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Hydrogen Bonded Pyridine Dimer: A Possible Intermediate in the Electrocatalytic Reduction of Carbon Dioxide to Methanol

Author(s): Yan, Yong; Gu, Jing; Bocarsly, Andrew B

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Abstract: Previously, electrogenerated pyridinyl was implicated as a catalyst for the reduction of CO2 to methanol. However, recent quantum mechanical calculations of both the homogeneous redox potential for the pyridinium/pyridinyl redox couple (900 mV more negative than experimentally reported) and the pKa of the reduced pyridinyl species (~27) have led to the proposal that the homogeneous reduction of pyridinium does not play a role in the observed catalytic reduction of CO2 to methanol. In contrast, a more complete consideration of the reaction including the realization that pyridinium reduction is tightly coupled to H2 evolution, produces a calculated redox potential in agreement with the experimental findings. In reexamining this system, it is found that aqueous solutions containing a near equimolar mixture of pyridine and pyridinium (i.e., solution pH near the pyridinium pKa = 5.2) contain a substantial concentration of a hydrogen-bonded dimer formed by the generation of a N-H•••N bond containing one strong NH bond and one elongated NH bond. This species has been identified by X-ray diffraction of crystals grown in aqueous media from pyridine/pyridinium mixtures, and can be observed directly in solution using Raman spectroscopy. DFT (density functional theory) calculations indicate that the pKa for this species is ~22, a value that is consistent with a proton exchange capability. This suggests that this hydrogen bonded dimer may be the pre-electrocatalyst for the observed activation of CO2.
Publication Date: 26-Feb-2010
Electronic Publication Date: 2014
Citation: Yan, Yong, Gu, Jing, Bocarsly, Andrew B. (2014). Hydrogen Bonded Pyridine Dimer: A Possible Intermediate in the Electrocatalytic Reduction of Carbon Dioxide to Methanol. Aerosol and Air Quality Research, 14 (2), 515 - 521. doi:10.4209/aaqr.2013.06.0227
DOI: doi:10.4209/aaqr.2013.06.0227
ISSN: 1680-8584
EISSN: 2071-1409
Pages: 515 - 521
Language: en
Type of Material: Journal Article
Journal/Proceeding Title: Aerosol and Air Quality Research
Version: Final published version. This is an open access article.

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