(547g) Metal Nanocatalysts, Their Synthesis and Size Dependent Covalent Bond Catalysis. Oxide‐Metal Interfaces As Active Sites for Acid-Base Catalysis

Colloidal chemistry is used to control the size, shape and composition of metal nanoparticles usually in the 1-­10 nm range. In-­situ methods are used to characterize the size, structure (electronic and atomic), bonding, composition and oxidation states under reaction conditions. These methods include sum frequency generation nonlinear optical spectroscopy (SFG), ambient pressure X�ray photoelectron spectroscopy (APXPS) and high pressure scanning tunneling microscope (STM). The catalytic behavior depends on the size, oxidation state, coordination number, crystallographic orientation of metal sites and bonding and orientation of surface adsorbates.

When metal nanoparticles are placed on different mezoporous or microporous oxide supports, the catalytic turnover rates and selectivities markedly change. The charge flow between the metal and the oxide ionizes the adsorbed molecules at the oxide-­metal interfaces and alters the catalytic chemistry (acid-­base catalysis).

The oxidation state of metal nanoparticles becomes less metallic and assumes higher oxidation states with decreasing size. The small nanoclusters behave similar to transition metal ions that are active homogeneous catalysts. Hybrid systems composed of enzymes, homogeneous and heterogeneous catalysts are constructed to study molecularly unified catalytic schemes for the future.