Altering the Coordination of Iron Porphyrins by Ionic Liquid Nanodomains in Mixed Solvent Systems

The solvent environment around iron porphyrin complexes was examined using mixed molecular/RTIL (room temperature ionic liquid) solutions. The formation of nanodomains in these solutions provides different solvation environments for substrates that could have significant impact on their chemical reactivity. Iron porphyrins (Fe(P)), whose properties are sensitive to solvent and ligation changes, were used to probe the molecular/RTIL environment. The addition of RTILs to molecular solvents shifted the redox potentials to more positive values. When there was no ligation change upon reduction, the shift in the E° values were correlated to the Gutmann acceptor number, as was observed for other porphyrins with similar charge changes. As %RTIL approached 100 %, there was insufficient THF to maintain coordination and the E° values were much more dependent upon the %RTIL. In the case of FeIII(P)(Cl), the shifts in the E° values were driven by the release of the chloride ion and its strong attraction to the ionic liquid environment. The spectroscopic properties and distribution of the FeII and FeI species into the RTIL nanodomains were monitored with visible spectroelectrochemistry, 19F NMR and EPR spectroscopy. This investigation shows that coordination and charge delocalization (metal versus ligand) in the metalloporphyrins redox products can be altered by the RTIL fraction in the solvent system, allowing an easy tuning of their chemical reactivity

Judicious Ligand Design in Ruthenium Polypyridyl CO2 Reduction Catalysts to Enhance Reactivity by Steric and Electronic Effects

A series of RuII polypyridyl complexes of the structural design [RuII(R−tpy)(NN)(CH3CN)]2+ (R−tpy=2,2′:6′,2′′-terpyridine (R=H) or 4,4′,4′′-tri-tert-butyl-2,2′:6′,2′′-terpyridine (R=tBu); NN=2,2′-bipyridine with methyl substituents in various positions) have been synthesized and analyzed for their ability to function as electrocatalysts for the reduction of CO2 to CO. Detailed electrochemical analyses establish how substitutions at different ring positions of the bipyridine and terpyridine ligands can have profound electronic and, even more importantly, steric effects that determine the complexes’ reactivities. Whereas electron-donating groups para to the heteroatoms exhibit the expected electronic effect, with an increase in turnover frequencies at increased overpotential, the introduction of a methyl group at the ortho position of NN imposes drastic steric effects. Two complexes, [RuII(tpy)(6-mbpy)(CH3CN)]2+ (trans-[3]2+; 6-mbpy=6-methyl-2,2′-bipyridine) and [RuII(tBu−tpy)(6-mbpy)(CH3CN)]2+ (trans-[4]2+), in which the methyl group of the 6-mbpy ligand is trans to the CH3CN ligand, show electrocatalytic CO2 reduction at a previously unreactive oxidation state of the complex. This low overpotential pathway follows an ECE mechanism (electron transfer–chemical reaction–electron transfer), and is a direct result of steric interactions that facilitate CH3CN ligand dissociation, CO2 coordination, and ultimately catalytic turnover at the first reduction potential of the complexes. All experimental observations are rigorously corroborated by DFT calculations

Cyclic voltammetry modeling of proton transport effects on redox charge storage in conductive materials: application to a TiO2 mesoporous film

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Evidencing Fast, Massive, and Reversible H + Insertion in Nanostructured TiO2 Electrodes at Neutral pH. Where Do Protons Come From?

International audienceOngoing developments of sustainable energy technologies based on high-surface-area semiconductive metal oxide electrodes operating under mild and safe aqueous conditions require deep understanding of proton and electron transfer/transport throughout their porous structure. To address this issue, we investigated the electrochemical reductive protonation of high surface area nanostructured amorphous TiO 2 electrodes (produced by glancing angle deposition) in both buffered and unbuffered aqueous solutions. Quantitative analysis of the two charge storage mechanisms was achieved, allowing proper deconvolution of the electrical double-layer capacitive charge storage from the reversible faradaic one resulting from the proton-coupled reduction of bulk TiO 2. We evidence that this latter process occurs reversibly and extensively (up to an intercalation ratio of 20%) not only under strongly acidic pH conditions but also, more interestingly, under neutral pH with the intercalated proton arising from the buffer rather than water. Moreover, we show that in comparison with reductive Li + intercalation the proton-coupled electron charge storage occurs more rapidly (in a few seconds). This important finding suggests that a high-rate and high-power charge storage device could potentially be achieved with the reversible H +-coupled charge/discharge process in TiO 2 at neutral pH, opening thus new opportunities to the development of eco-friendly batteries for electrical energy storage

Cannabis et Grossesse

Le cannabis est une drogue dont la consommation ne cesse d augmenter, chez les jeunes notamment, mais également chez les femmes enceintes. Pour elles, comme pour leur(s) futur(s) enfant(s), cette consommation est à risque et peut avoir des conséquences à court terme, avec l apparition de malformations foetales, mais aussi à long terme avec des problèmes de mémoire, de concentration, d apprentissage et un risque augmenté de développer une psychose schizophrénique. Dans un tel contexte, le pharmacien d officine et les sages femmes ont un rôle de prévention, d écoute et de soutien.ROUEN-BU Médecine-Pharmacie (765402102) / SudocSudocFranceF

Study of pyridine-mediated electrochemical reduction of CO2 to methanol at high CO2 pressure

© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim The recently proposed highly efficient route of pyridine-catalyzed CO 2 reduction to methanol was explored on platinum electrodes at high CO 2 pressure. At 55 bar (5.5 MPa) of CO 2 , the bulk electrolysis in both potentiostatic and galvanostatic regimes resulted in methanol production with Faradaic yields of up to 10 % for the first 5–10 C cm −2 of charge passed. For longer electrolysis, the methanol concentration failed to increase proportionally and was limited to sub-ppm levels irrespective of biasing conditions and pyridine concentration. This limitation cannot be removed by electrode reactivation and/or pre-electrolysis and appears to be an inherent feature of the reduction process. In agreement with bulk electrolysis findings, the CV analysis supported by simulation indicated that hydrogen evolution is still the dominant electrode reaction in pyridine-containing electrolyte solution, even with an excess CO 2 concentration in the solution. No prominent contribution from either a direct or coupled CO 2 reduction was found. The results obtained suggest that the reduction of CO 2 to methanol is a transient process that is largely decoupled from the electrode charge transfer

Efficient and selective molecular catalyst for the CO 2 -to-CO electrochemical conversion in water

Substitution of the four paraphenyl hydrogens of iron tetraphenylporphyrin by trimethylammonio groups provides a watersoluble molecule able to catalyze the electrochemical conversion of carbon dioxide into carbon monoxide. The reaction, performed in pH-neutral water, forms quasi-exclusively carbon monoxide with very little production of hydrogen, despite partial equilibration of CO 2 with carbonic acid-a low pK a acid. This selective molecular catalyst is endowed with a good stability and a high turnover frequency. On this basis, prescribed composition of CO-H 2 mixtures can be obtained by adjusting the pH of the solution, optionally adding an electroinactive buffer. The development of these strategies will be greatly facilitated by the fact that one operates in water. The same applies for the association of the cathode compartment with a proton-producing anode by means of a suitable separator. CO 2 -to-CO conversion | contemporary energy challenges | electrochemistry | catalysis | solar fuels O ne of the most important issues of contemporary energy and environmental challenges consists of reducing carbon dioxide into fuels by means of sunlight (1-3). One route toward this ultimate goal is to first convert solar energy into electricity, which will then be used to reduce CO 2 electrochemically. Direct electrochemical injection of an electron into the CO 2 molecule, forming the corresponding anion radical CO 2 .− requires a very high energy [the standard potential of the CO 2 / CO 2 .− couple is indeed −1.97 V vs. normal hydrogen electrode (NHE) in N,N′dimethylformamide (DMF)] (4, 5). Electrochemical conversion of CO 2 to any reaction product thus requires catalytic schemes that preferably avoid this intermediate. Carbon monoxide may be an interesting step en route to the desired fuels because it can be used as feedstock for the synthesis of alkanes through the classic Fischer-Tropsch process. A number of molecular catalysts for the homogeneous electrochemical CO 2 -to-CO conversion have been proposed. They mainly derive from transition metal complexes by electrochemical generation of an appropriately reduced state, which is restored by the catalytic reaction. So far, nonaqueous aprotic solvents (mostly DMF and acetonitrile) have been used for this purpose (5-16). Brönsted acids have been shown to boost catalysis. However, they should not be too strong, at the risk of leading to H 2 formation at the expense of the CO. Trifluoroethanol and water (possibly in large amounts) have typically played the role of a weak acid in the purpose of boosting catalysis while avoiding hydrogen evolution. One of the most thoroughly investigated families of transitionmetal complex catalysts of CO 2 -to-CO conversion is that of iron porphyrins brought electrochemically to the oxidation degree 0. The importance of coupling electron transfer and introduction of CO 2 into the coordination sphere of iron with proton transfers required by the formation of CO, CO 2 + 2e − , appeared from the very beginning of these studies. Sustained formation of CO was indeed only achieved upon addition of weak and Lewis acids (20, The results thus obtained in nonaqueous or partially aqueous media enabled the discovery of remarkably efficient and selective catalysts of the CO 2 -to-CO conversion. They were also the occasion of notable advances in terms of mechanisms and theory of concerted bond-breaking proton-electron transfer (29). It must, however, be recognized that, from the point of view of practical applications, the use of nonaqueous solvents is not the most exciting aspect of these results. One would rather like to use water as the solvent, which would render more viable the CO 2 -to-CO half-cell reaction as well as its association with a water-oxidation anode through a proton-exchange membrane. Significance CO 2 -to-CO electrochemical conversion is a key step in the production of liquid fuels through dihydrogen-reductive FischerTropsch chemistry. Among molecular catalysts, iron porphyrins reduced electrochemically to the Fe(0) state are particularly efficient and led to a deeper understanding of mechanisms involving coupled bond-breaking proton-electron transfer processes. The replacement of nonaqueous solvents by water should make the CO 2 -to-CO half-cell reaction much more attractive for applications, particularly because it would allow association with a water-oxidation anode through a protonexchange membrane. Here it is demonstrated that electrochemical CO production catalyzed by a water-soluble iron porphyrin can occur with high catalytic efficiency. Manipulation of pH and buffering then allows conversions from those involving complete CO selectivity to ones with prescribed CO-H 2 mixtures

Efficient and selective molecular catalyst for the CO 2 -to-CO electrochemical conversion in water

Substitution of the four paraphenyl hydrogens of iron tetraphenylporphyrin by trimethylammonio groups provides a watersoluble molecule able to catalyze the electrochemical conversion of carbon dioxide into carbon monoxide. The reaction, performed in pH-neutral water, forms quasi-exclusively carbon monoxide with very little production of hydrogen, despite partial equilibration of CO 2 with carbonic acid-a low pK a acid. This selective molecular catalyst is endowed with a good stability and a high turnover frequency. On this basis, prescribed composition of CO-H 2 mixtures can be obtained by adjusting the pH of the solution, optionally adding an electroinactive buffer. The development of these strategies will be greatly facilitated by the fact that one operates in water. The same applies for the association of the cathode compartment with a proton-producing anode by means of a suitable separator. CO 2 -to-CO conversion | contemporary energy challenges | electrochemistry | catalysis | solar fuels O ne of the most important issues of contemporary energy and environmental challenges consists of reducing carbon dioxide into fuels by means of sunlight (1-3). One route toward this ultimate goal is to first convert solar energy into electricity, which will then be used to reduce CO 2 electrochemically. Direct electrochemical injection of an electron into the CO 2 molecule, forming the corresponding anion radical CO 2 .− requires a very high energy [the standard potential of the CO 2 / CO 2 .− couple is indeed −1.97 V vs. normal hydrogen electrode (NHE) in N,N′dimethylformamide (DMF)] (4, 5). Electrochemical conversion of CO 2 to any reaction product thus requires catalytic schemes that preferably avoid this intermediate. Carbon monoxide may be an interesting step en route to the desired fuels because it can be used as feedstock for the synthesis of alkanes through the classic Fischer-Tropsch process. A number of molecular catalysts for the homogeneous electrochemical CO 2 -to-CO conversion have been proposed. They mainly derive from transition metal complexes by electrochemical generation of an appropriately reduced state, which is restored by the catalytic reaction. So far, nonaqueous aprotic solvents (mostly DMF and acetonitrile) have been used for this purpose (5-16). Brönsted acids have been shown to boost catalysis. However, they should not be too strong, at the risk of leading to H 2 formation at the expense of the CO. Trifluoroethanol and water (possibly in large amounts) have typically played the role of a weak acid in the purpose of boosting catalysis while avoiding hydrogen evolution. One of the most thoroughly investigated families of transitionmetal complex catalysts of CO 2 -to-CO conversion is that of iron porphyrins brought electrochemically to the oxidation degree 0. The importance of coupling electron transfer and introduction of CO 2 into the coordination sphere of iron with proton transfers required by the formation of CO, CO 2 + 2e − , appeared from the very beginning of these studies. Sustained formation of CO was indeed only achieved upon addition of weak and Lewis acids (20, The results thus obtained in nonaqueous or partially aqueous media enabled the discovery of remarkably efficient and selective catalysts of the CO 2 -to-CO conversion. They were also the occasion of notable advances in terms of mechanisms and theory of concerted bond-breaking proton-electron transfer (29). It must, however, be recognized that, from the point of view of practical applications, the use of nonaqueous solvents is not the most exciting aspect of these results. One would rather like to use water as the solvent, which would render more viable the CO 2 -to-CO half-cell reaction as well as its association with a water-oxidation anode through a proton-exchange membrane. Significance CO 2 -to-CO electrochemical conversion is a key step in the production of liquid fuels through dihydrogen-reductive FischerTropsch chemistry. Among molecular catalysts, iron porphyrins reduced electrochemically to the Fe(0) state are particularly efficient and led to a deeper understanding of mechanisms involving coupled bond-breaking proton-electron transfer processes. The replacement of nonaqueous solvents by water should make the CO 2 -to-CO half-cell reaction much more attractive for applications, particularly because it would allow association with a water-oxidation anode through a protonexchange membrane. Here it is demonstrated that electrochemical CO production catalyzed by a water-soluble iron porphyrin can occur with high catalytic efficiency. Manipulation of pH and buffering then allows conversions from those involving complete CO selectivity to ones with prescribed CO-H 2 mixtures

Insights into the influence of the Ag loading on Al2O3 in the H2-assisted C3H6-SCR of NOx

International audienceThe addition of H2 has been reported to promote drastically the selective catalytic reduction of NOx by hydrocarbons (HC-SCR). Yet, the influence of the Ag loading on the H2-promoted HC-SCR has been the subject of a very limited number of investigations. The H2-HC-SCR earlier studies reported mostly on Ag/Al2O3 samples containing about 2 wt% Ag, since this particular loading has been shown to provide optimum catalytic performances in the HC-SCR reaction in the absence of H2. The present study highlights for the first time that the H2-C3H6-SCR catalytic performances of Ag/Al2O3 samples improved in the 150–550 °C temperature domain as the Ag loading (Ag surface density: x (View the MathML sourceAg/nmAl2O32)) decreased well below 2 wt%. A detailed kinetic study of H2-C3H6-SCR was performed in which the reaction orders in NO, C3H6 and H2, and the apparent activation energies were determined for the reduction of NOx to N2 on a Ag(x)/Al2O3 catalysts series, for which Ag was found to be in a highly dispersed state by TEM and HAADF-STEM. Remarkably, changes in these kinetic parameters were found to occur at an Ag surface density close to View the MathML source0.7 Ag/nmAl2O32 (Ag loading of 2.2 wt%) coinciding with the changes observed earlier in the NOx uptakes of the Al2O3 supporting oxide [18]. Interpretation of the activity and kinetic data led us to conclude that the H2-C3H6-SCR reaction proceeds via the activation of H2 and C3H6 on Ag species and their further reaction with NOx adspecies activated on the Al2O3 support. The unexpected higher catalytic performances of the Ag samples with the lower Ag surface densities was attributed to the higher concentration of active sites on the Al2O3 supporting oxide able to chemisorb NOx species, in agreement with the NOx uptake data. The kinetic data obtained for Ag surface densities lower than View the MathML source0.7 Ag/nmAl2O32 also suggest that the interaction between NOx and C3H6 adspecies would be rate determining in the C3H6-SCR process