Organic Modification of Metals and Metal Oxides for Selective Catalysis

ABSTRACT

Composite inorganic materials are frequently used to catalyze large-scale industrial reactions. Identifying materials that are active and selective for specific reactions is important not only for making improvements to existing chemical processes but also for designing new routes to a sustainable energy economy. A common structure for solid catalysts is for metal nanoparticles—often considered the active component—to be dispersed onto high-surface-area metal oxides. However, it has become increasingly apparent that the role of the metal oxide can extend far beyond being a simple carrier for the metal nanoparticles; sites at the interface between the metal and metal oxide exhibit much faster rates for processes such as CO2 thermal reduction and upgrading of biomass-derived sugars. The chemistry at metal-metal oxide interfaces is often complex and poorly understood, and mechanisms for achieving additional control over catalyst performance are desired.

One alternative or complementary method for tailoring a catalytic interface is to modify the metal and/or oxide components with organic ligands. Such organic-modified materials can potentially be useful as technical catalysts, but they are especially valuable for controlled studies of reactivity at the interface between metal or metal oxide surfaces and a solvent or soft material. Such ligands in fact are widely employed as surfactants in the synthesis of metal nanoparticles. Numerous studies have shown that leaving these ligands in place can have beneficial effects on catalyst performance, especially related to selectivity toward desired products. Thus, one approach toward controlling selectivity in catalysis is to design these encapsulating ligands, as will be discussed in this presentation.

As an alternative to depositing organic monolayers on the metal nanoparticles, it is also possible to deposit them on the oxide support. As will be discussed here, support modification is especially attractive for reactions in which rates are dominated by sites at the metal–support interface. By varying the structure and chemical functionality of the organic ligands, one can hypothetically improve catalyst activity, selectivity, and stability in reactions such as CO2 hydrogenation and oxygenate hydrodeoxygenation. This presentation will describe the use of different components of the organic ligands—the “head” group that covalently attaches to the support and the “tail” organic function—to control selectivity in reactions at surfaces. It will also discuss the use of organic monolayers as precursors to well-defined (and more thermally stable) inorganic surfaces.

BIOGRAPHY

Will Medlin received his BS degree in chemical engineering from Clemson University. He received his PhD from the University of Delaware. After conducting postdoctoral research at Sandia National Laboratories in Livermore, California, he joined the faculty of the University of Colorado, where he now serves as Denver Business Challenge Endowed Professor in the Department of Chemical & Biological Engineering. His research focuses on the design of solid catalysts for energy and environmental applications. His work has emphasized catalyst surface modification using organic self-assembled monolayers or inorganic thin films to enhance control over catalyst surface and near-surface properties. Prof. Medlin has published approximately 160 peer-reviewed papers. He has received several research and teaching awards, such as the NSF CAREER and AIChE Himmelblau Awards. He has been a visiting professor at ETH-Zurich and the Chalmers University of Technology, is an Associate Editor for the journal Catalysis Science and Technology, and is the chair-elect of the ACS Catalysis division. He has also been active in producing educational tools for the widely used website learncheme.com.

http://www.colorado.edu/chbe/j-will-medlin