Selective Oxidation Reactions catalyzed by Metal Nanoparticles in Mesoporous Silica

我们的目的是在介孔二氧化硅中模板合成金属纳米团簇及其在CO和烯烃选择性氧化中的催化作用。介孔二氧化硅在催化方面的实际应用得到了广泛的探索。第一年，我们在介孔二氧化硅、FSM-16和MCM-41中合成了铂纳米颗粒。通过SEM和TEM等结构表征，证实颗粒位于内部孔隙中。以CO的优先氧化（PROX）为目标提纯聚合物电解质燃料电池（pefc）的H_2。我们发现Pt颗粒/FSM-16具有较高的CO转化率和选择性，并且在373 K以下具有良好的耐久性，而传统的二氧化硅或氧化铝负载Pt催化剂的活性和选择性较低。第二年，采用同位素标记法，利用红外光谱研究了PROX的反应机理。红外光谱结果表明，FSM-16的氧被用于CO氧化。我们提出支撑表面的活性OH基团攻击CO生成CO_2。水不是由H_2和O_2形成的，这是CO氧化具有高选择性的关键。即使Pt负载降低到0.5-1.0 wt%，通过优化空速，Pt/FSM-15催化剂的CO转化率也达到100%。我们还尝试了在介孔二氧化硅中使用Pt、Pd和Ag纳米颗粒选择性氧化乙烯。O_2转化率几乎为100%，但乙烯完全氧化为CO_2，没有生成环氧化物。因此，烯烃的选择性氧化需要辅催化剂来生成H_2O_2。

Our purpose is the template synthesis of metal nanoclusters in mesoporous silica and their catalyses in selective oxidation of CO and olefin. Mesoporous silicas have been extensively explored for practical applications in catalysis. In the first year, we synthesized platinum nanoparticles in mesoporous silicas, FSM-16 and MCM-41. By structural characterization such as SEM and TEM, it is confirmed that the particles are located in the internal pores. We targeted the preferential oxidation (PROX) of CO for the purification of H_2 for polymer electrolyte fuel cells (PEFCs). We found that Pt particle/FSM-16 provide high CO conversion and selectivity with good durability below 373 K, while conventional silica- or alumina- supported Pt catalysts showed low activity and selectivity. In the second year, the reaction mechanism of PROX was studied by infrared spectroscopy using the isotopic labeling method. The IR results suggest that oxygen of FSM-16 is used in the CO oxidation. We propose that active OH groups on the support surface attacks CO to give CO_2. Water is not formed from H_2 and O_2, which is a key to the high selectivity for CO oxidation. Even in the reduction of Pt loading as low as 0.5-1.0 wt%, Pt/FSM-15 catalyst showed 100%-conversion of CO by optimizing the space velocity. We also tried the selective oxidation of ethylene using Pt, Pd and Ag nanoparticles in mesoporous silica. The O_2 conversion was almost 100%, but ethylene is completely oxidized to CO_2 without the formation of epoxides. Therefore, it is suggested that co-catalysts are needed to generate H_2O_2 for the selective oxidation of olefin.