Our research is focused on synthesizing, characterizing, and elucidating the properties of materials and catalysts that are relevant to chemical and energy conversion processes to improve energy and material conservation, and minimize impact on natural resources and the environment. The goal is to be able to use these materials to reduce energy demand of processes by lowering the activation barriers, improve product selectivity, enable development of processes that utilize sustainable resources, and remove contaminants from exhaust streams.
Our current research topics include:
1. Catalytic interfacial perimeter sites
Catalytic sites consisting of exposed atoms at the interface of the perimeter of a metal particle and the support oxide have been demonstrated to be the primary active sites in a number of reactions, such as selective oxidation of propane to acetone and dehydrogenation of 2-propanol on supported Au catalysts, water-gas shift, CO oxidation, hydrogenation of CO2 to methanol, and alcohol oxidation. Because these sites consist of two components (metal and oxide) of very different properties, they offer opportunities to tune the activities and selectivities of reactions in ways that are inaccessible by one component systems, thereby improving resource sustainability. In order to achieve this, it is necessary to fully elucidate the properties of these sites, especially the cooperative interaction of the two components and the structure, and develop a broad portfolio of synthetic protocols to access desired properties.
2. Alternate routes to generation of hydrogen peroxide in aqueous systems
Hydrogen peroxide is used to remove organic contaminants in aqueous streams. It is also an environmentally friendly oxidizing agent in the production of high value organic chemicals. However, it is currently produced by an energy intensive and environmentally unfriendly method. In situ generation of hydrogen peroxide by co-oxidizing water and dissolved organics would be a highly desirable approach since the hydrogen peroxide can be produced at the point of consumption, thus eliminating the energy penalty of purification and transportation. Although such a process has been reported in the literature, the process condition is not yet practical or has not achieved the goal of improving the environmental impact. We are working to understand the hydrogen peroxide formation mechanism and the catalyst requirement with an aim to improve these systems.
3. Selective catalytic transformation in complex systems
Reactions in complex systems are challenging but offer potential to access activities/selectivities that are otherwise not achievable. These systems may consist of complex reaction networks or catalysts. An example of the former is catalytic co-oxidation in which the catalyst is only active for one of the two reaction cycles. However, the reaction intermediates in the one catalytic cycle serve as intermediary that either initiate or catalyze the second cycle. The consequence is that the catalyst enables the second cycle to proceed without direct contact with any of its reactants, intermediates, or products. Such Noncontact Catalytic Systems is first discovered in our laboratory, and we are exploring its potential to improve sustainability in catalytic reactions.
An example of complex catalysts consists of active sites that involve multiple functionality at specific locations. Such systems have the potential to orient specific configurations of reactant/product molecules at the active site, enabling reactions of specific bonds and formation of target products to achieve region-selective and chemo-selective transformations. They also require rather high degrees of precision in the synthesis of active sites. We have been exploring using siloxane platforms to construct such catalytic systems due to the bond angle flexibilities of siloxanes and their chemical versatility. Thus far, we have constructed systems consisting of acid-base pairs, metal-siloxane structures that can be converted from being a Lewis acid to a Brønsted acid by adsorption of an alcohol, siloxane nanocages that impart a pK shift of about 4 pH units for the interior amine groups, and a carbosilane nanocage that stabilizes unusual Co(I) cations.
4. Antifouling surface structures
Fouling of heat exchange surfaces causes severe energy penalty to process heating systems. Recent computational results suggest that surfaces with hybrid structures could reduce fouling tendencies but also lower the heat transfer coefficient. Thus, there is an optimal structure where the energy efficiency gain from reduced fouling outweighs loss in heat transfer efficiencies, resulting in net energy saving. We are participating in a team effort to design and construct such nano-structured surfaces.