Abstract

Optimization of hydride transfer (HT) catalysts to enhance rates and selectivities of (photo)electroreduction reactions could be a crucial component of a sustainable chemical industry. Here, we analyze how ring functionalization of the adsorbed transient intermediate 2-pyridinide (2-PyH*)—predicted to form in situ from pyridine (Py) in acidified water at a cathode surface and to be the key to selective CO2 photoelectroreduction on p-GaP—may enhance catalytic activity. Earlier studies revealed that 2-PyH*’s instability results from a protonation side reaction producing adsorbed dihydropyridine (DHP*), which is relatively HT-inactive. Reducing the electron density on 2-PyH* could limit this protonation, with the trade-off that it may become less active for HT from 2-PyH*–R to CO2. We explore here how Py functionalization affects the electron distribution and in turn tunes the catalytic performance of 2-PyH*. We indeed find that electron-withdrawing groups could enhance the stability of 2-PyH* by reducing its electron density on the ring. Furthermore, we find that the change in the number of electrons on the substituting group of the hydride donor is a good descriptor for both the stability against protonation and the magnitude of the HT barrier. We predict that –CH2–CH2F is the best candidate substituent, as it significantly improves the stability of 2-PyH* with only a small increase in HT barrier. –CH=CH2 and –CH2F also could be promising, although they require further investigation due to a larger HT-barrier increase.

Original languageEnglish (US)
Pages (from-to)22953-22958
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America
Volume116
Issue number46
DOIs
StatePublished - Nov 12 2019

All Science Journal Classification (ASJC) codes

  • General

Keywords

  • Carbon dioxide reduction
  • Catalyst functionalization
  • Hydride transfer

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