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1.
Chem Soc Rev ; 49(20): 7271-7283, 2020 Oct 19.
Artigo em Inglês | MEDLINE | ID: mdl-32954394

RESUMO

Artificial photosynthesis is considered as one of the most promising strategies for solar-to-fuel conversion through sunlight-driven water splitting and CO2 reduction. This tutorial describes recent developments in the use of metal quaterpyridine complexes as electrocatalyts and photocatalysts for artificial photosynthesis.

2.
Inorg Chem ; 59(16): 11577-11583, 2020 Aug 17.
Artigo em Inglês | MEDLINE | ID: mdl-32799464

RESUMO

O2 activation under mild conditions remains a weighty challenge for chemists. Herein we report a study of electrochemical O2 reductive activation catalyzed by FeIII(F20TPP)Cl, by means of cyclic voltammetry and UV-vis spectroelectrochemistry in acidic solutions of N,N-dimethylformamide. Two parallel catalytic pathways have been evidenced occurring at different overpotentials. At high overpotential a classical electron-proton (EPT) pathway where protonation of Fe peroxo ultimately leads to the formation of high-valent Fe oxo species dominates. At low overpotential a proton-electron (PET) pathway involving a hydrosuperoxo species has been identified.

3.
Dalton Trans ; 49(46): 16623-16626, 2020 Dec 08.
Artigo em Inglês | MEDLINE | ID: mdl-32725016

RESUMO

In this work we provide direct experimental evidence on the correlation of remote interactions between a newly synthesized MnI-complex (1) and different alkali cations with redox potential tuning. Furthermore we report the electrochemical behavior of 1 towards carbon dioxide, including the effects of added alkali salts using cyclic voltammetry.

4.
ChemSusChem ; 13(16): 4111-4120, 2020 Aug 21.
Artigo em Inglês | MEDLINE | ID: mdl-32657523

RESUMO

Iron complexes with a N2 O2 -type N,N'-bis(salicylaldehyde)-1,2-phenylenediamine salophen ligand catalyze the electrochemical reduction of CO2 to CO in acetonitrile with phenol as the proton donor, giving rise to 90-99 % selectivity, faradaic efficiency up to 58 %, and turnover frequency up to 103  s-1 at an overpotential of 0.65 V. This novel class of molecular catalyst for CO2 reduction operate through a mononuclear FeI intermediate, with phenol being involved in the process with first-order kinetics. The molecular nature of the catalyst and the low cost, easy synthesis and functionalization of the salophen ligand paves the way for catalyst engineering and optimization. Competitive electrodeposition of the coordination complex at the electrode surface results in the formation of iron-based nanoparticles, which are active towards heterogeneous electrocatalytic processes mainly leading to proton reduction to hydrogen (faradaic efficiency up to 80 %) but also to the direct reduction of CO2 to methane with a faradaic efficiency of 1-2 %.

5.
Nat Commun ; 11(1): 3499, 2020 Jul 13.
Artigo em Inglês | MEDLINE | ID: mdl-32661340

RESUMO

Artificial photosynthesis is a vibrant field of research aiming at converting abundant, low energy molecules such as water, nitrogen or carbon dioxide into fuels or useful chemicals by means of solar energy input. Photo-electrochemical reduction of carbon dioxide is an appealing strategy, aiming at reducing the greenhouse gas into valuable products such as carbon monoxide at low or without bias voltage. Yet, in such configuration, there is no catalytic system able to produce carbon monoxide selectively in aqueous media with high activity, and using earth-abundant molecular catalyst. Upon associating a p-type Cu(In,Ga)Se2 semi-conductor with cobalt quaterpyridine complex, we herein report a photocathode complying with the aforementioned requirements. Pure carbon dioxide dissolved in aqueous solution (pH 6.8) is converted to carbon monoxide under visible light illumination with partial current density above 3 mA cm-2 and 97% selectivity, showing good stability over time.

6.
ChemSusChem ; 13(23): 6360-6369, 2020 Dec 07.
Artigo em Inglês | MEDLINE | ID: mdl-32672415

RESUMO

A straightforward procedure has been developed to prepare a porous carbon material decorated with iron by direct pyrolysis of a mixture of a porous polymer and iron chloride. Characterization of the material with X-ray diffraction, X-ray absorption spectroscopy, and electron microscopy indicates the presence of iron carbide nanoparticles encapsulated inside the carbon matrix, and elemental mapping and cyanide poisoning experiments demonstrate the presence of atomic Fe centers, albeit in trace amounts, which are active sites for electrochemical CO2 reduction. The encapsulated iron carbide nanoparticles are found to boost the catalytic activity of atomic Fe sites in the outer carbon layers, rendering the material highly active and selective for CO2 reduction, although these atomic Fe sites are only present in trace amounts. The target material exhibits near-unity selectivity (98 %) for CO2 -to-CO conversion at a small overpotential (410 mV) in water. Furthermore, the material holds potential for practical application, as a current density over 30 mA cm-2 and a selectivity of 93 % can be achieved in a flow cell.

7.
Chem Commun (Camb) ; 56(54): 7491-7494, 2020 Jul 11.
Artigo em Inglês | MEDLINE | ID: mdl-32497158

RESUMO

The photocatalytic generation of an NADH synthetic analogue, i.e. 1-benzyl-1,4-dihydronicotinamide (1,4-BNAH), has been studied using the cobalt diimino-dioxime complexes and the BF2-bridged derivative as catalysts. 1,4-BNAH was produced in both aqueous and organic media at unprecedented turnover numbers with metal and organic photosensitizers, respectively.

8.
Chem Commun (Camb) ; 56(46): 6249-6252, 2020 Jun 11.
Artigo em Inglês | MEDLINE | ID: mdl-32373815

RESUMO

The iron(ii) complex bearing the 2,2':6',2'':6'',2''':6''',2''''-quinquepyridine (qnpy) ligand, [Fe(qnpy)(H2O)2]2+, is a highly efficient and robust catalyst for photocatalytic reduction of CO2 to CO in aqueous acetonitrile solution. A turnover number (TON) for CO of up to 14 095 with 98% selectivity can be achieved using Ru(phen)3Cl2 (phen = 1,10-phenanthroline) as the photosensitizer and BIH (1,3-dimethyl-2-phenyl-2,3-dihydro-1H-benzo[d]imidazole) as the sacrificial reductant in a CO2-saturated MeCN/H2O (1 : 1, v/v) solution under visible light irradiation. This Fe complex is state-of-the-art for CO2 visible-light-driven catalysis.

10.
J Am Chem Soc ; 142(13): 6188-6195, 2020 Apr 01.
Artigo em Inglês | MEDLINE | ID: mdl-32148034

RESUMO

Achieving visible-light-driven carbon dioxide reduction with high selectivity control and durability while using only earth abundant elements requires new strategies. Hybrid catalytic material was prepared upon covalent grafting a Co-quaterpyridine molecular complex to semiconductive mesoporous graphitic carbon nitride (mpg-C3N4) through an amide linkage. The molecular material was characterized by various spectroscopic techniques, including XPS, IR, and impedance spectroscopy. It proved to be a selective catalyst for CO production in acetonitrile using a solar simulator with a high 98% selectivity, while being remarkably robust since no degradation was observed after 4 days of irradiation (ca. 500 catalytic cycles). This unique combination of a selective molecular catalyst with a simple and robust semiconductive material opens new pathways for CO2 catalytic light-driven reduction.

11.
Dalton Trans ; 49(14): 4257-4265, 2020 Apr 07.
Artigo em Inglês | MEDLINE | ID: mdl-32129388

RESUMO

CO2 reduction research is at a critical turnaround since it has the potential to partially or even substantially fulfil future clean energy needs. CO2-to-CO electrochemical conversion is getting closer from industrial implementation requirements. Efforts are now more and more directed to obtain highly reduced products such as methanol, methane, ethylene, ethanol, etc., most of them being liquids. Gas-phase products (e.g., CO, CH4) are typically detected and quantified by well-defined gas chromatography (GC and GC/MS) protocols. On the other hand, NMR, GC-MS, HPLC have been used for the liquid phase characterization, but no routine technique has yet been established, mainly due to lack of versatility of a single technique. Additionally, except NMR and GC-MS, classical techniques cannot distinguish 13C from 12C products, although it is a mandatory step to assess products origin. Herein, we show the efficiency and applicability of 1H NMR as routine technique for liquid phase products analysis and we address two previous shortcomings. We first established a comprehensive 1H and 13C NMR chemical shifts list for all 12CO2 and 13CO2 reduction products in water ranging from C1 to C3. Then we overcame the difficulty of identifying aqueous formaldehyde intermediate by 1H NMR through an efficient chemical trapping step, along with isotopic signature study. Formaldehyde can be reliably quantified in water with a concentration as low as 50 µM.

12.
Chemistry ; 26(14): 3034-3038, 2020 Mar 09.
Artigo em Inglês | MEDLINE | ID: mdl-31943389

RESUMO

Molecular catalysts have been shown to have high selectivity for CO2 electrochemical reduction to CO, but with current densities significantly below those obtained with solid-state materials. By depositing a simple Fe porphyrin mixed with carbon black onto a carbon paper support, it was possible to obtain a catalytic material that could be used in a flow cell for fast and selective conversion of CO2 to CO. At neutral pH (7.3) a current density as high as 83.7 mA cm-2 was obtained with a CO selectivity close to 98 %. In basic solution (pH 14), a current density of 27 mA cm-2 was maintained for 24 h with 99.7 % selectivity for CO at only 50 mV overpotential, leading to a record energy efficiency of 71 %. In addition, a current density for CO production as high as 152 mA cm-2 (>98 % selectivity) was obtained at a low overpotential of 470 mV, outperforming state-of-the-art noble metal based catalysts.

13.
Angew Chem Int Ed Engl ; 58(45): 16172-16176, 2019 Nov 04.
Artigo em Inglês | MEDLINE | ID: mdl-31496012

RESUMO

Conversion of CO2 into valuable molecules is a field of intensive investigation with the aim of developing scalable technologies for making fuels using renewable energy sources. While electrochemical reduction into CO and formate are approaching industrial maturity, a current challenge is obtaining more reduced products like methanol. However, literature on the matter is scarce, and even more for the use of molecular catalysts. Here, we demonstrate that cobalt phthalocyanine, a well-known catalyst for the electrochemical conversion of CO2 to CO, can also catalyze the reaction from CO2 or CO to methanol in aqueous electrolytes at ambient conditions of temperature and pressure. The studies identify formaldehyde as a key intermediate and an unexpected pH effect on selectivity. This paves the way for establishing a sequential process where CO2 is first converted to CO which is subsequently used as a reactant to produce methanol. Under ideal conditions, the reaction shows a global Faradaic efficiency of 19.5 % and chemical selectivity of 7.5 %.

14.
Nat Commun ; 10(1): 3602, 2019 Aug 09.
Artigo em Inglês | MEDLINE | ID: mdl-31399585

RESUMO

Molecular catalysts that combine high product selectivity and high current density for CO2 electrochemical reduction to CO or other chemical feedstocks are urgently needed. While earth-abundant metal-based molecular electrocatalysts with high selectivity for CO2 to CO conversion are known, they are characterized by current densities that are significantly lower than those obtained with solid-state metal materials. Here, we report that a cobalt phthalocyanine bearing a trimethyl ammonium group appended to the phthalocyanine macrocycle is capable of reducing CO2 to CO in water with high activity over a broad pH range from 4 to 14. In a flow cell configuration operating in basic conditions, CO production occurs with excellent selectivity (ca. 95%), and good stability with a maximum partial current density of 165 mA cm-2 (at -0.92 V vs. RHE), matching the most active noble metal-based nanocatalysts. These results represent state-of-the-art performance for electrolytic carbon dioxide reduction by a molecular catalyst.

15.
ChemSusChem ; 12(19): 4500-4505, 2019 Oct 08.
Artigo em Inglês | MEDLINE | ID: mdl-31432616

RESUMO

A Fe quaterpyridine complex was used as a molecular precursor for the electrochemical reduction of CO2 to CH4 in acetonitrile in the presence of triethanolamine. CH4 was produced with a faradaic yield of approximately 2.1 % at 25 °C and 1 atm pressure of CO2 as reactant. Controlled potential electrolysis coupled to ex situ X-ray photoelectron spectroscopy and X-ray absorption spectroscopy of the electrode surface revealed the formation of metallic iron covered by iron oxides as species responsible for catalysis.

16.
Science ; 365(6451): 367-369, 2019 07 26.
Artigo em Inglês | MEDLINE | ID: mdl-31346062

RESUMO

Practical electrochemical carbon dioxide (CO2) conversion requires a catalyst capable of mediating the efficient formation of a single product with high selectivity at high current densities. Solid-state electrocatalysts achieve the CO2 reduction reaction (CO2RR) at current densities ≥ 150 milliamperes per square centimeter (mA/cm2), but maintaining high selectivities at high current densities and efficiencies remains a challenge. Molecular CO2RR catalysts can be designed to achieve high selectivities and low overpotentials but only at current densities irrelevant to commercial operation. We show here that cobalt phthalocyanine, a widely available molecular catalyst, can mediate CO2 to CO formation in a zero-gap membrane flow reactor with selectivities > 95% at 150 mA/cm2 The revelation that molecular catalysts can work efficiently under these operating conditions illuminates a distinct approach for optimizing CO2RR catalysts and electrolyzers.

17.
MAGMA ; 32(6): 669-677, 2019 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-31338627

RESUMO

OBJECTIVE: Purely exponential decay is rarely observed in conventional mono-exponential T2 mapping due to transmit field inhomogeneity and calibration errors, which collectively introduce stimulated and indirect echo pathways. Stimulated echo correction (SEC) requires an additional fit parameter for the transmit field, resulting in greater uncertainty in T2 relative to mono-exponential fitting. The aim of this study was to develop an accurate and precise method for T2 mapping using SEC. METHODS: The proposed method, called two-step SEC (tSEC), leverages spatial correlations in the transmit field to reduce the number of fully independent fitting parameters from three to two. The method involves a two-pass fit: the first pass involves a fast but standard SEC fit. The initially estimated transmit field is smoothed and provided as a fixed input to the second pass. RESULTS: Simulations and in vivo experiments demonstrated up to 38% and 27% decreases in relative T2 variance with tSEC relative to SEC. Average T2 values were unchanged between tSEC and SEC fits. The proposed method uses the same input data as SEC and exponential fits, so it is applicable to existing data. DISCUSSION: The proposed method generates reliable and reproducible quantitative T2 maps and should be considered for future relaxometry studies.


Assuntos
Mapeamento Encefálico/métodos , Encéfalo/diagnóstico por imagem , Aumento da Imagem/métodos , Interpretação de Imagem Assistida por Computador/métodos , Imagem por Ressonância Magnética , Adulto , Algoritmos , Simulação por Computador , Feminino , Voluntários Saudáveis , Humanos , Masculino , Modelos Teóricos , Imagens de Fantasmas , Reprodutibilidade dos Testes
18.
Hum Brain Mapp ; 40(15): 4345-4356, 2019 10 15.
Artigo em Inglês | MEDLINE | ID: mdl-31282058

RESUMO

White matter development has been well described using diffusion tensor imaging (DTI), but the microstructural processes driving development remain unclear due to methodological limitations. Here, using neurite orientation dispersion and density imaging (NODDI), inhomogeneous magnetization transfer (ihMT), and multicomponent driven equilibrium single-pulse observation of T1/T2 (mcDESPOT), we describe white matter development at the microstructural level in a longitudinal cohort of healthy 6-15 year olds. We evaluated age and gender-related trends in fractional anisotropy (FA), mean diffusivity (MD), neurite density index (NDI), orientation dispersion index (ODI), quantitative ihMT (qihMT), myelin volume fraction (VFm ), and g-ratio. We found age-related increases of VFm in most regions, showing ongoing myelination in vivo during late childhood and adolescence for the first time. No relationship was observed between qihMT and age, suggesting myelin volume increases are driven by increased water content. Age-related increases were observed for NDI, suggesting axonal packing is also occurring during this time. g-ratio decreased with age in the uncinate fasciculus, implying changes in communication efficiency are ongoing in this region. FA increased and MD decreased with age in most regions. Gender effects were present in the left cingulum for FA, and an age-by-gender interaction was found for MD in the left uncinate fasciculus. These findings suggest that FA and MD remain useful markers of gender-related processes, and gender differences are likely driven by factors other than myelin. We conclude that white matter development during late childhood and adolescence is driven by a combination of axonal packing and myelin volume increases.


Assuntos
Imagem de Difusão por Ressonância Magnética/métodos , Neuritos/ultraestrutura , Substância Branca/crescimento & desenvolvimento , Adolescente , Fatores Etários , Anisotropia , Água Corporal , Criança , Imagem de Difusão por Ressonância Magnética/estatística & dados numéricos , Feminino , Seguimentos , Humanos , Modelos Lineares , Masculino , Bainha de Mielina/fisiologia , Tamanho do Órgão , Valores de Referência , Caracteres Sexuais , Fatores Sexuais , Substância Branca/diagnóstico por imagem , Substância Branca/ultraestrutura
19.
Dalton Trans ; 48(18): 5869-5878, 2019 May 07.
Artigo em Inglês | MEDLINE | ID: mdl-30848271

RESUMO

Substituted tetraphenyl Fe porphyrins are versatile molecular catalysts for the activation of small molecules (such as O2, H+ or CO2), which could lead to renewable energy storage, the direct production of fuels or new catalytic relevant processes. Herein, we review the recent studies of these earth-abundant metal catalysts for the electrochemical activation of dioxygen on the one hand and for the photostimulated reduction of carbon dioxide on the other hand. These two prototype reactions illustrate how mechanistic studies are the only rational approach to gain fundamental insights into the elementary steps that drive the catalysis and for identification of the key intrinsic parameters controlling the reactivity, offering in turn the possibility to rationally tune the structure of the catalysts as well as the catalytic conditions.

20.
Dalton Trans ; 48(26): 9596-9602, 2019 Jul 02.
Artigo em Inglês | MEDLINE | ID: mdl-30778461

RESUMO

A new pentadentate quinoline-pyridine ligand and its iron (1), cobalt (2) and nickel (3) complexes have been synthesized and characterized. The iron complex exhibits excellent photocatalytic activity towards CO2-to-CO conversion with a TON(CO) of 544 and a selectivity of 99.3% using the commercially available organic dye purpurin as the photosensitiser and BIH as the electron donor. In contrast, the cobalt and nickel complexes result in very low activity for CO production with a TON of only 8 and 15, respectively. On the other hand, all the three complexes show good electrocatalytic activity for CO2 reduction when using 2,2,2-trifluoroethanol as the proton source with the active intermediate of M0 species. The lack of activity in photocatalytic CO2 reduction by 2 and 3 can be attributed to the redox potential of MI/M0 which is significantly more negative than that of PP-/PP2- while in the case of 1 the FeI/Fe0 redox potential becomes more positive than that of the PP-/PP2- couple.

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