Visible light-induced photocatalytic CO2 reduction reaction (CO2RR) is a feasible and promising option to tackle the greenhouse effect and energy crisis. Herein, two ferric porphyrin-based porous organic polymer semiconductors, hereafter referred to as POPn-Fe (porous organic polymers, n = 1 or 2, corresponding to a benzene/biphenyl unit as a linker between porphyrin units), are synthesized for the visible light-driven CO2RR to produce syngas. The CO/H2 evolution rates for POP2-Fe under irradiation >420 nm are found to successfully reach up to 3043 and 3753 μmol g–1 h–1, respectively. Interestingly, the experiment results imply that the ferric porphyrin site could be responsible for CO evolution and the uncoordinated porphyrin unit in POPn or POPn-Fe semiconductors may be obligate for H2 formation. Furthermore, as evidenced by Mott–Schottky plots, the extended π-conjugation with the biphenyl linker makes POP2-Fe a lower conduction band potential, which helps the ferric porphyrin sites capture electrons from the photosensitizer, thus producing more CO to realize selectivity control. Also, the efficient catalytic activity of POP2-Fe is presumably attributed to the accelerated charge transfer as well as facilitates photogenerated electron and hole separation. This work offers an elegant strategy to design and optimize earth-abundant metal visible light photocatalysis for CO2 reduction to syngas with CO/H2 ratio control.
Carbon dioxide (CO2) is the major greenhouse gas and also an abundant and renewable carbon resource. Therefore, its chemical conversion and utilization are of great attraction for sustainable development. Especially, reductive conversion of CO2 with energy input has become a current hotspot due to its ability to access fuels and various important chemicals. Nowadays, the controllable CO2 hydrogenation to formic acid and alcohols using sustainable H2 resources has been regarded as an appealing solution to hydrogen storage and CO2 accumulation. In addition, photocatalytic CO2 reduction to CO also provides a potential way to utilize this greenhouse gas efficiently. Besides direct CO2 hydrogenation, CO2 reductive functionalization integrates CO2 reduction with subsequent C–X (X = N, S, C, O) bond formation and indirect transformation strategies, enlarging the diverse products derived from CO2 and promoting CO2 reductive conversion into a new stage. In this Perspective, the progress and challenges of CO2 reductive conversion, including hydrogenation, reductive functionalization, photocatalytic reduction, and photocatalytic reductive functionalization are summarized and discussed along with the key issues and future trends/directions in this field. We hope this Perspective can evoke intense interest and inspire much innovation in the promise of CO2 valorization.
Capturing CO2 and subsequently converting into valuable chemicals has attracted extensive attention. Herein, a series of biomass‐based N‐rich porous carbon materials with high specific surface area and pore volume were prepared using biomass waste soybean dregs as precursors. The nitrogen content was up to 4 % with different forms in the carbon skeleton such as pyridine‐N, pyrrole‐N. The synergistic effect of ultra‐micropore (pore size <0.7 nm) and N‐containing groups endowed the materials with a high CO2 adsorption capacity, reaching 6.3 and 3.6 mmol g−1 at 0 and 25 °C under atmospheric pressure, respectively. In addition, the sufficient interaction between N‐containing groups and CO2 was demonstrated by solid‐state nuclear magnetic resonance spectroscopy, and the captured CO2 was possibly activated in the form of carbamate, which is conducive to subsequent conversion. Therefore, the supported catalyst with the as‐synthetic porous carbon material as the carrier and ZnII as catalytic sites was prepared and successfully applied for carboxylative cyclization of propargylic amine with CO2 to afford the 3‐benzyl‐5‐methyleneoxazolidin‐2‐one. The results showed that CO2 capture and in‐situ conversion work effectively to produce highly value‐added chemicals. In this process, the captured CO2 could be activated and fixed into chemicals in mild conditions. More importantly, the energy consumption in CO2 desorption and adsorbent regeneration could be avoided. The valorization of both solid waste and CO2 to valuable chemicals provides an elegant strategy of killing three birds with one stone.
The development of efficient catalysts for the alkylation of amines with carboxylic acids is attracting much attention. Herein, we would like to report an earthabundant iron-catalyzed protocol for the N-alkylation of anilines using carboxylic acid as alkyl source and phenylsilane as reducing agent. With Fe 2 (CO) 9 as a catalyst, a broad range of primary and secondary anilines are successfully converted to the corresponding tertiary anilines. Furthermore, this N-alkylation mainly goes through the amide pathway; while the aldehyde pathway can not be ruled out.
New rhenium bipyridyl complexes with dipyrromethene-BF 2 chromophores (A-ReBDP-CZ, A-ReBDP 2 , ReBDP-CZ, and ReBDP 2 ) were developed for highly efficient photocatalytic carbon dioxide (CO 2 ) reduction to carbon monoxide (CO). These catalysts consisted of two moderate electron-deficient groups (dipyrromethene-BF 2 , BDP) as the visible-light-harvesting antenna as well as both electron donor (N-phenylcarbazole, CZ) and acceptor (BDP) on Re bipyridyl framework. Among ReBDP-CZ and ReBDP 2 complexes, the ReBDP 2 incorporating two electrondeficient BDP chromophores had a longer-lived photoexcited state (182.4 μs) and a twofold enhanced molar absorption coefficient (ɛ = 157000 m À 1 cm À 1 ) compared with ReBDP-CZ. Thus, ReBDP 2 achieved the superior photocatalytic reactivity and stability with a CO turnover number (TON CO ) value as high as 1323 and quantum yield (Φ CO ) up to 55 %, which was the most excellent photocatalysis efficiency among the singleactive-site Re catalysts without additional photosensitizer. Furthermore, the acetylene-bridged linker was detrimental to the photoactivity and durability of the catalyst. In brief, two BDP-based Re bipyridyl systems with outstanding catalytic performance and significant visible-light-harvesting capabilities in the solar spectrum offer a promising strategy for solar-to-fuel conversion schemes.
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