Northwestern University Robert R. McCormick School of Engineering and Applied Science

Kung Research Group

Research: Catalysis

Catalytic reaction is an integral part of the large majority of environmentally friendly, energy- and material-efficient chemical and fuel production processes. To meet the challenges of continuously changing nature of feedstock and demand, new processes must be developed, and existing processes must be improved. The desired innovation can be assisted greatly by an adequate understanding of catalytic reactions and an ability to design catalytic centers. Our 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.

One emphasis is the design of novel catalytic structures with control of the nature of the active site and/or its environment, and developing methods to synthesize these structures. This is a nature-inspired approach, the goals of which include incorporating properties of enzymes, the natural catalysts, into nonbiological systems, controlling, manipulating, and utilizing confinement effects, and ultimately constructing catalysts on demand.

One example is the design and synthesis of nanometer-size macromolecular cages. Using micelles, dendrimers, and functionalized silsesquioxanes (POSS or spherosilicates) as templates, we have successfully created siloxane and carbosilane nanocages. The earlier structures contain one type of functional groups, such as amine. It was found that the amine groups interior to these cages exhibit unusual behavior, including large (~4 pH unit) pK shift in their protonation constant and higher activity and altered product selectivity in the decarboxylation of acetoacetone. Because these functional groups are inside the cages, the porous cage shell provides size selectivity to molecules that interact with these groups. Our second generation of nanocages has a core-shell structure in which the functional groups attached to the core and the shell is different.  Because of the limited number of carboxylic acid groups inside the cage, metal complexes of uncommon oxidation state can be generated, such as Co(I).

Another example is to use engineered structures to create mimic of metal-oxide support interface. A molecule that can be characterized in detail using solution techniques such as NMR is synthesized to possess multiple functional groups, some of which are designed to adsorb onto the metal particle, whereas others serve as the precursor to the oxide support mimic. An example is Ti(acac)- and amine-functionalized polymethylhydrosiloxane, which would adsorb onto Au particle surfaces and generate an Au-TiOx interface after oxidative activation. Such an interface has been found to be active in selective oxidation of propane to acetone using a mixture of oxygen and hydrogen gas