Representative Research Areas
Molecular Catalysts for Renewable Fuels: Electrochemical and Light-Driven Carbon Dioxide Reduction
Economic growth and an increasing global population continue to drive worldwide energy consumption to new heights. This energy is largely sourced from fossil fuels, whose combustion releases greenhouse gases that contribute to climate change and other environmental concerns. Carbon dioxide is the chief component of this waste stream and a readily accessible C1 building block for generating value-added products. In this context, the catalytic conversion of carbon dioxide (CO2) and water (H2O) into chemical fuels, such as methane, using solar energy or renewable electricity is an attractive strategy. By recycling CO2 back into renewable fuels or commodity chemicals, net carbon emissions can be reduced and an underutilized resource can be tapped into.
To effectively utilize CO2, better catalysts are needed to mediate its multielectron conversion. However, CO2 is relatively inert and very negative voltages or strong chemical reductants are common for its conversion. An additional challenge lies in achieving this reaction in water where aqueous protons are utilized selectively for CO2 reduction rather than hydrogen generation. Our strategy for CO2-to-fuel conversion involves the rational design of homogeneous catalysts with redox-active and/or dinucleating ligands, which enable access to multiple reducing equivalents at modest potentials and cooperative modes of CO2 activation, respectively. Second-coordination sphere functionality will also be incorporated to stabilize intermediates and enhance reactivity.
Water Oxidation and Hydrocarbon Functionalization with Robust Metal-Oxo Catalysts
High-valent metal-oxo species are potent oxidants in chemistry and biology for a variety of reactions, including the oxidation of water and hydrocarbons. Water oxidation is the oxidative half reaction in nearly all schemes for artificial photosynthesis. The decomposition of H2O to O2 supplies the protons and electrons needed in reductive half reactions that convert and store solar energy in the form of chemical bonds. Belying the structural simplicity of the starting material and product, water oxidation is a demanding multi-electron/multi-proton reaction. A lack of efficient and earth-abundant catalysts for water oxidation has been a bottleneck to solar fuels.
Likewise, hydrocarbon oxidation is an important class of reactions with the potential to streamline organic synthesis. Raw chemical feedstocks, such as petroleum and natural gas, are primary sources of inexpensive hydrocarbons for the chemical and pharmaceutical industries. However, they have thermodynamically stable, kinetically inert C−H bonds that are not often viewed as chemical handles for further manipulation. A challenge lies in converting these readily available feedstocks into versatile organic building blocks in a mild and atom economical manner. Circuitous synthetic routes engrossed in the maintenance and interconversion of functional groups throughout a reaction sequence can be avoided with catalysts capable of selective C−H bond functionalization.
Despite the remarkable progress that has been made to demonstrate the scope of chemistry available to synthetic metal-oxo catalysts, significant improvements in catalyst activity, selectivity, and stability are needed to realize the full potential of these systems. To overcome these limitations, we aim to develop new mononuclear and dinuclear metal-oxo catalysts with oxidatively-rugged ligands that enforce more reactive structures.
Bioinspired Chemistry on Surfaces
Nature tightly regulates the environment around metalloenzyme active sites to achieve catalysis with high efficiency and selectivity. This environment, comprised of specific noncovalent interactions such as hydrogen bonding, is referred to as the second-coordination sphere and plays a key role in orchestrating reactivity at the first-coordination sphere. We seek to mimic this concept on electrode surfaces to develop scalable catalytic systems to manage proton inventories, stabilize intermediates, and direct reaction pathways.