Supercritical carbon dioxide as reaction medium: synthesis, catalytic properties and recovery of hybrids of amphiphilic macromolecules with metal nanoparticles

超临界流体表现出一系列不寻常的性质，可用于开发分离、化学反应或材料加工等领域的新反应。除了替代有毒工业溶剂的能力外，超临界流体的主要兴趣在于可以在压力和温度变化很小的情况下，连续调节从液体到气体的流体性质。目前，几纳米级的可溶过渡金属颗粒被认为在许多重要的合成转化反应中起着至关重要的作用。然而，它们的受控制备、稳定和催化反应后的回收仍然是关键挑战。在这项研究中，将制备金属纳米粒子，并将其稳定在两亲性大分子的极性超支化核心中。亲二氧化碳的壳层在超临界二氧化碳(ScCO2)中提供溶解性。通过直接在scCO2中合成来控制颗粒大小和形貌，以及作为一种替代方法在水介质中随后构建壳层，将被研究。研究了SCCO_2中双键加氢和C-C偶联(Heck反应)的催化性能，并与有机溶剂中的催化性能进行了比较。通过改变二氧化碳介质的性质，特别是密度，从催化反应的产物中回收亲二氧化碳的聚合物/纳米颗粒杂化材料将被研究。这对于催化活性纳米颗粒的回收特别有意义，因为对胶体稳定性施加的压力很小。

Supercritical fluids exhibit a range of unusual properties which can be exploited for the development of new reactions in such fields as separation, chemical reactivity, or material processing. Beyond the capability of replacing toxic industrial solvents, the main interest of supercritical fluids is the possibility to tune continuously the fluid properties from liquid to gas with small pressure and temperature variations. Soluble transition metal particles with sizes of a few nanometers are recognized today to possess a crucial role in many synthetically important transfomations. However, their controlled preparation, stabilization and recovery after catalytic reaction remain key challenges. In the research proposed metal nanoparticles will be prepared and stabilized in the polar hyperbranched core of amphiphilic macromolecules. A CO2-philic shell provides solubility in supercritical carbon dioxide (scCO2). Particle size and morphology control by synthesis directly in scCO2, and as an alternative approach in aqueous media with subsequent construction of the shell will be investigated. The catalytic properties in hydrogenation of double bonds and in C-C coupling (Heck reaction) will be studied in scCO2, and compared to catalysis in organic solvents. Recovery of the CO2-philic polymer/nanoparticle hybrides from the products of a catalytic reaction by means of changing the properties of the carbon dioxide medium, particularly the density, will be investigated. This is of particular interest with respect to the recovery of catalytically active nanoparticles, as little stress on colloidal stability is imposed.