Institute of Chemistry, Carl von Ossietzky University Oldenburg;
Institute of Chemistry, Carl von Ossietzky University Oldenburg.
J Vis Exp. 2022 Jun 24(184). doi: 10.3791/63936.
Ligands like amines are used in the colloidal synthesis approach to protect platinum nanoparticles (Pt NP's) from agglomeration. Normally, ligands like amines are removed by diverse pre-treatment procedures before use in heterogeneous catalysis as amines are considered as a catalyst poison. However, a possible beneficial influence of these surface modifiers on hydrogenation reactions, which is known from spectator species on metal surfaces, is often neglected. Therefore, amine-stabilized Pt nanoparticles supported by titania (P25) were used without any pre-treatment in order to elucidate a possible influence of the ligand in liquid phase hydrogenation reactions. The catalytic activity of amine-stabilized Pt nanoparticles of two different sizes was investigated in a double-walled stirring tank reactor at 69 °C to 130 °C and 1 atm hydrogen pressure. The conversion of cyclohexene to cyclohexane was determined by gas chromatography (GC) and was compared to ligand-free Pt particles. All catalysts were checked before and after reaction by transmission electron spectroscopy (TEM) and X-ray photoelectron spectroscopy (XPS) for possible changes in size, shape, and ligand shell. The hydrogenation of cyclohexene in liquid phase revealed a higher conversion for amine-stabilized Pt nanoparticles on titania than the ligand-free particles. The hydrogenation of 5-methylfurfural (5-MF) was chosen for a further test reaction, since the hydrogenation of α, β-unsaturated aldehydes is more complex and exhibits various reaction paths. However, XPS and infrared spectroscopy (IR) proved that 5-MF acts as catalyst poison at the given reaction conditions.
配体如胺类物质被用于胶体合成方法中，以防止铂纳米颗粒（Pt NP）团聚。通常，在用于多相催化之前，需要通过各种预处理程序去除配体如胺类物质，因为胺类物质被认为是催化剂毒物。然而，从金属表面的 spectator 物种中可知，这些表面修饰剂对加氢反应可能有有益的影响，这一点常常被忽视。因此，未经任何预处理，就使用了由二氧化钛（P25）支撑的胺稳定的 Pt 纳米颗粒，以阐明配体在液相加氢反应中的可能影响。在 69°C 至 130°C 和 1 个大气压氢气压力的双壁搅拌槽反应器中，研究了两种不同尺寸的胺稳定 Pt 纳米颗粒的催化活性。通过气相色谱（GC）测定环己烯的转化率，并与无配体 Pt 颗粒进行比较。在反应前后，所有催化剂均通过透射电子显微镜（TEM）和 X 射线光电子能谱（XPS）进行检查，以检查尺寸、形状和配体壳是否发生变化。在液相中环己烯的加氢反应表明，与无配体的 Pt 颗粒相比，TiO2 上的胺稳定 Pt 纳米颗粒具有更高的转化率。选择 5-甲基糠醛（5-MF）作为进一步的测试反应，因为α，β-不饱和醛的加氢反应更复杂，并表现出各种反应途径。然而，XPS 和红外光谱（IR）证明，在给定的反应条件下，5-MF 是催化剂毒物。
