Surface-Mediated Design and Catalytic Properties of Active Metal Complexes for Advanced Catalysis Creation

Abstract

Molecular-scale design of catalytically active structures at oxide surfaces is highlighted, focusing on our recent challenges for selective heterogeneous catalysis. We found novel structural transformations of supported metal complexes on oxide surfaces and achieved unique selective catalysis for various chemical syntheses. In this account, the advanced design of supported metal-complex catalysts on oxide surfaces and the in situ characterization of their structural kinetics, which means kinetics of structural changes of catalysts themselves, under catalyst-working conditions are reviewed. Surface-Mediated Design of Catalytically ActiveStructures for Selective Catalysis 1.1 Introduction: Metal-Complex Attaching on Oxide Surfaces. Heterogeneous solid catalysts have been widely utilized for the industrial production of many synthetic chemicals. The advantages of heterogeneous catalysts are not only the separation of catalysts and products from reaction media but also their high durability and catalytic activities resulting from the unique structures of catalytically active sites at solid surfaces. Relationships among the metal structures, organized environment, and the catalytic properties of surface species tell us the nature of catalysis and new strategy for rational design of heterogeneous catalysts.Metal-complex attachment to oxide surfaces is a practical way to produce molecularly regulated structures of active metal species on oxide surfaces, and subsequent structural transformation in a controllable manner often provides unique regulated metal structures active for selective catalytic reactions. 116 There are several types of metal-complex attachment techniques: coordination of metal-complex precursors to immobilized ligands on organic polymers, 1721 coordination of metal-complex precursors to functional ligands bound to oxide surfaces, 2,4,2225 intercalation into clay materials, 26 ion exchange into porous materials such as zeolite and mesoporous silica, 27 and direct attachment of metal-complex precursor onto oxide surfaces. 3,6,11,28,29 The interfacial attachment between a metal complex and an oxide surface can produce unique metal coordination different from the original metal-complex precursor. For example, SiOH is reacted with a M(CH 3 ) complex and a M(OSi) complex is produced, releasing CH 4 . A chemical bond between a metal-complex precursor and a support surface modifies the reactivity of the supported metal complex, resulting in novel catalytic activity the precursor complex does not exhibit. 3,6,11,28,29 Traditional ion-exchange on zeolites and intercalation to clay materials are also typical ways to introduce metal species onto solid supports although the valences and types of metal precursors are restricted. 4 Direct reactions of metal-complex precursors and hydroxy groups on oxide surfaces create novel metal-coordination structures, and many important factors for selective catalysis can be controlled at the interface, such as electronic properties and coordination sphere of the attached metal...