Unconventional Noble Metal Nanoparticles with Enhanced Catalytic Properties: A Combined Experimental and Theoretical Study

University Of Texas At Austin, Austin TX

Investigators

Abstract

With support from the Macromolecular, Supramolecular and Nanochemistry program in the Division of Chemistry, the goal of this project is to prepare new metal nanoparticle catalysts for energy and environmental applications. Many large-scale catalytic processes are responsible for the formation of fuels, polymers and textiles, drugs and food additives, and are used in the remediation of toxins and environmental pollutants, and many of these require precious metal catalysts. Precious metals are both scarce and expensive. It is, therefore, of critical importance to find ways to prepare catalysts that require less precious metal, whilst maintaining the catalytic performance and also reducing the amount of waste by-products that are formed. Metal nanoparticles are discrete entities consisting of just a few hundred to a few thousand atoms. They might appear to be small fragments or as pieces "cut-away" from bulk metals. However, they are known to have properties that are superior to bulk metal, including enhanced catalytic behavior. For important chemical reactions that occur on metal surfaces, precious metal nanoparticles are very attractive because they have very large surface areas compared to their volumes, resulting in improved efficiency. In this project, the research groups of Dr. Simon Humphrey and Dr. Graeme Henkelman at the University of Texas at Austin are combining their expertise to prepare precious metal nanoparticles with previously unstudied structures, and to explain how the structures result in improved catalytic properties. A major goal of this research activity is to prepare nanoparticles based on mixtures of metals (alloys) that permits the dilution of very expensive metals with cheaper and more available metals, while also achieving improved catalytic properties. Another goal is to use microwave heating as a cheaper and faster way to prepare the nanoparticles. This project also incorporates important educational goals that are aimed at inspiring undergraduate students to actively participate in aspects of the research. A new microwave materials synthesis Freshman Research Initiative (FRI) stream is being introduced at the University of Texas - Austin, which enables undergraduates to engage in laboratory-based research, and promotes a deeper appreciation for scientific research. This is a collaborative project between a materials synthesis and catalysis group (Simon Humphrey) and a theoretical modeling group (Graeme Henkelman) at the University of Texas at Austin. The major objectives of this research activity are to synthesize metal nanoparticles (MNPs) with defined compositions, to test the MNPs in model catalytic reactions relating to industrially-relevant large-scale chemical transformations, and to use detailed and state-of-the-art theoretical approaches to gain a deep understanding of the relationships between surface reactivity and MNP structure. Experiment and theory are combined to elucidate general trends in reactivity as a direct function of composition; this ultimately provides important information that can be applied to direct the synthesis of other new MNPs with desired reactivity. The project features the preparation of a variety of novel metal nanoparticles (MNPs) using an innovative and technologically-relevant microwave-assisted method. Compared to classical methods, microwave-assisted synthesis allows for faster reaction times, easier scale-up, and can also allow access to products that cannot otherwise be obtained. Microwave heating is becoming popular in organic chemistry and the biosciences, but it has still yet to be fully exploited in materials and inorganic chemistry. In this project, microwave synthesis is exploited to gain access to MNPs with defined size and surface structure, and with unusual hybrid core-shell and alloy compositions. The surface chemistry of these previously unstudied MNPs are explored through model reaction studies including vapor- and liquid-phase reactions including hydrocarbon hydrogenation, carbonylation, and NOx reduction. Another goal of this project is the development of new theoretical approaches that can provide a more accurate description of surface reactivity than is presently available. This project also incorporates important educational goals that are aimed at inspiring undergraduate students to actively participate in aspects of the research. A new microwave materials synthesis Freshman Research Initiative (FRI) stream is being introduced at the University of Texas - Austin, which enables undergraduates to engage in laboratory-based research, and promotes a deeper appreciation for scientific research.