Cooperative and environmental effects in catalysts

Harold H. Kung

Chemical and Biological Engineering Department, Northwestern University, Evanston,
IL 60208-3120, USA

Abstract

In nature, enzymes function effectively under mild conditions of near neutral pH and room temperature using common organic functional groups such as amines, hydroxyls, and carboxylic acids, which, when used outside the enzyme environment, exhibit activities many orders of magnitude lower. It is understood that the enzyme protein provides an environment that is conducive to cooperative effect among the groups and hydrophobicity at the active center. In contrast, catalysis in abiotic systems seldom utilized such functions, especially heterogeneous catalysis. Instead, they rely on harsh reaction conditions of elevated temperatures and pressures, and/or strong acids and bases, with the consequence of sacrificing selectivity. Recently, advances in catalyst synthesis techniques make it increasingly possible to design and synthesize abiotic systems that possess multiple functionalities to achieve cooperative catalysis. Examples include cooperative acid-base catalysis in which a Lewis acid and a basic function are anchored on a silica surface, including SBA-15 and coordinated metal ions on the periphery of a dendrimer. We have investigated using nanocage structures to examine the effect of environment and discovered evidence of the “pKa shift” effect of amines groups inside the cage, primarily due to electrostatic repulsion. These and other examples will be discussed.

Speaker’s Bio - Dr. Kung is Professor at the Department of Chemical and Biological Engineering, and Director of the Center for Energy Efficient Transportation at Northwestern University. His research goal is to search for and develop the underlying chemical and engineering principles governing catalysis, especially regarding activity and product selectivity, and to make use of such knowledge to design novel and efficient catalysts and processes.