【作者】 谢勇冰；

【导师】 刘昌俊；

【作者基本信息】 天津大学 ， 化学工艺， 2009， 博士

【摘要】 等离子体还原是一种有效的绿色还原过程,相对于常规的化学还原方法,等离子体还原时可避免使用化学还原剂,由此制备得到的负载型催化剂具有分散好,活性高等诸多优点。近年来等离子体技术开始出现一种新的研究方向,即将等离子应用在溶液中,制备纳米颗粒或促进化学反应。离子液体由于不可挥发性、较宽的电化学窗口和热稳定性等优异的物理化学性质,在化学反应和电化学沉积过程中有越来越重要的作用,已被称为“绿色溶剂”。本文将等离子体和离子液体相结合发展离子液体等离子体技术,尝试在离子液体中用等离子还原制备纳米颗粒,得到和常规还原不同的实验结果。由此进一步制备负载离子液体的高分散催化剂并将其应用到Suzuki反应中。由于离子液体发展较晚,有很多性质还不太清楚,我们首次对等离子体条件下离子液体的稳定性进行了考察。利用液体核磁共振和红外光谱,对等离子体处理前后三种离子液体[bmim]Cl、[bmim][BF4]、[bmim][PF6]的特征出峰情况进行了对比,核磁共振结果表明只有[bmim]Cl略有变化,进一步的红外吸收光谱表明三种离子液体都非常稳定,红外照相的结果表明整个处理过程都是在室温范围内进行。随后在[bmim][BF4]中用辉光放电等离子体还原PdCl2和HAuCl4得到纳米尺度的Pd和Au颗粒。还原得到的Pd为分散均匀的球形颗粒,平均粒径为4.9 nm左右,而金颗粒较大,平均粒径超过30 nm,且有轻微的团聚现象。论文进一步采用了次大气压辉光放电在离子液体液体[bmim][BF4]中还原贵金属盐,采用了间距更小的大平行板电极,经过放大之后可具有更高的处理效率。处理过程中观测到辉光放电对玻璃片的表面改性作用,经过等离子体处理的玻璃片,和离子液体的浸润作用大大增强。同时采用红外光谱对等离子体处理前后纯离子液体和溶解有Pd(NO3)2的离子液体的稳定性进行了考察,从红外出峰情况来看离子液体依然保持稳定。由此等离子体还原得到分散非常均匀的球形颗粒,平均粒径为5 nm左右。论文还引入稳定剂聚乙烯吡咯烷酮(PVP)来控制在离子液体中等离子体还原得到的纳米金颗粒,在不同的处理时间下得到的颗粒大小和形状均明显不同。在1分钟和5分钟还原时得到分散很好的单个颗粒,形状多样。延长时间用间歇法处理时,可明显看到大量花生状金颗粒和不规则金纳米线的出现。通过HRTEM观测,这些纳米结构是通过Au(111)面之间的作用连接起来的,Au(111)面之间的夹角在0到180o的范围内变化。这种结构的形成,是由于线性PVP分子和Au之间的相互作用,使得还原得到的Au团簇沿着PVP排列,还原得到的颗粒之间的接触机会大大增多,于是连接成长度不等的线式结构。XRD的结果表明这些不规则金颗粒的体相结构是典型的面心立方。改变稳定剂的浓度,也会对颗粒的形貌有很大影响。在一定的浓度下,可以得到很均一的颗粒。在SBA-15负载Au、Pd的催化剂上加上离子液体[bmim][PF6]制备负载离子液体催化剂。和不加离子液体相比,等离子体还原得到的金颗粒不再沿着SBA15孔道内生长成纳米线,而是形成分散很好的单个颗粒。金颗粒的大小随着担载量的提高逐步增大,0.5%的Au载量时为6.6 nm,载量提高到5%时颗粒大小也仅略大于孔道直径。负载离子液体后,等离子体还原得到的Pd颗粒也比不负载离子液体时要小3 nm左右。XRD结果表明还原得到的Au和Pd颗粒都是面心立方结构。负载Pd和离子液体的催化剂应用在Suzuki反应中显示出良好的活性,改变不同的前驱体和离子液体浸渍顺序,发现先浸渍Pd(NO3)2后浸渍离子液体[bmim][PF6]得到的催化剂效果最好。更多还原

【Abstract】 Plasma reduction is an effective green chemistry reduction process. Comparing to conventional chemical reduction,plasma reduction requires no hazardous reducing agents. The supported catalysts after plasma reduction have higher dispersions and show better catalytic activities. Ionic liquids, be composed of entire organic ionics and in liquid state in room temperature, are playing a more and more important role in chemical reactions or electrochemical depositions. Because of some unique properties, such as invotalizability, wide electrochemical windows and high thermal stability, ionic liquids were called green solvents. In this paper we combine plasma technology with ionic liquids to develop liquid plasma techniques. We intended to synthesize nanoparticles in ionic liquids via plasma reduction, and prepare highly dispersive supported ionic liquid catalysts.As ionic liquids have been developed for a relatively short time, people are not familiar with all of their properties. We investigated the stability of ionic liquids under glow discharge plasma for the first time. Three imidazolium based ionic liquids, [bmim]Cl, [bmim][BF4] and [bmim][PF6] showed their characteristic peaks in 1H NMR and FTIR. Only chemical shifts of [bmim]Cl in NMR changed a little but that was not an evidence of structure change. FTIR results confirmed that three ionic liquids were stable. All processes were at room temperature according to Infrared images. [bmim][BF4] was used as solvent, in which glow discharge reduced HAuCl4 and PdCl2 to prepare nanosized Au and Pd particles. Au nanoparticles formed in this process were little aggregated. The average particle size was 32.7 nm. The prepared Pd particles were well dispersed spherical particles in TEM results. The average size was 4.9 nm.Further more, Hypo-atmospheric pressure glow discharge (HAPGD) was used to reduce Pd(NO3)2 in [bmim][BF4]. The surface modification of plasma to the glass was observed during this process. [bmim][BF4] keep unchanged after HAPGD treatment, according to FTIR results. Pd nanoparticles reduced in ionic liquids were uniform and spherical, with an average size around 5 nm.Poly(vinyl pyrrolidone) (PVP) was imported into ionic liquids to control the Au nanoparticles formed after plasma reduction. The sizes and shapes were quite different with different reduction time. The products were mainly separate particles with various shapes after 1 minute or 5 minutes plasma reduction. In the processes with longer reduction time, peanut-like structures and irregular nanowires were formed. These nanostructures are connected through Au (111) planes, according to HRTEM results. The angles between two Au (111) planes varied from 0o to 180o. The action between PVP and Au clusters made these reduced Au clusters array along linear PVP molecules. Thus Au clusters had more chances to contact with each other to form linear shapes. XRD results showed that these irregular shapes were typical face-centered cubic structure. The concentration of surfactant was another important influencing factor to the Au particle sizes and shapes. We can reduce Au particles with uniform size through adjusting the PVP concentration.We produced supported ionic liquid catalysts on SBA-15 with plasma reduction for the first time. Dispersive Au nanoparticles on SBA-15 were formed after plasma reduction with [bmim][PF6] impregnated on the support. The particle sizes increased along with higher Au loading, up to 5%. Very few short nanowires could be found on the support. This was quite different from that without [bmim][PF6]. The Pd nanoparticles in supported ionic liquid catalysts produced after plasma reduction was also smaller than that without supported ionic liquid. XRD results confirmed that these nanoparticles were all face-centered cubic structures. Pd-[bmim][PF6]/SBA-15 catalysts showed good catalytic activities in Suzuki reactions. A series of catalysts were prepared with different precursors and ionic liquids impregnating sequences. Impregnating Pd(NO3)2 before ionic liquid [bmim][PF6], the catalyst prepared in this way showed the best activity.更多还原