Molecular Metal Complex and Metal Cluster Catalysts on Supports: Organometallic Chemistry Meets Surface Science

Bruce Gates, University of California, California, USA


Industrial catalysts range from the simple—molecules in solution—to the complex—the heterogeneous surfaces of robust solids. The underlying sciences, organometallic chemistry and surface chemistry, are now merging as researchers succeed in synthesizing and characterizing molecular species on surfaces. The best understood of these supported catalysts are highly uniform, being isolated on regular (crystalline) supports such as zeolites. Syntheses of well-defined supported catalysts involve reactions of compounds such as Ir(C2H4)2(acetylacetonate) with support surface OH groups—to give structures such as Ir(C2H4)2, with the Ir atom bonded to two support oxygen atoms. Spectra, atomic-resolution electron microscopy images, and calculations at the level of density functional theory characterize the supported species and their bonding to the supports and demonstrate their high degrees of uniformity. Consequently, it is becoming evident how design these site-isolated catalysts—the design variables are the metal, the number of metal atoms in a catalytic site, the support, and other ligands bonded to the metal. We illustrate some supported molecular catalysts with appealing properties, such as stability at high temperatures and high selectivity for challenging reactions such as hydrogenation of 1,4-butadiene to give butenes.