Chemical, electrochemical and photochemical molecular water oxidation catalysts

Hydrogen release from the splitting of water by simply using sunlight as the only energy source is an old human dream that could finally become a reality. This process involves both the reduction and oxidation of water into hydrogen and oxygen, respectively. While the first process has been fairly overcome, the conversion of water into oxygen has been traditionally the bottleneck process hampering the development of a sustainable hydrogen production based on water splitting. Fortunately, a revolution in this field has occurred during the past decade, since many research groups have been conducting an intense research in this area. Thus, while molecular, well-characterized catalysts able to oxidize water were scarce just five years ago, now a wide range of transition metal based compounds has been reported as active catalysts for this transformation. This review reports the most prominent key advances in the field, covering either examples where the catalysis is triggered chemically, electrochemically or photochemicall

Grup de Recerca Catàlisi d'Oxidació Selectiva (SelOxCat)

La demanda energètica de les societats actuals és cada vegada més elevada, mentre que les reserves de combustibles d'origen no renovable, les més utilitzades, van minvant. En aquesta situació, la recerca de fonts d'energia renovables adquireix una importància rellevant. El grup de recerca SelOxCat (Catàlisid'Oxidació Selectiva) utilitza una àmplia gamma de tècniques per tal d'estudiar, comprendre i desenvolupar les reaccions principals per a la producció de combustibles renovables a partir d'aigua i llum solar.La demanda energética de las sociedades actuales es cada vez más elevada, mientras que las reservas de combustibles de origen no renovable, las más utilizadas, van disminuyendo. En esta situación, la búsqueda de fuentes de energía renovables adquiere una importancia relevante. El grupo de investigación SelOxCat (Catálisis de Oxidación Selectiva) utiliza una amplia gama de técnicas para estudiar, comprender y desarrollar las reacciones principales para la producción de combustibles renovables a partir de agua y luz solar.The energy demand of modern societies is increasingly high, while the reserves of non-renewable fuel sources, the most common, are diminishing. In this situation, the search for renewable energy sources acquires considerable importance. The SelOxCat research group uses a range of techniques to study, understand and develop the reactions leading to the production of renewable fuels from water and sunlight

Light-driven hydrogen evolution assisted by covalent organic frameworks

Altres ajuts: RSCCovalent organic frameworks (COFs) are crystalline porous organic polymers built from covalent organic blocks that can be photochemically active when incorporating organic semiconducting units, such as triazine rings or diacetylene bridges. The bandgap, charge separation capacity, porosity, wettability, and chemical stability of COFs can be tuned by properly choosing their constitutive building blocks, by extension of conjugation, by adjustment of the size and crystallinity of the pores, and by synthetic post-functionalization. This review focuses on the recent uses of COFs as photoactive platforms for the hydrogen evolution reaction (HER), in which usually metal nanoparticles (NPs) or metallic compounds (generally Pt-based) act as co-catalysts. The most promising COF-based photocatalytic HER systems will be discussed, and special emphasis will be placed on rationalizing their structure and light-harvesting properties in relation to their catalytic activity and stability under turnover conditions. Finally, the aspects that need to be improved in the coming years will be discussed, such as the degree of dispersibility in water, the global photocatalytic efficiency, and the robustness and stability of the hybrid systems, putting emphasis on both the COF and the metal co-catalyst

[1,9-Bis(3,5-di­methyl­pyrazol-1-yl-κN2)-3,7-di­thia­nonane-κ2S,S']­palladium(II) bis­(tetra­fluoro­borate)

In the crystal structure of the title compound, [Pd(C17H28N4S2)](BF4)2, the PdII atom is coordinated by one N atom from each of the pyrazolyl groups and the two thio¬ether S atoms in a slightly distorted square-planar geometry

Cyclobutane-based peptides/terpyridine conjugates : Their use in metal catalysis and as functional organogelators

Two new conjugates, hcptpyDP and hcptpyTP, of a terpyridine derivative incorporating artificial peptide moieties, have been synthesized and their use in the preparation of metal catalysts and organogelators has been investigated. Ru(II) complexes derived from these ligands showed electrochemical behavior and activity as catalysts in the epoxidation of olefins similar to that of Beller's catalyst. As organogelators, these conjugates were able to gelate a variety of solvents, from toluene to methanol, with satisfactory mgc (minimum gelation concentration) values. The presence of 4'-(4-carboxy)phenylterpyridine (hcptpy) moiety allows tuning the gelling properties and also influences the supramolecular self-assembling mode to produce chiral aggregates with respect to parent peptides DP and TP. In the case of the conjugates, π−π interactions provided by the aromatic moieties cooperate with inter-molecular hydrogen bonding between NH and CO in the amide groups. Further properties of peptide/terpyridine conjugates are under investigation in view of future applications

Organocatalytic vs. Ru-based electrochemical hydrogenation of nitrobenzene in competition with the hydrogen evolution reaction

The electrochemical reduction of organic contaminants allows their removal from water. In this contribution, the electrocatalytic hydrogenation of nitrobenzene is studied using both oxidized carbon fibres and ruthenium nanoparticles supported on unmodified carbon fibres as catalysts. The two systems produce azoxynitrobenzene as the main product, while aniline is only observed in minor quantities. Although PhNO2 hydrogenation is the favoured reaction, the hydrogen evolution reaction (HER) competes in both systems under catalytic conditions. H2 formation occurs in larger amounts when using the Ru nanoparticle based catalyst. While similar reaction outputs were observed for both catalytic systems, DFT calculations revealed some significant differences related to distinct interactions between the catalytic material and the organic substrates or products, which could pave the way for the design of new catalytic materials

Anàlisi de molècules molt eficients per millorar la síntesis orgànica

Mitjançant tècniques experimentals i informàtiques, els autors d'aquest treball van analitzar l'eficiència d'alguns grups de molècules, derivades de compostos de pirazol, usades com a precatalitzadors en els processos de síntesis orgàniques realitzats amb la reacció de Heck.A través de técnicas experimentales e informáticas, los autores de este trabajo analizaron la efectividad de algunos grupos de moléculas, derivados de compuestos de pirazol, usadas como precatalizadores en los procesos de síntesis orgánica realizados mediante la Reacción de Heck.Based on a combined experimental and computacional study, authors of this work analized the effectiveness of some groups of molecules derivated from pirazol, used as precatalists in organic synthesis developed by Heck reactions

Catalitzadors químics, electroquímics i fotoquímics de l'oxidació molecular de l'aigua

L'alliberament d'hidrogen a partir del trencament de l'aigua pel simple ús de la llum solar com a única font d'energia és un vell somni de la humanitat que finalment podria convertir-se en una realitat. Un article del grup de recerca SelOxCat informa dels avenços més destacats en aquest procés, que abasta l'estudi de l'oxidació catalítica de l'aigua mitjançant l'ús de compostos moleculars que contenen ions de metalls de transició, considerant exemples en què la catàlisi s'inicia químicament, electroquímicament i/o fotoquímicament

Unravelling the Mechanistic Pathway of the Hydrogen Evolution Reaction Driven by a Cobalt Catalyst

Acord transformatiu CRUE-CSICA cobalt complex bearing a κ-NP ligand is presented (1 or Co(L), where L is (1E,1'E)-1,1'-(pyridine-2,6-diyl)bis(N-(3-(diphenylphosphanyl)propyl)ethan-1-imine). Complex 1 is stable under air at oxidation state Co thanks to the π-acceptor character of the phosphine groups. Electrochemical behavior of 1 reveals a two-electron Co/Co oxidation process and an additional one-electron reduction, which leads to an enhancement in the current due to hydrogen evolution reaction (HER) at E=−1.6 V vs Fc/Fc. In the presence of 1 equiv of bis(trifluoromethane)sulfonimide, 1 forms the cobalt hydride derivative Co(L)-H (2), which has been fully characterized. Further addition of 1 equiv of CoCp* (Cp* is pentamethylcyclopentadienyl) affords the reduced Co(L)-H (2) species, which rapidly forms hydrogen and regenerates the initial Co(L) (1). The spectroscopic characterization of catalytic intermediates together with DFT calculations support an unusual bimolecular homolytic mechanism in the catalytic HER with 1

Surface-Functionalized Nanoparticles as Catalysts for Artificial Photosynthesis

Altres ajuts: acords transformatius de la UABAnalogously to enzymatic catalysis, where the active metal sites and their environment are controlled by protein residues, the catalytic properties of metal nanoparticles (NPs) can be tuned by carefully selecting their surface-coordinated species. In artificial photosynthesis, surface-functionalization emerged in the last decade, grounded on the development of reliable methods for tailored synthesis, advanced characterization and theoretical modeling of metal NPs, altogether with the aim of transferring to the nanoscale the mechanistic knowledge acquired from molecular complexes. Metal NPs surface-functionalization modulates the energetics of key catalytic intermediates, introduces second coordination sphere effects, influences the catalyst-electrolyte interface, and determines the metal NPs surface coverage and, accordingly, the number of accessible active sites. In photoactivated systems, metal NPs surface-functionalization may play a key role in modulating the charge transfers and recombination processes between the light absorber and the active sites and in the light absorber itself. Thus, after a presentation of the most relevant synthetic methods to produce well-defined surface-functionalized metal NPs, a critical analysis of why the above effects are the cornerstone in enhancing their catalytic performance in the key processes of artificial photosynthesis, namely the oxygen evolution reaction, the hydrogen evolution reaction, and the CO2 reduction reaction, is given