Colloids with controlled dimensions, morphology and composition can be used to obtain supported metal catalysts with desired characteristics. Yet, removal of capping agents which block active metal sites in such catalysts can be challenging: mild methods often result in incomplete removal of capping agents, whereas harsher methods can cause change in particle size or morphology or cause metal segregation for bimetallic particles. Here we provide evidence that polyvinylpyrrolidone used as a stabilizing agent for gold colloids is present both on the metal and the support surface after colloid deposition on the TiO₂ support. The polymer adsorbed on Au sites blocks their catalytic activity if it cannot be desorbed/decomposed under reaction conditions. Polyvinylpyrrolidone can be removed completely from the active gold surface of Au/TiO₂ without particle growth using a number of mild treatment methods described in this work, despite only partial removal (≈45 %) of the stabilizer from the bulk of Au/TiO₂ can be achieved. The remaining >50 % of polyvinylpyrrolidone resides exclusively on the TiO₂ support and has no effect on the optical properties and catalytic activity of gold nanoparticles. The treated catalysts demonstrate catalytic activity and selectivity similar to those of a catalyst prepared by impregnation. These findings are important for further advancing the preparation of well‐defined supported catalysts using metal colloids.

中文翻译：

---

胶体金催化剂的制备：从活性金位点选择性去除聚乙烯吡咯烷酮


具有受控尺寸、形态和组成的胶体可用于获得具有所需特性的负载金属催化剂。然而，去除封闭此类催化剂中活性金属位点的封端剂可能具有挑战性：温和的方法通常会导致封端剂的不完全去除，而较严厉的方法可能会导致颗粒尺寸或形态的变化或导致双金属颗粒的金属偏析。在这里，我们提供的证据表明，在 TiO ₂载体上胶体沉积后，用作金胶体稳定剂的聚乙烯吡咯烷酮同时存在于金属和载体表面上。吸附在金位点上的聚合物如果在反应条件下不能解吸/分解，就会阻碍其催化活性。使用本工作中描述的许多温和处理方法，可以从 Au/TiO ₂的活性金表面完全去除聚乙烯吡咯烷酮，而无需颗粒生长，尽管稳定剂仅从 Au/TiO ₂本体中部分去除（约 45%）可以实现。剩余>50%的聚乙烯吡咯烷酮仅存在于TiO ₂载体上并且对金纳米粒子的光学性质和催化活性没有影响。处理过的催化剂表现出与浸渍制备的催化剂相似的催化活性和选择性。这些发现对于进一步推进使用金属胶体制备明确的负载型催化剂非常重要。