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Direct fuel cells such as those fed with ethanol (DEFCs) that employ anion exchange membranes can use non-platinum catalysts, which greatly reduces their system costs. In this study, we describe a passive air-breathing monoplanar alkaline DEFC equipped with a nanostructured carbon-supported anode (Pd) and cathode (FeCo) electrocatalysts. This DEFC was able to supply up to 30 mW cm-2 of peak electrical power density and was able to provide an almost constant amount of power at 1 mA cm-2 load for 3 months at room temperature. After such long periods of functioning at constant load, no degradation (physical or electrochemical) of the Pd-based anode catalyst was observed.

One of the biggest obstacles to the diffusion of fuel cells is their cost, a large part of which is due to platinum (Pt) electrocatalysts. Complete removal of Pt is a difficult if not impossible task for proton exchange membrane fuel cells (PEM-FCs). The Anion Exchange Membrane Fuel Cell > (AEM-FC) has long been proposed as a solution as non-Pt metals may be employed. Despite this, few examples of Pt free AEM-FCs have been demonstrated with modest power output. The main obstacle preventing the realization of a high power density Pt free AEM-FC is sluggish hydrogen oxidation (HOR) kinetics of the anode catalyst. In this presentation we describe a Pt free AEM-FC that employs a mixed carbon-CeO2 supported palladium (Pd) anode catalyst that exhibits enhanced kinetics for the HOR. AEM-FC tests run on dry H2 and pure air show peak power densities of more than 500 mW cm-2. We have investigated the origin of this remarkable performance using cyclic voltammetry (CV), HR-TEM/STEM as well as XAS. This analysis shows the improvement is due to a strong interaction between Pd and CeO2. This talk describes a careful morphological analysis that attests to a fine dispersion of the Pd nanoparticles accumulated mostly on the ceria part of the catalyst. Such a structure helps to weaken the Pd-H bonds and assists in supplying OHad from oxophilic CeO2 to the Pd-Had (HOR reaction sites), thus accelerating the overall HOR.

The electroreduction of CO2 is one of the most promising strategies for the production of fuels, energy vectors, and chemicals from CO2. Recently, we have described the realization of an electrochemical reactor based on the use of a Cu cathode for the CO2 electroreduction reaction. Here, three Cu electrodes were prepared by different techniques that generate different surface structures and morphologies. These three Cu cathodes, employed in the electrolysis cell, are compared in terms of Faradaic efficiency (FE) and product selectivity to a reference Cu foil electrode. The higher active surface area of these samples produced an improved total FE versus the Cu smooth plate. In terms of product selectivity, Cu electroplating onto a Cu foil enhanced HCOOK production strongly; the electrofaceting treatment of the Cu foil drove selectivity towards the production of CH4. In the third electrode, the deposition of Cu onto carbon cloth favors the formation of C2H4.

Copper sulfide (CuS) thin films were grown on a single crystal Ag(1 1 1) substrate by Electrochemical Atomic Layer Deposition (ECALD) method, i.e., by alternated surface limited deposition of copper and sulfur. A detailed investigation of deposition of Cu on S allowed to find the best conditions for copper deposition. The electrochemical characterization of deposits obtained with different deposition cycles suggests a 1:1 stoichiometric ratio between Cu and S corresponding to Cu monosulfide. The compositional analysis was performed by X-rays Photoelectron Spectroscopy (XPS), and the morphological was investigated by Atomic Force Microscopy (AFM) for deposits formed with 20 ECALD cycles.

The impregnation of Ketjen Black (C) with iron and cobalt phthalocyanines ( MPc ) taken one by one or as a 1:1 stoichiometric mixture, followed by heat treatment at 600 °C under inert atmosphere, gave materials containing arrays of single metal ions coordinated by four nitrogen atoms (M-N 4 units). Increasing the pyrolysis temperature to 800° resulted in the formation of carbon-supported, nanosized metal particles. A key role of the carbon support in determining the material structure at either temperature investigated was demonstrated by TPD, EXAFS, XANES and XRPD studies. These also showed that a Fe–Co alloy is obtained at 800 °C when the impregnation of Ketjen Black involves a mixture of FePc and CoPc . Electrodes coated with the different Fe, Co and Fe–Co materials, containing ca. 3 wt% metal loadings, were scrutinized for the oxygen reduction reaction (ORR) in alkaline media by linear sweep voltammetry. For comparative purposes, two Pt electrocatalysts containing 3 and 20 wt% metal were investigated. The electrochemical activity of all materials was analyzed by Tafel and Koutecky–Levich plots as well as chronopotentiometry. The Fe-containing electrocatalysts have been found to be highly active for the ORR in alkaline media with convective limiting currents as high as 600 A g Fe −1 at room temperature and onset potentials as high as 1.02 V vs. RHE. It has been found that (i) the ORR mass activity of the Pc -derived electrocatalysts is superior to that of the Pt catalysts investigated; (ii) the activity of FePc and FePc–CoPc/C , heat treated at either 600 or 800 °C, is superior to that of the corresponding Co materials; (iii) the electrocatalysts obtained at 600 °C are fairly more active than those obtained at 800 °C.

This article describes the development of a high power density Direct Formate Fuel Cell (DFFC) fed with potassium formate (KCOOH). The membrane electrode assembly (MEA) contains no platinum metal. The cathode catalyst is FeCo/C combined with a commercial anion exchange membrane (AEM). To enhance the power output and energy efficiency we have employed a nanostructured Pd/C-CeO2 anode catalyst. The activity for the formate oxidation reaction (FOR) is enhanced when compared to a Pd/C catalyst with the same Pd loading. Fuel cell tests at 60 °C show a peak power density of almost 250 mW cm−2. The discharge energy (14 kJ), faradic efficiency (89%) and energy efficiency (46%) were determined for a single fuel charge (30 mL of 4 M KCOOH and 4 M KOH). Energy analysis demonstrates that removal of the expensive KOH electrolyte is essential for the future development of these devices. To compensate we apply for the first time a polymeric ionomer in the catalyst layer of the anode electrode. A homopolymer is synthesized by the radical polymerization of vinyl benzene chloride followed by amination with 1,4-diazabicyclo[2.2.2]octane (DABCO). The energy delivered, energy efficiency and fuel consumption efficiency of DFFCs fed with 4 M KCOOH are doubled with the use of the ionomer.

The synthesis of nanostructures is an emerging area in nanoscience and technology with the possibility of numerous applications in micro and nanodevices. Confined electrodeposition can be achieved through the use of suitable templates, by which the electrodeposition occurs in natural or artificial holes of an insulating layer on a conducting substrate. Here, we present a procedure based on the selective desorption of 3-mercaptopropionic acid (MPA) from a mixture with 1-dodecanethiols (DDT) that forms a compact SAM on Ag(1 1 1). The compound grown is CdS, whose experimental growth conditions are simple and reproducible and make it a good “electrodeposition probe”.

The combination of the d(8) Rh(I) diolefin amide [Rh(trop(2)N)(PPh(3))] (trop(2)N=bis(5-H-dibenzo[a,d]cyclohepten-5-yl)amide) and a palladium heterogeneous catalyst results in the formation of a superior catalyst system for the dehydrogenative coupling of alcohols. The overall process represents a mild and direct method for the synthesis of aromatic and heteroaromatic carboxylic acids for which inactivated olefins can be used as hydrogen acceptors. Allyl alcohols are also applicable to this coupling reaction and provide the corresponding saturated aliphatic carboxylic acids. This transformation has been found to be very efficient in the presence of silica-supported palladium nanoparticles. The dehydrogenation of benzyl alcohol by the rhodium amide, [Rh]N, follows the well established mechanism of metal-ligand bifunctional catalysis. The resulting amino hydride complex, [RhH]NH, transfers a H(2) molecule to the Pd nanoparticles, which, in turn, deliver hydrogen to the inactivated alkene. Thus a domino catalytic reaction is developed which promotes the reaction R-CH(2)-OH+NaOH+2 alkene-->R-COONa+2 alkane.

The selective conversion of ethanol into potassium acetate with concomitant production of electrical energy has been achieved in both passive and active direct fuel cells containing platinum-free electrodes and an anion-exchange polymer membrane. The power densities supplied by the passive systems at r.t. can be as high as 55 mW cm−2, while the active systems can deliver up to 170 mW cm−2 at 80 °C. Such high values have never been reported for direct ethanol fuel cells with whatsoever electrocatalyst in either alkaline or acidic media. Keywords: Ethanol oxidation, Direct alcohol fuel cell, Acetic acid, Palladium, Anion-exchange polymer membrane

Solution multinuclear and multidimensional NMR analyses of the [(triphos)Rh(η1:η2-P4RR′)]n+ complex cations [triphos = MeC(CH2PPh2)3; R = H, Me, Ph; R′ = lone pair, H, Me; n = 0, 1] confirm the same primary structure determined by X-rays in the solid state. In addition, 2D 1H NOESY and 31P{1H} exchange NMR spectroscopy show that these complexes are nonrigid on the NMR time-scale over the 253–318 K temperature range. A dynamic process that involves the terminal phosphane groups of the triphos ligand is displayed by each compound. The NMR spectroscopic data indicate a slow scrambling motion in which the P4R unit tumbles with respect to the (triphos)Rh moiety. DFT calculations outline a possible turnstile mechanism involving the threefold and twofold rotors into which the complex is subdivided. The process goes through a transition state in which the axial and equatorial dispositions of the PRR′ and P=P donating groups of the P4RR′ ligand are inverted with respect to the ground state. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

On activation by MAO, tetrahedral Co II dichloride complexes supported by 6-organyl-2-(imino)pyridine ligands generate active catalysts for the dimerisation of propylene to hexenes. The nature of the substituent on the 6-position of the pyridine ring influences both the selectivity and activity of the catalysts. The 6-thienyl complexes CoCl 2 N 2 2Th and CoCl 2 N 2 2BT dimerise propylene prevalently to linear hexenes through a propagation pathway involving 1,2-insertion into Co-H, followed by 2,1-insertion and β-hydride elimination. The 6-phenyl complex CoCl 2 N 2 Ph is much less active and selective producing linear hexenes and methyl branched pentenes in comparable yields. The same activity trend and selectivity is observed for the dimerisation of 1-hexene, which however is one order of magnitude slower as compared to the dimerisation of propylene.

The position of the sulfur atom in the thienyl group of 6-(thienyl)-2-(imino)pyridine ligands strongly affects the catalytic activity of the corresponding tetrahedral high-spin dihalide CoII complexes in the oligomerization of ethylene to -olefins upon activation with methylaluminoxane (MAO). Complexes with the sulfur atom in the 3-position of the thienyl ring catalyze the selective conversion of ethylene to 1-butene, while catalysts containing thien-2-yl groups give C4 C14 alfa-olefins. In situ EPR experiments showed the occurrence of a spin state changeover with the formation of low-spin CoII species upon activation of the catalyst precursors by MAO. DFT calculations suggest that only thien-2-yl rings allow for the coordination of the sulfur atom to the cobalt center in the MAO-activated systems.

The electrooxidation of ethylene glycol (EG) and glycerol (G) has been studied: in alkaline media, in passive as well as active direct ethylene glycol fuel cells (DEGFCs), and in direct glycerol fuel cells (DGFCs) containing Pd-(Ni-Zn)/C as an anode electrocatalyst, that is, Pd nanoparticles supported on a Ni-Zn phase. For comparison, an anode electrocatalyst containing Pd nanoparticles (Pd/C) has been also investigated. The oxidation of EG and G has primarily been investigated in half cells. The results obtained have highlighted the excellent electrocatalytic activity of Pd-(Ni-Zn)/C in terms of peak current density, which is as high as 3300 A g(Pd)(-1) for EG and 2150 A g(Pd)(-1) for G. Membrane-electrode assemblies (MEA) have been fabricated using Pd-(Ni-Zn)/C anodes, proprietary Fe-Co/C cathodes, and Tokuyama A-201 anion-exchange membranes. The MEA performance has been evaluated in either passive or active cells fed with aqueous solutions of 5 wt % EG and 5 wt % G. In view of the peak-power densities obtained in the temperature range from 20 to 80 °C, at Pd loadings as low as 1 mg cm(-2) at the anode, these results show that Pd-(Ni-Zn)/C can be classified amongst the best performing electrocatalysts ever reported for EG and G oxidation.

The catalytic activation of polycrystalline platinum toward ethanol electro-oxidation in alkaline environment has been obtained by a square wave potential treatment. A detailed analysis that explores the effect of the period of the square wave on the evolution of the catalytic properties of the Pt surface is reported. The catalytic behavior of the treated and untreated surfaces has been interpreted both in terms of real surface area and surface structure evolution. The most active surface has been produced with a treating period time of 120 min. Interestingly the maximum stability has been obtained with the sample produced with square wave potential with a period of 360 min with slightly lower initial performance. We have also found that the treated samples limit C C cleavage, as compared to bare Pt, offering an effective strategy to minimize the formation of CO. Via in situ FTIR we have demonstrated that the major oxidation product is acetate. These findings are especially important in view of the application of Pt as a catalyst in alkaline direct ethanol fuel cells.

Half-cell reactions and alkaline direct ethylene glycol and glycerol fuel cells (DEGFC and DGFC) have been studied on Pd-based ternary core-shell (FeCo@Fe@Pd) nanocatalyst using multi-walled carbon nanotubes bearing carboxylic (MWCNT-COOH) and sulfonic acid (MWCNT-SO3H) as supporting platforms. The core-shell-shell nature of this nanocatalyst, obtained via the "microwave-induced top-down nanostructuring and decoration", was clearly proven from atomic resolution transmission electron microscopy (ARTEM). The functional groups of the MWCNTs show a huge impact on the physico-chemical properties of the FeCo@Fe@Pd nanocatalyst towards the electrocatalytic oxidation of EG and GLY in alkaline media. The FeCo@Fe@Pd on -COOH-treated MWCNTs showed the small particle size of ca. 7.4 nm, uniform loading of the catalyst on the support, large electrochemically-active surface area and enhanced electrocatalytic activity compared to the FeCo@Fe@Pd on -SO3H-bearing MWCNTs. As a preliminary test, FeCo@Fe@Pd/MWCNT-COOH was used for passive, air-breathing anion-exchange membrane based fuel cells (AEM-DEGFC and AEM-DGFC). The analysis of the exhaust products, established using NMR spectroscopy, revealed a high selectivity towards the complete oxidation of both EG and GLY under benign experimental conditions. This journal is

Direct alkaline ethanol fuel cells (DEFCs) are usually run with Pd anodic catalysts, but their performance can be improved by utilizing alloys of Pd and Co. The oxyphilic Co serves to supply ample -OH to the ethanol oxidation reaction, accelerating the rate limiting step at low overpotential under alkaline conditions. Pd-Co films with compositions between 20 and 80 at% Co can be prepared by electrodeposition from a NH3 complexing electrolyte. Cyclic voltammetry studies show that the ethanol oxidation peak exhibits increasing current density with increasing Co content, reaching a maximum at 77% Co. In contrast, potentiostatic measurements under conditions closer to fuel cell operating conditions show that a 50 at% Co alloy has the highest performance. Importantly, the Co-Pd film is also found to undergo phase and morphological transformations during ethanol oxidation, resulting in a change from a compact film to high surface area flake-like structures containing Co3O4 and CoOOH; such a transformation instead is not observed when operating at a constant potential of 0.7 VRHE.

Deactivation is one the main causes still preventing the full exploitation of palladium electrocatalysts in alkaline direct alcohol fuel cells and the electrochemical reforming of alcohols. While often attributed to the adsorption of poisoning species generated in the alcohols oxidation, in the present work we demonstrate that deactivation is provoked by the formation of palladium oxides. A combined approach including i) fuel cell runs, ii) cyclic voltammetry and iii) near edge X-ray absorption spectroscopy has enabled us to draw the conclusions reported in the paper.

A 2 μm thick layer of TiO2 nanotube arrays was prepared on the surface of the Ti fibers of a nonwoven web electrode. After it was doped with Pd nanoparticles (1.5 mgPd cm(-2) ), this anode was employed in a direct alcohol fuel cell. Peak power densities of 210, 170, and 160 mW cm(-2) at 80 °C were produced if the cell was fed with 10 wt % aqueous solutions of ethanol, ethylene glycol, and glycerol, respectively, in 2 M aqueous KOH. The Pd loading of the anode was increased to 6 mg cm(-2) by combining four single electrodes to produce a maximum peak power density with ethanol at 80 °C of 335 mW cm(-2) . Such high power densities result from a combination of the open 3 D structure of the anode electrode and the high electrochemically active surface area of the Pd catalyst, which promote very fast kinetics for alcohol electro-oxidation. The peak power and current densities obtained with ethanol at 80 °C approach the output of H2 -fed proton exchange membrane fuel cells.

A new azamacrocycle phosphonate in its hydrocloride form (1) has been synthesized and characterised by multinuclear NMR spectroscopy and by a single X-ray analysis. The reaction of 1 with CuII ions gives a polymeric compound (2), which exhibits an unprecedented three-dimensional network containing two-dimensional channels filled with guest molecules. The solid-state structure of 2 and its properties have been characterised by means of various analytical methods which include single-crystal X-ray structure analysis, X-ray powder diffraction, thermogravimetric studies as well as magnetic susceptibility and EPR measurements. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

The hydrogenation of thiophenes, leading to cyclic thioethers, thiols or hydrocarbons and H 2 S, can be achieved by single-site metal catalysts in both homogeneous and heterogeneous phase. An overview of the processes that have provided useful mechanistic information on hydrodesulfurization catalysis, is presented and commented.

The cage-like water-soluble monodentate phosphine 1,3,5-triaza-7-phosphaadamantane (PTA) has received renewed interest in the recent literature due to its properties to solubilize transition metal complexes in aqueous phase. This property has allowed application of Rh, Ru and Pd-PTA complexes in aqueous phase or biphasic homogeneous catalysis, antitumoral tests (Ru- and Pt-PTA) and photoluminescence (Au-PTA). This paper reviews the synthesis and structural properties of PTA and derivatives, their transition metal complexes, catalytic, medicinal and photoluminescence uses.

Reactions of Zeise's salt (K[Pt(eta(2)-C2H4)Cl-3]) with oxidized phenanthroline ligands (1, 10-phenanthroline-5,6-dione, phedon, and 2,9-dimethyl-1,10-phenanthroline-5,6-dione, Me(2)phedon) are reported. Comparison with analogous reactions involving unoxidized phen (1,10-phenanthroline) and Me phen (2,9-dimethyl-1,10-phenanthroline) ligands indicates that these latter ligands are less capable to stabilize the five-coordinate species [PtCl2 (eta(2)-C2H4)(phenanthroline)] in which the phenanthroline and the olefin share the trigonal plane and two chlorines are in the axial positions. The X-ray structure of the four-coordinate species [PtCl)(Me(2)phedon)] indicates that the major difference between oxidized and unoxidized phenanthrolines is the loss of aromaticity of the central ring of phenanthroline. As a consequence, the oxidized phenanthroline becomes more flexible and can undergo a bowlike distortion so to reduce steric interaction between ortho substituents of phenanthroline and cis chlorine ligands. The increase in stability of the four-coordinate species with Me(2)phedon is concomitant with an increase in stability of the five-coordinate precursor complex with ethylene. In the latter case the stabilization is not of sterical origin but stems from reduced electron-donor properties of oxidized phenanthrolines. The balance of the two effects is such that the equilibrium between five- and four-coordinate species is more shifted in favour of the former species in the case of Me2phedon than in the case of Me(2)phen.

Thermal reaction of white phosphorus with [(triphos)RhH(3)] (1) in THF affords [(triphos)Rh(eta(1):eta(2)-P(4)H)] (2), triphos=MeC(CH(2)PPh(2))(3). Similar complexes [(triphos)Rh(eta(1):eta(2)-P(4)R)] (R=Me (7), Et (8), Ph (9)) also form at lower temperature by the reaction of P(4) and [(triphos)Rh(R)(eta(2)-C(2)H(4))] with elimination of ethene. In contrast, a double-insertion process follows the reaction of [(triphos)Rh(H)(eta(2)-C(2)H(4))] and P(4) to generate tetraphosphido ethyl complex 8. Compounds 2, 7, 8 and 9 are thermally unstable and eventually decompose into the cyclotriphosphorus complex [(triphos)Rh(eta(3)-P(3))] (3) plus other unidentified phosphorus-containing species. Otherwise, PH(3) or PH(2)R is generated in the presence of H(2). The formation of PH(3) and 3 is quantitative starting from the precursor 2. The electrophilic attack of MeOTf or HBF(4) on the P(4)R ligand in the complexes 2, 7-9 is regioselective, and yields a cationic product of formula [(triphos)Rh(eta(1):eta(2)-P(4)RR')](+). The direct attack on the substituted p-R phosphorus atom is demonstrated by crossing experiments. Complexes of the latter type have been isolated in the solid state for the combinations R=H and R'=Me (11) or R=Ph and R'=Me (12). The latter species, [(triphos)Rh(eta(1):eta(2)-P(4)PhMe')]OTf.2 CH(2)Cl(2) (OTf=triflate), has been characterised by X-ray methods. The geometry at the metal is better described as a trigonal bipyramidal than pseudo-octahedral. In fact, the P(4)RR' unit acts as a bidentate ligand with its exocyclic PR(2) donor group and the endocyclic, dihapto-coordinated Pdbond;P linkage. The latter group lies in the equatorial plane, in a similar way to a classic olefin ligand that is coordinated to a butterfly-shaped L(4)M fragment (M=d(8)). DFT calculations on a model of 2 and all possible protonated isomers confirm that double substitution at the exocyclic P-donor positions of the open P(4) unit is energetically favoured. A multinuclear and multidimensional NMR analysis confirms that this structure is maintained in solution for both the parent and the protonated compounds.

In comparison with the separate components, the combination on the same support material of dispersed palladium nanoparticles and grafted molecular rhodium complexes has provided evidence of improved activity in the hydrogenation of arenes. It has been proposed that the catalytic efficiency is occasioned by a hydrogen-spillover process that would enhance specifically the hydrogenation activity of the molecular catalyst. A recent study of the hydrogenation of arenes with a catalyst obtained by silica sol-gel co-entrapment of metallic palladium and [Rh(cod)(m-Cl)]2 disagreed with the hydrogen spill-over hypothesis and suggested “the action of both metals, between which a kind of synergism exists”.2 No explanation on the nature of this synergism was provided, however. In this paper, we provide a rationale for this synergic effect, which involves partial inhibition by the tethered molecular complex of cyclic diene dehydrogenation occurring over the supported Pd(0) nanoparticles.

Hyperbranched (HB) aromatic polyamides (aramids), synthesized from A 2 + B 3 reagents (A = p-phenylenediamine; B = trimesic acid), have been used as polymeric supports for palladium(0) nanoparticles. The chemical-physical properties of these aramids, denoted as pPDT, have been compared to those of the polymer pABZAIA obtained from the AB 2 monomer 5-(4-aminobenzamido)isophthalic acid. The two HB polymers show structural differences in the shape of the macromolecule as well as the nature of the end groups. The pPDT materials exhibit a less regular structure with both amino and carboxy terminal groups, while the pABZAIA polymer contains a single amine focal unit per molecule and carboxy end groups. HB aramid-supported Pd° nanoparticles were obtained by reduction of polymer-supported PdCl 2 with an aqueous solution of NaBH 4 . Some model compounds, mimicking the polymeric hyperbranched structure, were investigated to gain insight into the nature of the interactions occurring between PdCl 2 and the support. The nature of the interactions between the polymeric matrix and PdCl 2 was investigated by means of FT IR and XPS techniques. XPS spectroscopy, performed on both polymers and model molecules, indicated that the interaction between the support and the metallic precursor involves the terminal amino groups. The particle dimensions and the metallic dispersion were determined by TEM analysis. This study showed that the dimensions and dispersion of the metal clusters on pABZAIA are smaller than those on pPDT. A preliminary study of the catalytic performance of a specific Pd°/ pPDT catalyst in the hydrogenation of relevant unsaturated substrates (benzene, benzylideneacetone, phenylacetylene, diphenylacetylene, and quinoline) has been carried out in either nonpolar or polar solvents. In most cases, the catalyst proved to be efficient, selective, and recyclable, yet the nature of the solvent affected remarkably the catalysis outcome in terms of both activity and selectivity.

A new potentially hexadentate tetraazamacrocycle based on the cyclen skeleton has been synthesized and fully characterized. The macrocycle 4,10-dimethyl-1,4,7,10-tetraazacyclododecane-1,7-bis(methanephosphonic acid monoethyl ester) dipotassium salt (Me2DO2PME) contains mutually trans monoethyl ester phosphonate acid substituents on two nitrogen atoms, and trans methyl substituents on the other two nitrogen atoms. The protonation constants of this macrocycle and the stability constants of its complexes with Cu2+, Zn2+, Gd3+ and Ca2+ ions have been determined by pH potentiometric titrations. The protonation sequence of the macrocycle has been studied by 1H, 31P[1H] and 13C[1H] NMR spectroscopy: the first and second protonation steps take place at the methyl-substituted nitrogen atoms, while the third protonation involves one oxygen from a phosphonate group. Upon protonation, all the CH2 ring protons become magnetically inequivalent on the NMR time scale due to a slow conformational rearrangement, most likely occasioned by the formation of multiple hydrogen bonds within the macrocyclic ring. Me2DOPM forms neutral, mononuclear complexes with all the metals investigated. The presence of hydroxo complexes was observed for Ca2+ and Zn2+ at high pH values. Structural information on the neutral complex [Cu(Me2DO2PME)] has been obtained by a solution X-Band EPR study. It is proposed that Me2DO2PME binds Cu2+ in a distorted octahedral structure using all of its donor atoms, i.e. the four nitrogen atoms and the two phosphonate oxygen atoms. The redox chemistry of [Cu(Me2DO2PME)] in dimethyl sulfoxide and water has been studied by electrochemical measurements. Cyclic voltammetry in DMSO shows the complex to undergo a quasireversible one-electron reduction step leading to an unstable CuI species.

A comparative study of the hydrogenation of various heterocycles, model compounds in raw oil materials, by either Ru(II) complex immobilized on mesoporous silica or Ru(0) nanoparticles deposited on the same support has been performed. The single-site catalyst contains the molecular precursor [Ru(NCMe)3(sulphos)](OSO2CF3) tethered to partially dehydroxylated high-surface-area silica through hydrogen bonds between silanol groups of the support and SO3− groups from both the sulphos ligand [−O3S(C6H4)CH2C(CH2PPh2)3] and the triflate counter anion. Highly dispersed ruthenium nanoparticles were prepared by calcination/reduction of silica-supported Ru3(CO)12. The heterocycles (benzo[b]thiophene, quinoline, indole, acridine) are hydrogenated to cyclic thioethers or amines. The Ru(II) single-site catalyst is active for both benzo[b]thiophene and the N-heterocycles, while the Ru(0) catalyst does not hydrogenate the S-heterocycle, yet is efficient for the reduction of the N-heterocycles and simple aromatic hydrocarbons. The surface silanols promote the hydrogenation of indole via NH⋯ O(H)Si hydrogen bonds and can interact with the π-electron density of all substrates.

Mercury-supported, self-assembled monolayers of the sole (SAMs) dioleoylphosphatidylcholine (DOPC)and of a raft -forming mixture of DOPC, cholesterol (Chol) and palmitoylsphingomyelin of (59:26:15) mol% composition(PSM) , were investigated by electrochemical impedance spectroscopy (EIS), both in the absence and in the presence of the monosialoganglioside GM1. The impedance spectra of these four SAMs were fitted by a series of parallel combinations of a resistance and a capacitance ( RC meshes) and displayed on plots of ω Z ′ against −ω Z ″, where Z ′ and Z ″ are the in -phase and quadrature components of the impedance and is the angular frequency. A comparison among these ωdifferent impedance spectra points to the formation of GM1-rich gel phase microdomains within the lipid rafts of the DOPC/Chol/PSM mixture, thanks to the unique molecular-level smooth support provided by mercury, whichallows EIS to detect the protruding gel phase microdomains by averaging them over a macroscopically large area.

The energetic convenience of electrolytic water splitting is limited by thermodynamics. Consequently, significant levels of hydrogen production can only be obtained with an electrical energy consumption exceeding 45 kWh kg(-1)H2. Electrochemical reforming allows the overcoming of such thermodynamic limitations by replacing oxygen evolution with the oxidation of biomass-derived alcohols. Here we show that the use of an original anode material consisting of palladium nanoparticles deposited on to a three-dimensional architecture of titania nanotubes allows electrical energy savings up to 26.5 kWh kg(-1)H2 as compared with proton electrolyte membrane water electrolysis. A net energy analysis shows that for bio-ethanol with energy return of the invested energy larger than 5.1 (for example, cellulose), the electrochemical reforming energy balance is advantageous over proton electrolyte membrane water electrolysis.

The electrocatalytic properties of small amounts of silver (3-17 ?g cm-2) electrodeposited on glassy carbon can be sensibly increased by an activation protocol based on pretreatment oxidation/reduction cycles that produces significant changes in particle's morphology. The catalytic effects on both Oxygen Evolution Reaction (OER) and Oxygen Reduction Reaction (ORR) are evaluated by the onset potentials of the voltammetric curves, and the number of electrons involved in ORR is evaluated by the Levich plot. Tafel plots of both OER and ORR curves obtained after the activation protocol show significant changes that rule out the hypothesis that the catalytic effect could only be attributed to an increased roughness of the samples. Furthermore, the electrochemically active surface area of silver, as measured by the charge involved in Pb underpotential deposition, was found to increase linearly with the amount of depositing silver. On the contrary, the Tafel plots of increasing amounts of silver show that the increase of the catalytic effect with silver loading is not linear as expected in a mere increase of the roughness factor. Levich-Koutecky and Tafel plots evidenced that the highest silver loading showed a catalytic effect greater than that expected on the basis of the electrochemically active surface area. © 2014 The Electrochemical Society.

The selective production of chemicals from renewable resources with contemporaneous release of energy is perhaps one of the most desired targets of sustainable chemistry. Here, we report an overview of our recent research efforts, where we have demonstrated that this can be achieved using renewable alcohols, by means of two electrochemical devices: direct fuel cells and electrolyzers. In either case, an aqueous solution of the fuel in the anode compartment is oxidized on a nanostructured electrocatalyst that promotes selectively the partial oxidation of the anolyte with high stability and fast kinetics. We have found that anode electrocatalysts based on nanosized Pd particles, alone or promoted by Ni-Zn phases as well as by CeO2 or TiO2, are able to accomplish this goal in alkaline environment when used in conjunction with commercially available cathode electrocatalysts and solid or liquid electrolytes. In an electrolyzer, containing an anode electrocatalyst similar to that employable in a DAFC, the electrolyte may be either an anion exchange-membrane or a solution of an alkali metal hydroxide (NaOH or KOH, for example) and the alcohol is converted to the corresponding alkali metal carboxylate, while hydrogen gas is produced at the cathode upon water reduction. © 2014 The Electrochemical Society. [DOI: 10.1149/2.005407jes] All rights reserved.

As part of our modelling studies of the hydrodenitrogenation of N-heterocycles contained in raw oil materials, we investigated the selective hydrogenation of quinoline to 1,2,3,4-tetrahydroquinoline by rhodium catalysts modified with the tripodal polyphosphane ligand MeC(CH2PPh2)3. Experiments in standard autoclaves and in high-pressure sapphire NMR tubes, kinetic and isotope labelling studies, and independent reactions with isolated compounds have contributed to the elucidation of the catalytic mechanism as well as identification of the electronic requisites of the metal catalyst for selective and efficient hydrogenation.

Recent legislation directed at reducing nitrogen levels in fossil fuels has led to numerous studies of the hydrodenitrogenation (HDN) process, whereby nitrogen is removed from organic compounds in petroleum feedstocks. In this review a comprehensive study of the coordination, activation, hydro- genation, hydrogenolysis and denitrogenation of N-heterocycles assisted by transition metal complexes in either fluid solution or single-site systems, is reported. Furthermore, similarities to the reactions occurring in the HDN process over commercial heterogeneous catalysts are also discussed.

The Ru(II) complex [(sulphos)Ru(NCMe)3](OSO2CF3) (1) has been immobilized on partially dehydroxylated high-surface-area silica via hydrogen-bonding interactions between the silanol groups of the support and the SO3- groups from both the sulphos ligand and the triflate counteranion (sulphos = -O3S(C6H4)CH2C(CH2PPh2)3). Compound 1 has been authenticated in the solid state by a single-crystal X-ray analysis and in solution by NMR spectroscopy, while its silica-grafted form [(sulphos)Ru(NCMe)3](OSO2CF3)/SiO2 (1/SiO2) has been characterized by DRIFT and CP MAS 31P NMR studies. The supported hydrogen-bonded (SHB) complex 1/SiO2 is an effective and selective catalyst for the hydrogenation of benzylideneacetone to benzylacetone and of benzonitrile to benzylidenebenzylamine in n-octane. No appreciable ruthenium leaching into the hydrocarbon phase was observed in either case. Analogous hydrogenation reactions catalyzed by either the aqueous-biphase catalyst 1 in water/n-octane or the homogeneous analogue [(triphos)...

The hydroformylation of 1-hexene with syngas (40 bar of 1:1 CO/H2) in the presence of the catalyst precursor RhH(CO)(PPh3)3 has been studied by high-pressure NMR spectroscopy in a 10 mm sapphire tube equipped with a Ti-alloy valve. Except for RhH(CO)2(PPh3)2, no direct observation of labile intermediates involved in the catalytic cycle has been detected; however as many as four rhodium resting states have been seen, and some factors controlling their formation/interconversion/inhibition have been identified. The information gathered from this in situ investigation is particularly relevant to a better understanding of the inhibiting action of the CO pressure as well as the positive action of PPh3 addition.

The rhodium alkyl and aryl complexes [(triphos)Rh(R)(η2-C2H4)] (R = Me (1), Et (2), Ph (3); triphos = MeC(CH2PPh2)3) react with white phosphorus in THF at room temperature to give the new complexes [(triphos)Rh(η1:η2-P4R)] (R = Me (4), Et (5), Ph (6)). This reaction represents the first example in which a P−C bond is formed by starting from white phosphorus through the mediation of a transition-metal complex.

The ruthenium(II) tris-acetonitrile complex [(triphos)Ru(MeCN)3]BPh4 (1) is an extremely efficient catalyst precursor for the regioselective hydrogenation of benzo[b]thiophene (BT) to 2,3-dihydrobenzo[b]thiophene (DHBT) in homogeneous phase under mild reaction conditions (THF, 40−100 °C, 1−30 bar H2) [triphos = MeC(CH2PPh2)3]. At 30 bar of H2 and 100 °C, BT is converted to DHBT with an average rate of 500 mol of product (mol of cat)-1 h-1. During the catalytic reactions with PH2 > 5 bar, the acetonitrile ligands in 1 are transformed into a mixture of NHEt2, NEt3, and NH3, while the termination ruthenium products are the monohydrido complexes [(triphos)Ru(H)(NH3)2]BPh4, [(triphos)Ru(H)(NH3)(NH2Et)]BPh4, and [(triphos)Ru(H)(NH3)(η1-S-DHBT)]BPh4. Below 5 bar of H2, no hydrogenation of MeCN occurs and all of the ruthenium is recovered as [(triphos)Ru(H)(NCMe)(η1-S-DHBT)]BPh4. All of these Ru(II) hydrido complexes catalyze the hydrogenation of BT to DHBT as efficiently as 1. The substitution of D2 for H2 in a ...

In this work are described the syntheses of several new dppp-like ligands (dppp =1,3-bis(diphenylphosphino)propane) bearing different substituents on the carbon backbone and of their palladium(II) complexes with acetate or trifluoroacetate coligands (L). The complexes exhibit the general formula Pd(P−P)(L)2 and have been employed as catalyst precursors for the copolymerization of ethene and carbon monoxide in MeOH under experimental conditions that are comparable to those reported in the relevant literature and patents for dppp-based Pd(II) copolymerization catalysts. It has been found that the introduction of alkyl substituents in the 2-position of the carbon backbone of dppp does not significantly improve the performance of the corresponding catalyst precursors (highest productivity value 6.2 kg of copolymer (g of Pd h)-1 vs 5.4 kg of copolymer (g of Pd h)-1 for Pd(dppp)(L)2). In contrast, the productivity increases remarkably when methyl groups are introduced in both 1-positions of the diphosphine liga...

The heterogenization of the zwitterionic Rh(I) catalysts (sulfos)Rh(cod) (1) and (sulfos)Rh(CO)2 (2) [sulfos = -O3S(C6H4)CH2C(CH2PPh2)3; cod = cycloocta-1,5-diene] is performed by controlled adsorption on partially dehydroxylated high surface area silica. The immobilization procedure is based uniquely on the capability of the sulfonate tail of sulfos to link the silanol groups of the support via hydrogen bonding. Experimental evidence of the −SO3···HOSi− interaction between 1 or 2 and silica has been obtained from IR, Rh K-edge EXAFS, and CP MAS 31P NMR studies. The grafted catalyst (sulfos)Rh(cod)/SiO2 (1/SiO2) is active for the hydrogenation of alkenes in either flow reactors (ethene, propene) or batch reactors (styrene) in hydrocarbon solvents. The hydroformylation of alkenes, here exemplified by 1-hexene, is catalyzed exclusively in solid−liquid conditions. No Rh leaching is observed in either case. In solid−gas conditions, the catalyst 1/SiO2 is converted by syngas to the catalytically inactive, dica...

The water-soluble diphosphine (NaO3S(C6H4)CH2)2C(CH2PPh2)2 (Na2DPPPDS) was employed to prepare the bis-trifluoroacetate Pd(II) complex Pd(Na2DPPPDS)(CO2CF3)2·2THF (1). The catalytic performance of ...

Several bis-chelated palladium(II) complexes, [Pd(P-P)(N-N)x](PF6)2, containing binary combinations of diphosphine and dinitrogen ligands have been prepared and characterized. The diphosphine ligands comprise 1,3-bis(diphenylphosphino)propane (dppp), meso-2,4-bis(diphenylphosphino)pentane (meso-bdpp), rac-2,4-bis(diphenylphosphino)pentane (rac-bdpp) and 2,2′-bis(diphenylphosphinoethyl)pentane (Etdppp), while the dinitrogen ligands are either 2,2′-bipyridine (bipy; x=1) or 1,8-naphthyridine (napy; x=2). The structure of [Pd(meso-bdpp)(N,N′-bipy)](PF6)2·CH2Cl2 has been determined by an X-ray structural analysis. All the Pd(II) complexes have been tested as catalyst precursors for the copolymerization of carbon monoxide and ethene in methanol solution in either autoclaves or high-pressure sapphire NMR tubes. The combination of meso-bdpp and bipy at palladium, in conjuction with both 1,4-benzoquinone and p-toluenesulfonic acid, has shown the best catalytic performance. The different catalytic activities exhibited by the stereoisomers [Pd(meso-bdpp)(N,N′-bipy)]- (PF6)2 and [Pd(rac-bdpp)(N,N′-bipy)](PF6)2 has been interpreted in terms of the different spatial distribution of the phenyl rings around the metal center determined by the conformation of the six-membered metallaring.

The reaction of [(triphos)RuH(BH4)] (1) in THF with KOBut yields the novel trihydride complex K[(triphos)RuH3] (2) and BH2OBut (triphos = MeC(CH2PPh2)3). The ruthenate complex 2 can also be synthesized by hydrogenation (30 bar of H2) in THF of the tris(acetonitrile) complex [(triphos)Ru(NCMe)3](BPh4)2 (3) in the presence of a 5-fold excess of BH2OBut at 40 °C. This reaction produces a mixture of NH2Et, NHEt2, NEt3, and NH3 as a result of MeCN hydrogenation, followed by amine redistribution reactions. Compound 2 is isolated in analytically pure form as [K(C12H24O6)][(triphos)RuH3] (2a) by recrystallization from THF/n-hexane in the presence of 18-crown-6 ether. In the presence of a strong base such as KOBut, both 1 and 3 are effective catalyst precursors for the homogeneous hydrogenolysis of benzo[b]thiophene (BT) to 2-ethylthiophenol (ETP) in THF under mild reaction conditions (≥70 °C, 30 bar of H2). The hydrogenolysis rate increases with the concentration of the base, which, depending on the catalyst prec...

The ruthenium(II) (tetrahydroborate)hydride complex [(triphos)RuH(BH4)] (1) reacts with benzo[b]thiophene (BT) in THF at 40 °C yielding, after 3 h, a mixture of four different compounds: [(triphos)RuH{BH3(o-S(C6H4)CH2CH3)}] (2), [(triphos)Ru{η4-S(C6H4)CH(CH3)}] (3), [(triphos)RuH(μ-S(C6H4)CH2CH3)2HRu(triphos)] (4), and [(triphos)RuH(μ-BH4)HRu(triphos)]+ (5+) (triphos = MeC(CH2PPh2)3). After two further hours of reaction, 3 disappears and is completely converted to 4. Further heating at 40 °C does not change the product composition (2, 4, and 5+ in a 4:1.3:3 ratio). A variety of independent reactions with isolated compounds have been performed with the aim of elucidating the mechanism of the C−S insertion/hydrogenation of BT to the 2-ethylthiophenolate ligand. The μ-thiolate complex 4 reacts in THF with dihydrogen (≥160 °C, 30 bar H2) or with HBF4·OEt2 (20 °C) yielding ethylbenzene and 2-ethylthiophenol, respectively. No reaction occurs with LiHBEt3. All of the reactions and new complexes reported have be...

The novel Ir(III) nonclassical tetrahydrido complex [(triphos)Ir(H(2))(H)(2)]BPh(4) (4BPh(4)) has been prepared by hydrogenation of the ethene dihydride complex [(triphos)Ir(C(2)H(4))(H)(2)]BPh(4) in either the solid state (P(H)()2/= 1 atm) or CH(2)Cl(2) solution (P(H)()2/= 3 atm) [triphos = MeC(CH(2)PPh(2))(3)]. Complex 4BPh(4)()()is very labile in solution and can be isolated in the solid state exclusively from solid-gas reactions. Characterization of 4BPh(4) in solution can be achieved( )()by high-pressure NMR and IR spectroscopies, however. Various deuterated isotopomers of [(triphos)Ir(H(2))(H)(2)](+) have been obtained in CD(2)Cl(2) solution at low temperature by treatment of the trihydride [(triphos)IrH(3)] with DOSO(2)CF(3). On the basis of a variety of NMR experiments, the complex cation [(triphos)Ir(H(2))(H)(2)](+) is assigned an octahedral structure where two terminal hydride ligands and a dihydrogen molecule are trans to the phosphorus atoms of a facial triphos ligand. Complex 4BPh(4)()()dissolves in THF at room temperature yielding [(triphos)IrH(3)], BPh(3), and benzene; a similar reaction occurs in acetone, whereas in CH(2)Cl(2) the complex loses H(2) converting to the dimers cis- and trans-[(triphos)IrH(mgr;-H)(2)HIr(triphos)](BPh(4))(2).

The rhodium-catalyzed hydroformylation of 1-hexene in THF with the linear triphosphane PhP(CH2CH2PPh2)2 [PP,] has been studied both in situ and in high-pressure autoclaves. Sapphire NMR tubes with titanium valves have proved useful for studying the in situ reactions under conditions of relatively high syngas pressure (30–90 atm H,/CO) and temperature (60–100 C). Under conditions conducive to effective hydroformylation, the catalyst precursor [ (PP,)Rh(CO)]+ is quantitatively converted to the dicarbonyl [ (PP,)Rh(CO),]+, which is also the termination product of the catalysis. Irrespective of the syngas composition and of the total pressure, the dicarbonyl complex is the only phosphorus-containing species detectable on the NMR time-scale during the course of the isomerization and hydroformylation of the alkene. The PP2-Rh catalytic system exhibits some peculiar features that may be summarized as follows. (i) Very high partial pressures of CO (120 atm) neither inhibit the hydroformylation nor affect the n/i selectivity; (ii) alkene hydrogenation occurs neither at very high partial pressures of H, (120 atm) nor in the absence of added CO; (iii) the isomerization rate is slightly faster than that of hydroformylation; (iv) terminal and internal alkenes (2-, 3-hexenes) are hydroformylated with comparable rates. Various control experiments have been carried out using in-situ NMR, as well as batch experiments under different reaction conditions or with different catalyst precursors. Despite these extensive studies, unambiguous conclusions about the catalysis mechanism have not been reached. In particular, the possibility that different catalysts may be operative depending on the reaction conditions cannot be ruled out. The hydroformylation results rule out the involvement of phosphane-free “Rh-CO” catalysts, even under conditions of very high partial pressure of CO, and point to “(PP,)Rh(CO),” catalysts with small steric hindrance over the whole range of syngas pressures investigated.

The catalytic activity of the zwitterionic complex [(sulphos)Rh(cod)] for the hydrogenation and hydrogenolysis reactions of benzo[b]thiophene (BT) has been studied in either methanol or liquid-biph...