Hydrogen bonded pyridine dimer: A possible intermediate in the electrocatalytic reduction of carbon dioxide to methanol

Yong Yan, Jing Gu, Andrew B. Bocarsly

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20 Scopus citations

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.

Original languageEnglish (US)
Pages (from-to)515-521
Number of pages7
JournalAerosol and Air Quality Research
Volume14
Issue number2
DOIs
StatePublished - Mar 2014
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Environmental Chemistry
  • Pollution

Keywords

  • CO sequestration and conversion
  • Catalyst
  • Electrochemistry
  • Pyridinium

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