Research
Research Group Goals
To enable transformative developments in sustainable catalytic processes, our goal is to engineer heterogeneous catalysts at the molecular level through a mechanistic understanding of the relationships between their synthesis, structure, and function for complex reaction chemistries . In particular, we are interested in the dynamic behavior of active sites and the impacts of their local microenvironments in porous materials.
Sustainability Applications
We aim to produce the renewable chemicals and fuels our society uses in daily life using renewable low-carbon feedstocks such as lignocellulosic biomass, earth’s most abundant organic carbon source.
We aim to catalytically mitigate the emissions of both greenhouse gases (N2O) and toxic gases (NOx) from automotive sources, particularly for next-generation renewable NH3 engines that could aid in decarbonizing heavy-duty transportation.
Some homogeneous transition metal catalysts are highly selective for industrial oxidation reactions (such as Wacker Oxidation over PdCu/zeolites), but involve the use of corrosive reagents and lead to the formation of toxic by-products. We aim to replace these processes with environmentally friendly heterogeneous catalysts where transition metal ions are instead stabilized by a solid catalyst support.
Renewable H2 from water electrolysis could be used for energy storage, transportation, and decarbonizing chemical production as part of the Renewable Hydrogen Economy. However, H2 is difficult to store and transport as a pressurized gas or cryogenic liquid. We are developing heterogeneous catalysts for the reversible storage of H2 in chemical bonds of Liquid Hydrogen Carriers (LHCs).
In collaboration with Profs Manos Mavrikakis, Jeff Greeley (UW-Madison) and Jennifer Lee (UC-Merced), we are investigating the kinetic consequences of dynamic restructuring of nanoparticle surfaces under reaction conditions. Figure: 10.1126/science.add0089.
Catalyst Design Toolkit
We synthesize porous materials with atomic-scale control of the structures of metal active sites, including both metal nanoparticles and metal cations, with an emphasis on metal-zeolite systems. Zeolites are crystalline materials made up of silica and alumina with well-ordered micropores that enable controlling both the diffusion of reacting molecules, and the structure and dynamics of intraporous metal site ensembles. We additionally use this platform to control the chemical and physical properties of the cavity surrounding active sites (i.e., their microenvironment).
We characterize these materials using a combination of active site titrations and spectroscopy, to understand the structures of their active sites and connect their structure to function. We are especially interested in how catalyst materials dynamically change under reaction conditions, probed by operando spectroscopy (spectroscopy during chemical reaction).
We use intrinsic reaction kinetics measurements to quantify catalyst performance, combined with advanced mechanistic tools (isolating reaction intermediates, isolating kinetic regimes, isotopic labeling, transient redox treatments) to elucidate reaction mechanisms.