 青岛科技大学 ， 有机化学， 2009， 硕士

【摘要】 粒径在1¹0 nm的纳米金属簇在学术界和工业中特别是催化领域受到了广泛的关注。表面活化剂稳定的纳米簇并不稳定,甚至在比较温和的反应条件下都会发生团聚,而高分子稳定的金属簇是稳定的,因此可以应用于许多催化反应中。氯代芳烃毒性极大,并在环境中难以降解。本文选择低氯取代的一氯代苯为研究对象,进行了以下几个方面的研究:首先,以PVP为保护剂,甲醇为还原剂,甲醇和水为混合溶剂,通过调节H₂PtCl₆·6H₂O的量、PVP用量以及回流过程中搅拌停止的时间等制备得到一系列不同的Pt纳米金属胶体催化剂,并用透射电镜进行了表征。PVP用量以及H₂PtCl₆·6H₂O的量发生改变时,胶体粒径没有发生明显的变化,但是,胶体制备过程中PVP用量过少时,胶体颗粒呈现一定程度的聚集。在胶体制备过程中,停止搅拌时间越长,得到的胶体粒径越大,分布越宽,当停止搅拌时间为30 s时,胶体的平均粒径由3.63 nm增大至4.39 nm,粒径分布最宽（σ= 0.78 nm）并且出现大量胶体粒子聚集的现象。第二,在常温常压下,以PVP-Pt胶体为催化剂,进行了氯苯的催化氢化反应。PVP-Pt胶体加速了氯苯的还原脱氯。反应可以在温和的条件下有效进行。氯苯10 h内脱氯率达到99.34 %,对环己烷的选择性达到98.09 %,反应15 h时,氯苯完全转化为环己烷。催化剂的制备条件及反应条件的改变对氯苯的脱氯反应有明显的影响。1、胶体制备过程中,PVP用量不同得到的金属胶体的催化性能排序如下:PVP-Pt4>PVP-Pt5>PVP-Pt3。2、反应过程中补加PVP,氯苯的转化率及对环己烷的选择性都有一定程度的下降,这说明PVP对反应有轻微的阻碍作用;在反应体系中增大补加PVP的用量（PVP-Pt42,PVP:Pt = 80:1）,对环己烷的选择性下降,但是氯苯的转化率几乎没有发生变化。数据表明,PVP更易影响反应的选择性。3、胶体制备过程中金属前体的浓度降低,反应的转化率,选择性都随之下降,对环己烷的选择性下降尤为明显。4、催化剂制备过程中停止搅拌时间不同,得到的催化剂的催化性能明显不同,停止搅拌时间越长,催化剂的催化性能越差。当停止搅拌时间为30 s时,催化剂的平均粒径由3.63 nm增大至4.39 nm,出现大量聚集的现象。氯苯的转化率由99.34 %降低到79.06 %,对环己烷的选择性也由98.09 %降低到74.40 %。5、在底物量相同的情况下,催化剂浓度低于1.7×10^-6 mol/mL时,氯苯的转化率随着催化剂浓度的增加呈非线性增加,当催化剂浓度高于1.7×10^-6 mol/mL时,氯苯的转化率不受催化剂浓度的影响;在催化剂浓度相同的情况下,氯苯转化率对氯苯浓度是一级反应。6、通过氯苯脱氯的动力学研究,发现氯苯的脱氯符合准一级反应,速率常数为0.5026 h^-1。第三,研究了金属离子对PVP-Pt催化氯苯氢化反应的修饰作用。结果表明,在氯苯选择氢化为环己烷的反应中,加入的金属阳离子能显著影响铂胶体催化剂的催化性能。其中Al3+的修饰作用最好,Al3+使氯苯的转化率由77.49 %提高到90.64 %,对环己烷的选择性由65.58 %提高到72.24 %。第四,研究了有机配体和金属络合物对PVP-Pt催化氯苯氢化反应的修饰作用。结果表明,金属配合物和配体的引入对催化剂的催化活性和选择性有很大的影响。当以纯PVP-Pt胶体为催化剂时,氯苯的转化率为77.49 %,对环己烷的选择性为65.58 %。乙酰丙酮配体可以同时提高催化活性及选择性,催化活性由77.49 %提高到90.85 %,选择性由65.98 %提高到68.45 %。研究表明,金属配合物对金属胶体的修饰作用并不仅仅是金属离子和配体的简单加和。金属配合物效应与金属络合物、反应底物、反应产物和金属催化剂之间的相互作用有关。由于金属配合物存在逐级解离,产生了配体和金属离子不同配比的多级配合物,从而导致金属配合物的修饰作用机理十分复杂。更多还原

【Abstract】 Metal nanoclusters in the range of 1-10 nm are very important in academia and industry, especially in the field of catalysis. However, the surfactant-stabilized metal clusters are not stable and intend to agglomerate during reaction even under very mild conditions. Thus, the polymer-stabilized metal clusters are extremely important for their catalytic use.Chlorinated organic compounds have been used on a large scale in chemical, petrochemical, and electronic industries. Those compounds are widespread environmental contaminants. They are of great health and environmental concern besaused of their acute toxicity and strong bioaccumulation potential. Among all, the chlorinated aromatic compounds are most toxic and thermally stable. Once released into environment, they will accumulate in the surrounding and endanger human as well as its ecological environment over a long period of time. In this paper, chlorobenzene was chosen as model compounds for the study of hydrogenation over polymer-stabilized platinum colloidal catalysts. Methanol was chosen as the solvent since it allows us to investigate the HDC reaction at a high concentration of the water-insoluble halogenated compound.Firstly, poly （N-vinyl-2-pyrrolidone）-stabilized platinum colloids （PVP-Pt） were prepared by varying the amount of H₂PtCl₆·6H₂O, the amount of PVP and stirring stopping time after discoloring solution for 5 min in methanol and water mixed sol-vents. The metal colloids were characterized by TEM. No significant effect on parti-cle size was observed by varying the amount of H₂PtCl₆·6H₂O and the amount of PVP. But the Pt nanoparticles have a tendency to aggregate because of the small amount of the stabilizing polymer. The longer stirring stopping time was in the preparation of colloidal platinum, the larger the particle size and size distribution were. When the time of stopping stirring was 30s, the largest particle size （4.39 nm） and the widwst size distribution （σ= 0.78 nm） could be obtained.Secondly, hydrogenation of monochlorobenzene （MCB） was carried out in a batch mode using hydrogen over PVP-Pt at 298 K and atmospheric pressure. The product consisted of benzene and cyclohexane during the reaction, and nearly 100 % selectivity to cyclohexane can be obtained at 100 % conversion of MCB. The catalytic performance of the PVP-Pt colloids is dependent on the preparation conditions. The small amount of the stabilizing polymer （PVP） in the preparation of colloidal platinum could not protect the platinum colloid commendably, but the large amount of PVP hindered the contact of reactant with catalyst surface and desorption of product. Extra PVP added in the reaction system has some inhibiting effect on the reaction activity, and also resulting in some decrease in selectivity to cyclohexane. The performance of catalyst was proportional to the concentration of H2PtCl6?6H2O. The catalytic properties of catalysts were affected remarkably by the time of stopping stirring in the preparation of catalysts. The conversion and the selectivity could be down to 79.06 % and 74.40 %, respectively, by prolonging the time of stopping stirring to 30 s. The reaction was verified to be first order to the concentration of MCB. The reaction is kinetic control at lower catalyst concentration （< 1.7×10-6 mol/mL）, and the diffusion controls the reaction when the catalyst concentration beyond 1.7×10-6 mol/mL. The reaction took place on the metal surface in a pseudo-first-order reaction, and the rate constant was 0.5026 h-1.Thirdly, effect of metal ions on hydrogenation of chlorobenzene （MCB） over poly-vinylpyrrolidone stabilized platinum colloid （PVP-Pt） was studied. It was shown that the catalytic properties of platinum clusters for the hydrogenation of chlorobenzene to cyclohexane were remarkably affected by the metal cations added. Among these cations, the most favorable influence on the activity and selectivity was obtained when Al3+ was used as modifier. The conversion of chlorobenzene was enhanced remarkably from 77.49 % to 90.64 %, and the selectivity for cyclohexane was increasd from 65.58 % to 72.24 %.Finally, effect of metal complex on hydrogenation of chlorobenzene （MCB） over PVP-Pt has been studied. It was shown that the addition of metal complexes and ligands to the catalytic system had great effect on activity and selectivity of the catalyst. When the neat platinum cluster was served as the catalyst, only 77.49 % conversion of chlorobenzene and moderate selectivity for the cyclohexane （65.58 %） were obtained. On the addition of the ligands acetylacetone, the conversion and the selectivity were increased together （the conversion was 90.85 %, the selectivity was 68.45 %）. It was indicated that the effect resulted from the incorporation of metal complexed was not the simple sum of those of the corresponding metal central ions and the ligands. The complex effect is related to the interaction of metal complex with reaction substrate, reaction product or the metallic catalyst, etc. Owing to the equilibrium of step dissociation of metal complexes, there is a mixture of multistep complexes at an integer molar ratio of ligand to metal. This causes the mechanism of metal complexes effect very complicated.更多还原