Abstract
Efficient reduction of CO2 into useful carbon resources particularly CO is an essential reaction for developing alternate sources of fuels and for reducing the greenhouse effect of CO2. The binuclear Ni, Fe−containing carbon monoxide dehydrogenase (CODHs) efficiently catalyzes the reduction of CO2 to CO. The location of Ni and Fe at proper positions allows their cooperation for CO2 to CO conversion through a push−pull mechanism. Bio−inspired from CODHs, we used several cofacial porphyrin dimers with different substituents as suitable ligands for holding two Fe ions with suitable Fe−Fe separation distance to efficiently and selectively promote CO2 to CO conversion with high turnover frequencies, TOFs. The substituents on the porphyrin rings greatly affect the catalysis process. By introducing electron-withdrawing/-donating groups, e.g. electron-withdrawing perfluorophenyl, at all meso positions of the porphyrin rings, the catalysis overpotential, η was minimized by ≈0.3 V compared to that obtained by introducing electron-donating mesityl groups. The Fe porphyrin dimers among reported catalysts are the most efficient ones for CO2 to CO conversion. Control experiments indicate that the high performance of the current CO2 to CO conversion catalysts is due to the presence of binuclear Fe centers at suitable Fe−Fe separation distance.
Highlights
Efficient reduction of CO2 into useful carbon resources CO is an essential reaction for developing alternate sources of fuels and for reducing the greenhouse effect of CO2
Six porphyrin dimer ligands linked by a 1,2-phenylene bridge and bearing different substituents at the porphyrin rings have been prepared according to stepwise methods outlined in Scheme S1 (SI)
In a DMF/0.1 M nBut4NPF6 solution saturated with Ar, the Fe porphyrin dimers (0.5 mM) and their corresponding Fe porphyrin monomers (1 mM) depict cyclic voltammetric (CV) behaviors shown in Figure S2 (SI) at a 50 mV/s scan rate
Summary
Efficient reduction of CO2 into useful carbon resources CO is an essential reaction for developing alternate sources of fuels and for reducing the greenhouse effect of CO2. The efficient reduction of CO2 into useful carbon resources CO is an essential reaction to overcome the limited supply of fossil fuels and the greenhouse effect of CO21–3. Fe porphyrin monomers have been reported to efficiently catalyze the electrochemical reduction of CO2 to CO in the presence of external or localized phenol as a weak proton donor to act as a proton relay during CO2 to CO conversion. Several anaerobic bacteria and archaea utilize Ni, Fe−containing carbon monoxide dehydrogenases (CODHs) with a [NiFe4S4] cluster at the active site as highly efficient catalyst for CO2 to CO conversion with high turnover frequency, TOF (12 s−1) at a low overpotential, η < 100 mV30–36. CO2 to CO conversion have been demonstrated with several binuclear- (e.g. Ni237–39, Cu240, Ir241, and Pd242) and polynuclear- (e.g. Ni343,44, Fe445, and iron-sulfur clusters; [Fe4S4(SR)4]2−, Ni− Fe4S4 and Co− Fe4S446–48) catalysts, with low TOF and/or high η-values
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