We examine a possible mechanism for the electrochemical reduction of carbon dioxide to carbon monoxide with cobalt salen complex, Co(salen), as the catalyst. Density functional theory was used to calculate the ground state energies and reaction energies of possible reaction intermediates. The results indicate that the reduction from [Co(salen)-CO2]- to Co(salen)-CO proceeds via a Co(salen)-COOH intermediate through a proton transfer and a subsequent concerted proton-electron transfer that releases one molecule of water. The catalyst is then regenerated after carbon monoxide dissociates from the complex.
}, url = {https://paperview.spp-online.org/proceedings/article/view/SPP-2018-PA-27}, author = {Meliton R. Chiong III and Francis N. C. Paraan} } @inproceedings {chiong, title = {Ab initio study on the binding of carbon dioxide to cobalt salen complex}, booktitle = {Proceedings of the 35th Samahang Pisika ng Pilipinas Physics Conference}, year = {2017}, month = {7{\textendash}10 June 2017}, pages = {SPP-2017-3B-05}, address = {Cebu City, Philippines}, abstract = {Metal-organic complexes, such as metal-Schiff bases, can function as catalysts for electrochemical reduction. In this work we present first principles electronic structure calculations for the adduct formation involving carbon dioxide (CO2) and cobalt salen [Co(salen)] complex. Binding energy calculations show that carbon dioxide forms a stable adduct with [Co(salen)]$^{-}$ complex. The bonding between carbon dioxide and the cobalt metal center involves back-bonding mainly between the metal dz2 orbital and the π* orbital of CO2. An accompanying partial charge transfer from Co to CO2 was observed. This study can be used as a preliminary result to further study the structure and stability of other cobalt-carbon complexes.}, url = {http://paperview.spp-online.org/proceedings/article/view/152}, author = {Meliton R. Chiong III and Francis N. C. Paraan} } @conference {chiong2017, title = {Ab initio study on the effects of phenyl substitution on the binding of carbon dioxide to salcomine}, year = {2017}, month = {24{\textendash}26 May 2017}, pages = {147}, publisher = {12th Siam Physics Congress}, address = {Rayong, Thailand}, abstract = {Metal-organic complexes, such as metal-porphyrins, can function as homogeneous catalysts for electrochemical reduction. In this work we present ab initio electronic structure calculations for a reaction involving carbon dioxide and salcomine, a coordination complex consisting of a salen ligand and a cobalt (II) atom. Changes to the binding energy due to substitutions on the phenyl ring by different functional groups are also studied. Cases where a shrinking HOMO-LUMO gap decreases the overpotential and increases the catalytic efficiency of the complex are analyzed. This study provides a theoretical basis for possible salen complex candidates as electrocatalyst for the reduction of carbon dioxide.}, url = {https://indico.cern.ch/event/486350/contributions/2493722/}, author = {Meliton R. Chiong III and Francis N. C. Paraan} } @conference {434, title = {A DFT-based determination of the mechanism of electrochemical reduction of CO$_{2}$ to CO by a cobalt-Schiff base catalyst}, year = {2017}, month = {8{\textendash}10 Nov 2017}, pages = {P024}, publisher = {9th Electronic Structure and Processes at Molecular-Based Interfaces Workshop}, address = {National University of Singapore, Singapore}, abstract = {We perform density functional theory (DFT) based calculations to investigate the reduction of carbon dioxide CO2 to carbon monixide CO using a cobalt-Schiff base catalyst, Co(salen). DFT calculated formation energies and reduction potentials showed that CO2 is reduced to CO via a [Co(salen)-COOH] intermediate. The first step of the mechanism involves the reduction of electrically neutral [Co(salen)]\ to [Co(salen)]-\ anion, followed by an electrophilic addition of CO2. Furthermore, the sigma bond formed between cobalt metal center and\ CO2\ involves a back-donation and partial charge transfer from cobalt to carbon. [Co(salen)-COOH] is further reduced to [Co(salen)-CO] and CO is released from the catalyst along with water H2O.
}, author = {Meliton R. Chiong III and Francis N. C. Paraan} }