Homogeneous Photocatalytic Reduction of CO₂ to CO Using Iron(0) Porphyrin Catalysts: Mechanism and Intrinsic Limitations

Abstract

A photochemical catalytic reduction of CO2 was performed in an organic solvent with iron(0) porphyrins as homogeneous molecular catalysts under visible light irradiation. With modified tetraphenylporphyrins consisting of internal phenolic groups, the photochemical process led to the production of CO, with H2 as a minor product. High catalytic selectivity for CO formation and turnover numbers up to 30 were obtained. Degradation of the catalyst occurred at longer irradiation times, along with decreased selectivity. Furthermore, addition of a weak acid, which increased the reduction efficiency under electrochemical conditions, led to rapid deactivation of the catalyst. With the unmodified tetraphenylporphyrin as catalyst, we observed lower performance and higher proportion of H2, which highlighted differences in the reduction pathways followed. A combination of a spectroscopic study and product analysis performed under various conditions led to detailed reduction mechanisms and helped pave the way for designing durable photocatalytic systems.

Encapsulating Perovskite Quantum Dots in Iron‐Based Metal–Organic Frameworks (MOFs) for Efficient Photocatalytic CO2 Reduction

“…While PCN-221(Fe 0.2 )becomes amorphous ( Figure S7), indicating it totally decomposes after the photocatalytic reaction. [48] To identify the electron source for the reduction of CO 2 to CO and CH 4 ,the H 2 18 Oisotope trace experiment was carried out in aC O 2 -saturated ethyl acetate/H 2 18 Os olution containing MAPbI 3 @PCN-221(Fe 0.2 )p hotocatalyst, and the major mass spectrum signal with a m/z value of 36 ( 18 O 2 )c an be observed ( Figure S8). [48] To identify the electron source for the reduction of CO 2 to CO and CH 4 ,the H 2 18 Oisotope trace experiment was carried out in aC O 2 -saturated ethyl acetate/H 2 18 Os olution containing MAPbI 3 @PCN-221(Fe 0.2 )p hotocatalyst, and the major mass spectrum signal with a m/z value of 36 ( 18 O 2 )c an be observed ( Figure S8).…”

“…Thei mproved stability induced by the insertion of MAPbI 3 QDs into the pores of PCN-221(Fe 0.2 )m ay be attributed to the competitive light absorption between MAPbI 3 QDs and PCN-221(Fe 0.2 ), which can decrease the photodegradation of PCN-221(Fe 0.2 ). [48] To identify the electron source for the reduction of CO 2 to CO and CH 4 ,the H 2 18 Oisotope trace experiment was carried out in aC O 2 -saturated ethyl acetate/H 2 18 Os olution containing MAPbI 3 @PCN-221(Fe 0.2 )p hotocatalyst, and the major mass spectrum signal with a m/z value of 36 ( 18 O 2 )c an be observed ( Figure S8). In addition, the amount of oxygen generated in CO 2 -saturated ethyl acetate/water solution using MAPbI 3 @PCN-221(Fe 0.2 )a sap hotocatalyst is close to one fourth of total amount of electron consumption (e amount )f or the generation of CH 4 and CO ( Figure S9).…”

In‐Situ Synthesis of Tetraphenylporphyrin/Tungsten (VI) Oxide/Reduced Graphene Oxide (TPP/WO3/RGO) Nanocomposite for Visible Light Photocatalytic Degradation of Acid Blue 25

“…All the discernible peaks in the XRD of WO 3 (Figure ) were representative of the monoclinic phase (2θ=21.4, 32.8 and 57.4), orthorhombic phase (2θ=17.1, 39.8 and 49.4) and the hexagonal phase (2θ=12.9, 25, 27.2, 28.0, 37.8, 41.6, 43.4, 49.1, 52.2 and 60.4). The XRD pattern of TPP in the powder form (Figure ) shows multiple peaks with different intensities which indicates that the material is polycrystalline . The (002) reflections (2θ=26.9) corresponding to RGO is present with the intensity of the peak around 2θ=11 being absent which indicates that the prepared reduced graphene oxide (RGO) has little amount of various oxygen containing functionalities and intercalated molecules present as confirmed by the EDS and the FTIR results.…”

The concept of photochemical enzyme models – State of the art

“…Among the plethora of systems proposed for the photoreduction of CO 2 some remarkable examples combine controlled substrate binding and activation with highly selective product formation in a single light-responsive molecule acting both as a sensitizer and a catalyst [169][170][171]. These systems are promising candidates for the development of artificial carbon dioxide converting photoenzymes.…”

“…These systems are promising candidates for the development of artificial carbon dioxide converting photoenzymes. For example, an interesting Fe-based photocatalyst for the selective two-electron reduction of CO 2 into CO has been reported recently [171], which can be considered as a simple light-driven CO-dehydrogenase model. The receptor properties around the low-valent metal center are further assisted by additional hydrogen bonding motifs to stabilize the CO 2 substrate adduct formed.…”