Catalytic activity of platinum after exchange with surface active functional groups of carbon blacks

Abstract

The deposition of platinum on various carbon blacks has been carried out by forming active functional groups on the surface of the carbon support, and exchanging these active groups with different platinum complexes. Using H₂PtCl₆ solution, an aggregation rather than an exchange takes place. In this case, the anionic platinum complexes [PtCI₆]^2– involved have a tendency to form a coagulated platinum cluster after the reduction process. However, using ammonium platinum chloride, an exchange between the cationic platinum complexes and surface functional groups takes place. The exchange process involving the divalent platinum complex, [Pt(NH₃)₄]²⁺, is much faster than the one where the tetravalent platinum complex [Pt(NH₃)₆]⁴⁺, is involved. Transmission electron migrograph (TEM) photographs have shown that when using Pt(NH₃)₄Cl₂ solution for the exchange, platinum particles are extremely small (0.75–1.7 nm) and highly dispersed on the surface of the carbon black. A comparison of the catalytic activities of platinum supported on various carbon blacks was also carried out. The catalytic activity mainly depends on the particle size rather than the loading amount of the catalyst.