Homogeneous Reduction of CO2 by Photogenerated Pyridinyl Radicals

作者：Riboni Francesca; Selli Elena; Hoffmann M R; Colussi A J^*

来源：Journal of Physical Chemistry A, 2015, 119(19): 4433-4438.

DOI：10.1021/jp509735z

We report that 1-hydropyridinyl radical (1-PyH center dot) photogenerated in solution react with dissolved CO2 en route to its 2e(-) reduction into carboxylic acids. The 254 nm excitation of pyridine (Py) in deaerated 2-PrOH/H2O Mixtures saturated with 1 atm of CO2 yields a suite of products, among which we identified Na(HCOO)(2)(-) (m/z(-) = 113), C5H6NCOO- (m/z(-) = 124), and C5H10O2NCOO- (m/z(-) = 160) species, by electrospray ionization, mass spectrometry. These products demonstrably contain carboxylate functionalities that split CO2 neutrals via collisionally induced dissociation. We infer that 1-PyH center dot [from (1) Py-3* + 2-PrOH -> 1-PyH center dot + (PrOH)-Pr-center dot] adds to CO2, in competition with radical-radial reactions, leading to intermediates that are in turn reduced by (PrOH)-Pr-center dot into the observed species. The formation of carboxylates in this system, which is shown to require CO2, Py, 2-PrOH, and actinic radiation, amounts to the homogeneous 2e(-) reduction of CO2 by 2-PrOH initiated by Py*. We evaluate a rate constant (2) k(2)(1-PyH center dot + CO2 -> Py-center dot-1-COOH) approximate to O (10) M-1 s(-1) and an activation energy E-2 >= 9 kcal mol(-1) that are compatible with thermochemical estimates for this reaction.

• 出版日期2015-5-14