Metal-Ligand Core-Shell Nanocomposite Catalysts for the Selective Semihydrogenation of Alkynes

摘要

In recent years, hybrid nanocomposites with core-shell structures have increasingly attracted enormous attention in many important research areas such as quantum dots, optical, magnetic, and electronic devices, and catalysts. In the catalytic applications of core-shell materials, core-metals having magnetic properties enable easy separation of the catalysts from the reaction mixtures by a magnet. The core-metals can also affect the active shell-metals, delivering significant improvements in their activities and selectivities. However, it is difficult for core-metals to act directly as the catalytic active species because they are entirely covered by the shell. Thus, few successful designs of core-shell nanocomposite catalysts having active metal species in the core have appeared to date. Recently, we have demonstrated the design of a core-shell catalyst consisting of active metal nanoparticles (NPs) in the core and closely assembled oxides with nano-gaps in the shell, allowing the access of substrates to the core-metal. The shell acted as a macro ligand (shell ligand) for the core-metal and the core-shell structure maximized the metal-ligand interaction (ligand effect), promoting highly selective reactions.' The design concept of core-shell catalysts having core-metal NPs with a shell ligand is highly useful for selective organic transformations owing to the ideal structure of these catalysts for maximizing the ligand effect, leading to superior catalytic performances compared to those of conventional supported metal NPs.