The photochemical reduction of CO2 to chemical resources has displayed the promise to solve energy and environmental problems. To facilitate this reaction, a considerable challenge is to design not ...only highly efficient and selective, but also economic catalysts. In this study, we report a homogeneous catalyst, CoL1(CH3CN)(ClO4)2 (1, L1=Tris2‐(iso‐propylamino)ethylamine) which displays high activity and selectivity for CO2 reduction to CO driven by visible light in a water‐containing system, with turnover numbers (TONCO) and turnover frequencies (TOF), and CO selectivity values of 44800, 1.24 s−1 and 97 %, respectively. The excellent performances of 1 for the photocatalytic CO2‐to‐CO conversion is confirmed by control experiments and its catalytic mechanism is corroborated by DFT calculations.
The mononuclear option: A mononuclear cobalt complex supported by a tripodal ligand, exhibits high activity and selectivity for the photocatalytic reduction of CO2 to CO in a water‐containing system. The TON and TOF values are higher than most reported molecular catalysts for photocatalytic CO2 reduction. Control experiments and DFT calculations results demonstrate that 1 is an excellent candidate for photocatalytic conversion of CO2 to CO.
•Non-noble metal based molecular complexes for CO2 reduction have been reviewed from the ligand design perspective.•The relationship between catalytic performance and ligand structure has been ...discussed and concluded.•Constructive suggestions in designing efficient molecular catalysts for CO2 reduction have been put forward.
Molecular catalysts for electrochemical and photochemical CO2 reduction have developed rapidly during the past two decades. Using non-noble metal (Ni, Co, Mn, Fe, and Cu) complexes as molecular catalyst, numerous catalytic systems have shown good catalytic performance for CO2 reduction. It is useful to draw conclusions from the results of reported works and identify concepts that may provide future frameworks in catalyst design for CO2 reduction. It is well-known that the ligand in molecular complexes is one of the key factors affecting catalytic performance. Modification of the ligand structure has become an important strategy to improve the catalytic performance. This review, beginning with a brief general introduction to molecular catalysis of CO2 reduction, intends to reveal ligand effects of non-noble metal complexes on the catalytic performance for CO2 reduction. The latest progress on both electrocatalytic and photocatalytic CO2 reduction by non-noble metal complexes has been summarized, wherein, emphasis has been placed on the effect of ligands on catalyst efficiency, selectivity and stability. New developments involving immobilization of non-noble metal complexes on solid supports or electrodes have also been discussed. Finally, several constructive suggestions in designing efficient molecular catalysts for CO2 reduction have been put forward.
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The reaction kinetics of photocatalytic CO
reduction is highly dependent on the transfer rate of electrons and protons to the CO
molecules adsorbed on catalytic centers. Studies on uncovering the ...proton effect in catalysts on photocatalytic activity of CO
reduction are significant but rarely reported. In this paper, we, from the molecular level, revealed that the photocatalytic activity of CO
reduction is closely related to the proton availability in catalysts. Specifically, four dinuclear Co(II) complexes based on Robson-type ligands with different number of carboxylic groups (-
COOH;
= 0, 2, 4, 6) were designed and synthesized. All these complexes show photocatalytic activity for CO
reduction to CO in a water-containing system upon visible-light illumination. Interestingly, the CO yields increase positively with the increase of the carboxylic-group number in dinuclear Co(II) complexes. The one containing -6COOH shows the best photocatalytic activity for CO
reduction to CO, with the TON value reaching as high as 10,294. The value is 1.8, 3.4, and 7.8 times higher than those containing -4COOH, -2COOH, and -0COOH, respectively. The high TON value also makes the dinuclear Co(II) complex with -6COOH outstanding among reported homogeneous molecular catalysts for photocatalytic CO
reduction. Control experiments and density functional theory calculation indicated that more carboxylic groups in the catalyst endow the catalyst with more proton relays, thus accelerating the proton transfer and boosting the photocatalytic CO
reduction. This study, at a molecular level, elucidates that more carboxylic groups in catalysts are beneficial for boosting the reaction kinetics of photocatalytic CO
reduction.
The reaction kinetics of photocatalytic CO2 reduction is highly dependent on the transfer rate of electrons and protons to the CO2 molecules adsorbed on catalytic centers. Studies on uncovering the ...proton effect in catalysts on photocatalytic activity of CO2 reduction are significant but rarely reported. In this paper, we, from the molecular level, revealed that the photocatalytic activity of CO2 reduction is closely related to the proton availability in catalysts. Specifically, four dinuclear Co(II) complexes based on Robson-type ligands with different number of carboxylic groups (–nCOOH; n = 0, 2, 4, 6) were designed and synthesized. All these complexes show photocatalytic activity for CO2 reduction to CO in a water-containing system upon visible-light illumination. Interestingly, the CO yields increase positively with the increase of the carboxylic-group number in dinuclear Co(II) complexes. The one containing –6COOH shows the best photocatalytic activity for CO2 reduction to CO, with the TON value reaching as high as 10,294. The value is 1.8, 3.4, and 7.8 times higher than those containing –4COOH, –2COOH, and –0COOH, respectively. The high TON value also makes the dinuclear Co(II) complex with –6COOH outstanding among reported homogeneous molecular catalysts for photocatalytic CO2 reduction. Control experiments and density functional theory calculation indicated that more carboxylic groups in the catalyst endow the catalyst with more proton relays, thus accelerating the proton transfer and boosting the photocatalytic CO2 reduction. This study, at a molecular level, elucidates that more carboxylic groups in catalysts are beneficial for boosting the reaction kinetics of photocatalytic CO2 reduction.
There is a demand to develop molecular catalysts promoting the hydrogen evolution reaction (HER) with a high catalytic rate and a high tolerance to various inhibitors, such as CO and O
. Herein we ...report a cobalt catalyst with a penta-dentate macrocyclic ligand (1-Co), which exhibits a fast catalytic rate (TOF=2210 s
) in aqueous pH 7.0 phosphate buffer solution, in which proton transfer from a dihydrogen phosphate anion (H
PO
) plays a key role in catalytic enhancement. The electrocatalyst exhibits a high tolerance to inhibitors, displaying over 90 % retention of its activity under either CO or air atmosphere. Its high tolerance to CO is concluded to arise from the kinetically labile character of undesirable CO-bound species due to the geometrical frustration posed by the ligand, which prevents an ideal trigonal bipyramid being established.
A template co-pyrolysis strategy was developed to prepare C–NHx-rich (x = 1 or 2) g-C3N4, which can greatly increase the CO2 binding and the subsequent photocatalytic CO2 reduction efficiency, over ...74-fold higher than that of g-C3N4 conventionally prepared.
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•A template co-pyrolysis strategy was developed to prepare C–NHx-rich g-C3N4.•The resulted C–NHx-rich g-C3N4 shows greatly increased CO2 binding.•The C–NHx-rich g-C3N4 shows excellent photocatalytic CO2 reduction efficiency.
Photocatalytic CO2 reduction reaction (CO2RR) is an effective mean to address the current environmental and energy issues. As a kind of typical photocatalyst, g-C3N4 possesses lots of advantages (i.e., facile synthesis, visible-light response, and high stability) in CO2 reduction. However, the poor capacity of CO2 capture and rapid recombination of photo-generated electron and hole, both hinder the further development of g-C3N4 for CO2RR. Herein, we developed a template co-pyrolysis strategy to prepare C–NHx-rich (x = 1 or 2) g-C3N4, to increase the CO2 binding and the subsequent photocatalytic CO2 reduction efficiency. Specifically, organic molecules with multiple imino groups were used as additives to co-pyrolyze with urea. These additives can act as templates to facilitate the formation of g-C3N4 with abundant C–NHx groups, which effectively improved the capacity of CO2 capture. Meanwhile, the capacity of light absorption and the separation of photo-generated electron and hole were also optimized. As a result, the obtained C–NHx-rich g-C3N4 showed greatly enhanced photocatalytic activity for CO2RR, over 74-fold higher than that of g-C3N4 conventionally prepared. This work provides a new avenue for optimizing the g-C3N4-based photocatalysts for CO2RR.
A carbazolide-bis(NHC) NiII catalyst (1; NHC, N-heterocyclic carbene) for selective CO2 photoreduction was designed herein by a one-stone-two-birds strategy. The extended π-conjugation and the strong ...σ/π electron-donation characteristics (two birds) of the carbazolide fragment (one stone) lead to significantly enhanced activity for photoreduction of CO2 to CO. The turnover number (TON) and turnover frequency (TOF) of 1 were ninefold and eightfold higher than those of the reported pyridinol-bis(NHC) NiII complex at the same catalyst concentration using an identical Ir photosensitizer, respectively, with a selectivity of ∼100%. More importantly, an organic dye was applied to displace the Ir photosensitizer to develop a noble-metal-free photocatalytic system, which maintained excellent performance and obtained an outstanding quantum yield of 11.2%. Detailed investigations combining experimental and computational studies revealed the catalytic mechanism, which highlights the potential of the one-stone-two-birds effect.
Covalent organic frameworks (COFs) have been widely studied in photocatalytic CO
reduction reaction (CO
RR). However, pristine COFs usually exhibit low catalytic efficiency owing to the fast ...recombination of photogenerated electrons and holes. In this study, we fabricated a stable COF-based composite (GO-COF-366-Co) by covalently anchoring COF-366-Co on the surface of graphene oxide (GO) for the photocatalytic CO
reduction. Interestingly, in absolute acetonitrile (CH
CN), GO-COF-366-Co shows a high selectivity of 94.4 % for the photoreduction of CO
to formate, with a formate yield of 15.8 mmol/g, which is approximately four times higher than that using the pristine COF-366-Co. By contrast, in CH
CN/H
O (v : v=4 : 1), the main product for the photocatalytic CO
reduction over GO-COF-366-Co is CO (96.1 %), with a CO yield as high as 52.2 mmol/g, which is also approximately four times higher than that using the pristine COF-366-Co. Photoelectrochemical experiments demonstrate the covalent bonding of COF-366-Co and GO to form the GO-COF-366-Co composite facilitates charge separation and transfer significantly, thereby accounting for the enhanced catalytic activity. In addition, theoretical calculations and in situ Fourier transform infrared spectroscopy reveal H
O can stabilize the *COOH intermediate to further form a *CO intermediate via O-H(aq)⋅⋅⋅O(*COOH) hydrogen bonding, thus explaining the regulated photocatalytic performance.
Chemical hydrogen storage, endowed with superiorities of safety and efficiency, has been regarded as one of the most promising approaches. The design and synthesis of metallic catalytic system is an ...key step for development of chemical hydrogen storate materials. In this paper, we report that RhNi nanocatalyst, formed by spontaneously alloying of well-dispersed Rh and Ni NPs, exhibits much higher performance in the catalytic dehydrogenation of hydrous hydrazine.
RhNi nanocatalyst, formed by spontaneously alloying of well-dispersed Rh and Ni NPs, exhibits much higher performance in the catalytic dehydrogenation of hydrous hydrazine. Display omitted
•Monometallic Rh and Ni nanoparticles can spontaneously alloy into bimetallic RhNi nanoparticles.•RhNi alloy nanoparticles have been characterized by XRD, SAED, HAADF-STEM, and EDS.•RhNi alloy nanocatalysts exhibit much higher performance in the catalytic dehydrogenation of hydrous hydrazine.
