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Ayman Karim

RESEARCH


Karim's Group Research Overview:

The world's energy future depends on improving the efficiency of current energy conversion and storage systems and developing new processes for energy production from renewable sources. Designing more active, and especially more selective catalysts will define the role of catalysis in meeting our energy demand and lowering our dependence on fossil fuels.

The ultimate goal of my research group is to build a rational framework for the design of more active and selective catalysts by combining the synthesis of well-defined nanostructures with tunable geometric and electronic properties, detailed studies of reaction kinetics and following the catalyst dynamics under reaction conditions by in situ/operando characterization, including: X-ray Absorption Fine Structure Spectroscopy (XAFS), infrared spectroscopy, UV-Vis, small angle X-ray scattering (SAXS), calorimetry, transmission electron microscopy (TEM) and X-ray diffraction (XRD).


In my group there are currently three active research areas:

Atomic-scale view of nucleation and growth for controlled synthesis of metal nanoparticles:

Synthesis of nanoparticles with controlled size, shape and composition is a research area of great interest for several applications including electrocatalysis, photovoltaics, batteries, electronics, medicine and catalysis. While colloidal synthesis is one of the most promising, tunable methods for synthesizing nanoparticles of different sizes, shapes, and compositions, the overarching principles governing the nucleation and growth are still largely unknown and a trial-and-error approach is still often employed for the synthesis.

The focus of the work in this area is on combining microfluidics and in situ characterization tools to "image" the nucleation and growth of colloidal metal nanoparticles in solution and provide a fundamental understanding of their mechanisms with the goal to predict how to control the size and shape of colloidal metal nanoparticles.


Supported single-atom and subnanometer clusters for selective conversion of shale gas:
Shale gas production is expected to revolutionize the U.S. petrochemical industry and lower our dependence on imported oil. However, to replace petroleum for chemicals and fuels production, novel catalytic processes are required to utilize these abundant feedstocks. The major challenge lies in selectively activating and converting light alkanes, to olefins via dehydrogenation, or oxygenates (ex., alcohols, aldehydes, epoxides) via selective oxidation while avoiding complete dehydrogenation or complete combustion. Success in this arena could define the future of the energy and chemicals landscape in the U.S.

The work in this area is focused on studying the activation of alkanes on a unique class of supported single-atom and subnanometer clusters based on recent work in my group. The objective of the work is to provide a fundamental understanding of the correlation between the electronic properties of the single-atoms and subnanometer clusters and interaction with adsorbates with the reaction selectivity. The goal is use these insights and correlations to tune the electronic properties of the catalyst to design more active and selective catalysts.
Solvent-Catalyst Cooperative Effects in Heterogeneous Catalysis:
In heterogeneous catalysis, the solvent can affect the rate and selectivity of the catalyst. However, the origins of these effects are not well understood. Understanding the role of the solvent is particularly important in biomass conversion. It is important to understand the effect of the reaction medium on the kinetics for O-H, C-H, C-O and C-C bond scission in order to control the chain length and functional groups (alcohol, cyclic ether, acid, etc.) of the products.

The objective is to provide a fundamental understanding of the role of solvent in affecting the catalyst activity and selectivity with the goal to design better catalysts. The focus is on understanding the underlying mechanisms for the interactions between the solvent and catalyst surface using catalysts with well-defined nanostructures combined with advanced in situ / operando characterization methods capable of probing the solvent/surface as well as the solvent/adsorbates interactions.