Polymers are irreplaceable in the global economy, with myriad uses in packaging, construction, transportation, electronics, and healthcare industries. However, their massive-scale manufacture, single-use function, long lifetimes, slow decomposition rates, and disruption of sensitive ecosystems have created a crisis of plastics waste. Unfortunately, conventional mechanical recycling methods are limited by considerable technological and economic challenges. Chemical upcycling, an emerging alternative to the classical recycling approach, would use plastic waste as a feedstock to synthesize value-added chemicals and materials. This project focuses on developing advanced catalysts that can achieve efficient and selective upcycling of waste plastics to high-value chemicals.

Precious metals and metal alloys are important heterogeneous catalysts for renewable energy and materials. However, both of them have their limitations. Precious metals have low natural abundance and are expensive. Metal alloys have unstable surfaces due to surface segregation under reaction conditions, which renders the identification of active sites and the understanding of reaction mechanisms difficult. My research group will address these limitations by developing new intermetallic NP catalysts. Intermetallic compounds, which consist of two or more metallic elements, adopt specific crystal structures as well as electronic structures different from the constituent elements. The modified electronic structures of intermetallic compounds make them unique catalytic materials. It has been proposed that such compounds should be treated as new “elements” considering their potential in catalysis. The inherent properties of intermetallic compounds, stable and exhibit a large variety of structures, will help us to discover catalysts with stable surfaces, consisting of more abundant metals, to replace unstable alloy and precious metal catalysts.

Metal-organic frameworks (MOFs) are unique support materials for metal nanoclusters (NCs) that have great potential due to their structural diversity, flexibility, tailorability, and high porosity. A wide spectrum of applications for MOF-based materials have been demonstrated in gas storage, chemical adsorption and separations, catalysis, sensors, and drug delivery. Metal NCs and nanoparticles supported on MOFs have been used as heterogeneous catalysts in many reactions, such as hydrogenation, oxidation, and carbon-carbon bond coupling. However, the diameters of most of these NCs and nanoparticles are larger than the cavities of the MOFs, which indicate that the nanoparticles are mostly supported on the external surface of the MOFs. To fully utilize the benefit of the geometrically and chemically uniform cavities of MOFs, we need to fully confine the catalytic NCs inside the cavities of MOFs. With NCs confined inside the cavities of MOFs, we could fully realize the benefit to have MOFs as supports for metal NC catalysts.

The goal of this research is to develop low cost catalysts based on graphene-derived nanomaterials and use them to improve the efficiency of several key steps in biomass refinery. To make the cost of biomass derived fuels comparable or lower than that of petroleum fuels, it is necessary to develop new catalysts and processes that can substantially improve the efficiency of biomass refinery. Two attractive biomass refinery processes, pyrolysis and hydrolysis of lignocellulose, usually give molecules containing high oxygen content, and thus low energy density to be used directly as fuel. Therefore, upgrading of the lignocellulose derived oxygenates is necessary for them to be fit in appropriated fuel classes (i.e., gasoline, diesel, or jet fuels). The general approaches for upgrading the oxygenates are to decrease their oxygen content, and to build carbon-carbon bonds, targeting different fuel classes. Catalysts play a vital role in converting and upgrading biomass to fuels, and thus need to be studied extensively. Catalysts based on graphene-derived nanomaterials could greatly improve the efficiency of biomass conversion to liquid fuels, but they need to be systematically explored for this purpose. These improvements will substantially decrease the cost of biomass conversion.