Immobilized Zinc Complexes for Dilute CO2 Capture

University Of Louisville Research Foundation Inc, Louisville KY

Investigators

Abstract

With the support of the Chemical Mechanism, Function, and Properties Program of the Division of Chemistry, Professor Craig Grapperhaus of the Department of Chemistry and Professor Gautam Gupta of the Department of Chemical Engineering at the University of Louisville are developing immobilized zinc complexes for the reversible binding of carbon dioxide. The goal of this research is to understand the fundamental molecular mechanisms of carbon dioxide binding and release, with the longer-term potential for capturing carbon dioxide from dilute sources for delivery as a production feedstock for applications that currently require concentrated, high purity carbon dioxide. The fundamental studies include two different strategies to immobilize zinc complexes on solid substrates, materials characterization, and measuring the effects of immobilization on the electronic structure and acid/base properties of the complexes. Evaluation of carbon dioxide capture and release includes optimizing reaction conditions, confirming product identities, and quantifying equilibrium binding constants and loading capacities. Broader impacts include the improved molecular-level understanding of carbon dioxide interactions with small molecule metal complexes, workforce development at the interface of chemistry and chemical engineering, and curriculum development. The reversible capture of carbon dioxide from dilute sources is a critical challenge to collect and deliver this ubiquitous but gaseous carbon feedstock for use in catalytic reactions and other applications requiring high purity, concentrated carbon dioxide. A key innovation in the proposed work is the use of metal-ligand cooperativity in complexes with a Lewis acidic metal center and non-coordinating Lewis base in close proximity. The Lewis acid-base pair facilitates carbon dioxide capture via insertion into a metal-alcohol bond, which balances the thermodynamics to provide for facile capture and release. Immobilization of the complexes on solid substrates will allow translation of the homogeneous, solution reactivity to heterogeneous conditions. A major advantage of this approach is that a large number of active sites can be incorporated per volume of material to increase the carbon dioxide capacity. Immobilization will be achieved through chemisorption via axial ligand exchange and/or covalent bonding via chelate functionalization. The reversibility of the carbon dioxide capture/release process will be demonstrated using pressure swing adsorption, which avoids the heating employed for many other carbon dioxide capture systems. This may improve durability and will reduce energy consumption during the release process. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.