Faraday Discussions最新文献

Electrochemical and catalytic conversion to and from ammonia is strongly enhanced by appropriate choice of hydrogen conducting electrolyte or substrate. Here we explore both protonic and hydride ionic conductors in relation to ammonia conversions. Protonic conductors tend to require too high a temperature to achieve sufficient hydrogen flux for ammonia synthesis as thermal decomposition competes strongly. Conversely protonic conductors are well suited to direct ammonia fuel cell use. Hydride ions can be very mobile and are strongly reducing. Alkaline hydride lattices can exhibit facile H and N mobility and exchange and offer a very promising basis for ammonia conversion and synthesis.

There is a need to develop rapidly responsive chemical sensors for the detection of low concentrations of volatile organic solvents (VOCs). Platinum pincer complexes have shown promise as sensors because of their colours and vapochromic and solvatochromic properties, that may be related to the non-covalent interactions between the pincer complexes and the guest VOCs. Here we report an investigation into a series of Pt(II) complexes based on the 1,3-di(pyridine)benzene tridentate (N⁁C⁁N) skeleton with the formula [Pt(N⁁C(R)⁁N)(CN)] (R = C(O)Me 2, C(O)OEt 3, C(O)OPh 4) with the fourth coordination site occupied by a cyanide ligand. Solid-state samples of the complexes have been tested with a range of volatiles including methanol, ethanol, acetone, dichloromethane and water, and while 2 displays thermochromism, 3 and 4 display rapidly reversible vapochromism and solvatochromism. These results are correlated with X-ray powder and single crystal X-ray structural data including an assessment of the crystal packing and the void space in the crystalline space. The cyanide ligand and the R substituents are involved in hydrogen bonding that creates the voids within the structures and interact with the solvent molecules that influence the Pt⋯Pt separation in the crystalline state.

Nitrogenases catalyse the 6-electron reduction of dinitrogen to ammonia, passing through a series of redox and protonation levels during catalytic substrate reduction. The molybdenum–iron nitrogenase is the most well-studied, but redox potentials associated with proton-coupled transformations between the redox levels of the catalytic MoFe protein have proved difficult to pin down, in part due to a complex electron-transfer pathway from the partner Fe protein, linked to ATP-hydrolysis. Here, we apply electrochemical control to the MoFe protein of Azotobacter vinelandii nitrogenase, using europium(III/II)-ligand couples as low potential redox mediators. We combine insight from the electrochemical current response with data from gas chromatography and in situ infrared spectroscopy, in order to define potentials for the binding of a series of inhibitors (carbon monoxide, methyl isocyanide) to the metallo-catalytic site of the MoFe protein, and the onset of catalytic transformation of alternative substrates (protons and acetylene) by the enzyme. Thus, we associate potentials with the redox levels for inhibition and catalysis by nitrogenase, with relevance to the elusive mechanism of biological nitrogen fixation.

Templated synthesis is an intriguing strategy for the length-controlled synthesis of oligomers. Traditionally, such reactions require stoichiometric amounts of the template with respect to the product. Recently we reported catalytic macrocyclic templates that promote oligomerization of a small molecule substrate with a remarkable degree of length control. Herein we present our efforts toward creating linear templates for catalytic length-controlled oligomer synthesis.

With the increase in the greenhouse effect and reduction of fossil fuel resources, it is urgent to find a feasible solution to directly convert power to chemicals using renewable energy and achieving zero carbon emissions targets. It is necessary to convert renewable energy (i.e., solar, wind, water, etc.) into electrical power replacing fossil-fuel-fired power. Therefore, the power-to-chemicals approach is gaining more and more attention. In the past two decades, non-thermal plasma, electro-catalysis, photo-catalysis, and their hybrid approaches have shown great potential for the power-to-chemicals solution. This paper introduces the application of plasma technology in energy conversion, focusing on three main routes for plasma-enabled ammonia synthesis, and analyses the state-of-the-art. Research results of ammonia synthesis based on plasma technology are discussed. The application of advanced in situ diagnostics evidences the importance of specific intermediate species and reaction pathways. Electrons, vibrationally-excited species, free radicals, and surface-adsorbed species play important roles in plasma-catalytic ammonia synthesis. Combined with experiments and simulations, the mechanisms of plasma-catalytic ammonia synthesis are examined. Vibrationally-excited species can effectively reduce the catalytic surface energy barrier. The techno-economics of the plasma-enabled ammonia synthesis technology is discussed in view of its competitive advantages. It is emphasized that the power-to-chemicals approach can be adapted for most chemical manufacturers, and these methods would play crucial roles in reducing carbon emissions and environmental pollution. Finally, suggestions are provided for the sustainable development of the power-to-chemicals industry in the future.

Photoredox catalysis is a valuable tool in a large variety of chemical reactions. Main challenges still to be overcome are photodegradation of photocatalysts and substrates, short lifetimes of reactive intermediates, and selectivity issues due to unwanted side reactions. A potential solution to these challenges is the pre-organization of the photosensitizer, substrate and (co)-catalyst in supramolecular self-assembled structures. In such architectures, (organic) dyes can be stabilized, and higher selectivity could potentially be achieved through pre-organizing desired reaction partners via non-covalent interactions. Perylene diimide (PDI) is an organic dye, which can be readily reduced to its mono- and dianion. Excitation of both anions leads to highly reducing excited states, which are able to reduce a variety of substrates via single electron transfer. The incorporation of PDI into a heteroleptic [M₄L^a₂L^b₂] supramolecular square has been recently demonstrated. Herein we investigate its photophysical properties and demonstrate that incorporated PDI indeed features photocatalytic activity. Initial results suggest that the pre-organisation by binding positively affects the outcome.