Schwarzenegger Prize for Research

Thomas Do - Proton Assisted Reduction of CO₂ by Cobalt Pyridine Amino Macrocycles

2015 RESEARCH SYMPOSIUM, SECOND PRIZE

Project Summary: With the increasing amount of CO₂ in the atmosphere, the need to reduce it is rising. A popular solution is to convert CO₂ into liquid fuels, electrochemically. Our work consists of developing catalysts for the reduction of carbon dioxide into useful organic molecules that can be  converted to liquid    fuel.

Main Issue: Secondary sphere interactions, provided by built in proton relays in our catalyst trap reactive intermediates using hydrogen bonds and lower the energies associated with the reduction of CO₂. Various metal centers and functional groups will be chosen to in order to study the reactivity of the catalyst as well as its mechanism.

Learning Outcomes: I learned new synthesis and characterization techniques from making these catalysts. Aside from those, I also learned how to work in glove-boxes and how to use Schlenk-lines. In order to test our catalysts, I learned how to run electrochemical experiments.

Student Contribution: Participated in synthesis and characterization of macrocycles
Participated in electrochemical studies of macrocycles

Abstract: A series of amine bridged calix[4]pyridine cobalt complexes (CoPy₄(NR)₄²⁺, where R = H, Me, Allyl) were synthesized and studied for catalytic activity for the reduction of CO₂. Single Crystal X-Ray diffraction shows a saddle-like geometry, with the bridging amine groups pointing outwards. This geometry has been noted to be suitable for CO₂ reduction, because CO₂ is within hydrogen bonding distance from the amines. These secondary sphere elements are thought to stimulate enzyme like pendant proton relays to be used to capture CO₂ and assist with proton coupled electron transfer during its reduction.
These complexes were studied using cyclic voltammetry, under inert atmosphere and CO₂, in the presence and absence of protons. All complexes showed reactivity towards CO₂ reduction. CoPy₄(NH)₄²⁺ was determined to be the more active catalyst of the complexes, with bulk electrolysis showing a Faradaic Efficiency of ηCO= 100% ± 10% with high TOF. CoPy₄(NMe)₄²⁺ and CoPy₄(NAllyl)₄²⁺, however, were found to be less active towards CO₂ reduction.

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