Highly Efficient and Selective Photocatalytic CO₂ Reduction to CO in Water by a Cobalt Porphyrin Molecular Catalyst

Abstract

The performance of a water-soluble cobalt porphyrin ([{meso-tetra­(4-sulfonatophenyl)­porphyrinato}­cobalt­(III)], CoTPPS) as a catalyst for the photoreduction of CO2 in fully aqueous media has been investigated under visible light irradiation using [Ru­(bpy)3]2+ as a photosensitizer and ascorbate as a sacrificial electron donor. CO is selectively produced (>82%) with high efficiency (926 TONCO; TONCO = turnover number for CO). Upon optimization, selectivities of at least 91% are achieved. Efficiencies up to 4000 TONCO and 2400 h–1 TOFCO (TOFCO = turnover frequency for CO) are reached at low catalyst loadings, albeit with loss in selectivity. This work successfully demonstrates the ability of CoTPPS to perform highly efficient photoreduction of CO2 in water while retaining its high selectivity for CO formation.

DFT and Empirical Considerations on Electrocatalytic Water/Carbon Dioxide Reduction by CoTMPyP in Neutral Aqueous Solutions**

“…Several previous publications have dealt with DFT studies of the electrochemical reduction of CO 2 using cobalt porphyrins, usually the simple cobalt porphine, as catalysts. [16,17,22,26] The mechanism has been investigated in aqueous acidic solutions and it was established that the catalytic cycles leading to carbon-based products involves decoupled and concerted proton-electron transfers. The present work exploits the solubility of CoTMPyP in aqueous solutions for experimental and computational examinations of its redox behavior in the absence and presence of CO 2 which were performed in H + ions-starving conditions (carbonate/bicarbonate buffer, pH 7).…”

“…Several cobalt porphyrins have been shown to be excellent catalysts for CO 2 RR by various theoretical and experimental investigations. [13][14][15][16][17][18] However, although solvation factors have been taken into account, theoretical calculations were made using the basic cobalt porphine. [13] In the present work we provide a combined experimental and theoretical analysis on the electrocatalytic capabilities of a water-soluble cobalt porphyrin, Cobalt [5,10,15,20-(tetra-Nmethyl-4-pyridyl) porphyrin] (CoTMPyP), in neutral aqueous solutions.…”

Recent Advances on Metalloporphyrin‐Based Materials for Visible‐Light‐Driven CO2 Reduction

“…[50] Among them, Ru complexes exhibit a broad absorption band located on 456 nm through the metal-to-ligand charge transfer. [51] Sakai and co-workers [52] utilized water-soluble cobalt porphyrin (CoTPPS) as catalyst and [Ru(bpy) 3 ] 2 + as photosensitizer for photocatalytic CO 2 reduction. The TON and turnover frequency (TOF) of the CO evolution reach 926 and 456 h À 1 , respectively, with high selectivity of 82 Sakai [53] and co-workers further explored the effects of peripheral groups in metalloporphyrin on CO 2 photoreduction.…”

“…When visible-light-driven CO 2 reduction is performed under monochrome LED (λ = 420 nm) using 1,3-dimethyl-2-phenyl-2,3-dihydro-1H-benzo[d]-imidazole (BIH) as electron donor and PhOH as proton source, [56] the TON of CO evolution exceeds 900, and the quantum yield is estimated to be 8 % Reprinted with permission. [52] Copyright 2019, American Chemical Society. (c) Molecular structures for CuPS, CoTPPS and CoTMPyP.…”

Highly Efficient Photoreduction of Low‐Concentration CO2to Syngas by Using a Polyoxometalates/RuIIComposite

“…[16] Ru II complexes (e.g.,e specially [Ru(bpy) 3 ]Cl 2 ,b py = bipyridine) with accessible redox states, high quantum efficiency, and long-lived excited states, are some of the most widely used metal complexes in CO 2 photoreduction. [17][18][19][20][21] The combination of thesec omplexes and semiconductors is considered as an efficient way to enhance photocatalytic reactivity and stabilityu nder visible-light irradiation. [22,23] Also, the heterogeneous process will facilitate catalystr e-use and liquid product separation.…”