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首页> 外文学位 >Preparation, characterization and kinetic evaluation of silica supported dendrimer-derived platinum/ruthenium catalysts.
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Preparation, characterization and kinetic evaluation of silica supported dendrimer-derived platinum/ruthenium catalysts.

机译：二氧化硅负载的树枝状聚合物衍生的铂/钌催化剂的制备，表征和动力学评估。

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Bimetallic catalysts can often provide enhanced selectivity, stability, and/or activity, and are typically prepared by either co-impregnation or successive impregnation of both metal salts onto the catalyst support. A complex mixture of bimetallic and monometallic nanoparticles often occurs, resulting in poor control over catalyst performance and hindering development of structure-performance relationships. Dendrimer-metal nanocomposites (DMN) provide a novel synthetic route that can been used to produce heterogeneous catalysts. Dendrimers are mono-disperse hyper-branched polymers, whose internal functional groups can coordinate with transition metal ions (e.g., Pt2+, Ru 3+). The resulting complexes can be reduced to form encapsulated metal nanoparticles and/or clusters, which can then be introduced onto high surface area oxide supports. Upon removal of the dendrimer "shell", enhanced control over supported nanoparticles can be achieved.;In this work, both the delivery of the DMNs to the support and the synthesis of catalysts have been investigated. A series of Pt, Ru and Pt-Ru catalysts supported on silica has been synthesized using G4OH PAMAM dendrimer. The dendrimer-derived bimetallic catalysts were prepared by both co- and sequential complexation of the metal salts. They have been characterized by several techniques, including high resolution transmission electron microscopy (HRTEM), Fourier transform infrared spectroscopy (FTIR), temperature programmed (TP) titration and X-ray diffraction (XRD). Furthermore, liquid phase selective hydrogenation of 3,4-epoxy-1-butene (EpB) was used as probe reaction to evaluate their catalytic performance.;The dendrimer-derived PtRu bimetallic catalyst prepared by the co-complexation method exhibits a superior catalytic activity among all the three bimetallic catalysts, followed by sequential complexation catalyst, and finally the conventional catalyst. With these catalysts, the turnover frequency (TOF) changes by over a factor of five. Comparison of these activities to those predicted by using TOF of monometallic Pt or Ru sites suggests that there must be some type of new bimetallic site created. This hypothesis is supported experimentally by the XRD studies, where the Ru contents in the PtRu alloy phases can be correlated linearly with the corresponding catalytic activities. In addition, the reaction pathway on co-complexation catalyst has been changed toward crotonaldehyde intermediate as opposite to 3-buten-1-ol. This change can also be attributed to the dual PtRu sites, which exhibit different crotonaldehyde adsorption capacities.
机译：双金属催化剂通常可以提供增强的选择性，稳定性和/或活性，并且通常通过将两种金属盐共浸渍或相继浸渍到催化剂载体上来制备。双金属和单金属纳米粒子的复杂混合物经常出现，导致对催化剂性能的控制不良，并阻碍了结构-性能关系的发展。树枝状金属纳米复合材料（DMN）提供了一种新颖的合成路线，可用于生产非均相催化剂。树枝状聚合物是单分散的超支化聚合物，其内部官能团可以与过渡金属离子（例如Pt2 +，Ru 3+）配位。可以还原所得的络合物以形成包封的金属纳米颗粒和/或簇，然后可以将其引入高表面积的氧化物载体上。去除树枝状聚合物“壳”后，可以实现对负载型纳米颗粒的增强控制。在这项工作中，已经研究了DMNs向载体的传递和催化剂的合成。使用G4OH PAMAM树枝状大分子合成了一系列负载在二氧化硅上的Pt，Ru和Pt-Ru催化剂。树枝状聚合物衍生的双金属催化剂是通过金属盐的共配和顺序配位制备的。它们具有多种技术的特征，包括高分辨率透射电子显微镜（HRTEM），傅立叶变换红外光谱（FTIR），程序升温（TP）滴定和X射线衍射（XRD）。此外，以液相选择性氢化3,4-环氧-1-丁烯（EpB）为探针反应来评价其催化性能。通过共络合法制备的由树枝状聚合物衍生的PtRu双金属催化剂表现出优异的催化活性。在所有三种双金属催化剂中，依次是顺序络合催化剂，最后是常规催化剂。使用这些催化剂，周转频率（TOF）变化超过5倍。将这些活动与通过使用单金属Pt或Ru位置的TOF预测的活动进行比较，表明必须创建某种新的双金属位置。 XRD研究通过实验支持了这一假设，其中PtRu合金相中的Ru含量可以与相应的催化活性线性相关。另外，与3-丁烯-1-醇相反，共络合催化剂上的反应途径已向巴豆醛中间体改变。这种变化也可以归因于两个PtRu位点，它们显示出不同的巴豆醛吸附能力。

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