Werner Oberhauser

Ethanol Oxidation on Electrocatalysts Obtained by Spontaneous Deposition of Palladium onto Nickel-Zinc Materials

Ni-Zn and Ni-Zn-P alloys supported on Vulcan XC-72 are effective materials for the spontaneous deposition of palladium through redox transmetalation with Pd(IV) salts. The materials obtained, Pd-(Ni-Zn)/C and Pd-(Ni-Zn-P)/C, have been characterized by a variety of techniques. The analytical and spectroscopic data show that the surface of Pd-(Ni-Zn)/C and Pd-(Ni-Zn-P)/C contain very small, highly dispersed, and highly crystalline palladium clusters as well as single palladium sites, likely stabilized by interaction with oxygen atoms from Ni--O moieties. As a reference material, a nanostructured Pd/C material was prepared by reduction of an aqueous solution of PdCl(2)/HCl with ethylene glycol in the presence of Vulcan XC-72. In Pd/C, the Pd particles are larger, less dispersed, and much less crystalline. Glassy carbon electrodes coated with the Pd-(Ni-Zn)/C and Pd-(Ni-Zn-P)/C materials, containing very low Pd loadings (22-25 microg cm(-2)), were studied for the oxidation of ethanol in alkaline media in half cells and provided excellent results in terms of both specific current (as high as 3600 A g(Pd)(-1) at room temperature) and onset potential (as low as -0.6 V vs Ag/AgCl/KCl(sat)).

Nanotechnology makes biomass electrolysis more energy efficient than water electrolysis

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.

A comparison between silica-immobilized ruthenium(II) single sites and silica-supported ruthenium nanoparticles in the catalytic hydrogenation of model hetero- and polyaromatics contained in raw oil materials

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.

Energy Efficiency Enhancement of Ethanol Electrooxidation on Pd–CeO2/C in Passive and Active Polymer Electrolyte‐Membrane Fuel Cells

Pd nanoparticles have been generated by performing an electroless procedure on a mixed ceria (CeO(2))/carbon black (Vulcan XC-72) support. The resulting material, Pd-CeO(2)/C, has been characterized by means of transmission electron microscopy (TEM), inductively coupled plasma atomic emission spectroscopy (ICP-AES), and X-ray diffraction (XRD) techniques. Electrodes coated with Pd-CeO(2)/C have been scrutinized for the oxidation of ethanol in alkaline media in half cells as well as in passive and active direct ethanol fuel cells (DEFCs). Membrane electrode assemblies have been fabricated using Pd-CeO(2)/C anodes, proprietary Fe-Co cathodes, and Tokuyama anion-exchange membranes. The monoplanar passive and active DEFCs have been fed with aqueous solutions of 10 wt% ethanol and 2 M KOH, supplying power densities as high as 66 mW cm(-2) at 25 °C and 140 mW cm(-2) at 80 °C. A comparison with a standard anode electrocatalyst containing Pd nanoparticles (Pd/C) has shown that, at even metal loading and experimental conditions, the energy released by the cells with the Pd-CeO(2)/C electrocatalyst is twice as much as that supplied by the cells with the Pd/C electrocatalyst. A cyclic voltammetry study has shown that the co-support ceria contributes to the remarkable decrease of the onset oxidation potential of ethanol. It is proposed that ceria promotes the formation at low potentials of species adsorbed on Pd, Pd(I)-OH(ads), that are responsible for ethanol oxidation.

A Biologically Inspired Organometallic Fuel Cell (OMFC) That Converts Renewable Alcohols into Energy and Chemicals

The simultaneous conversion of alcohols and sugars into energy and chemicals is a target of primary importance in sustainable chemistry. The realization of such a process provides renewable energy with no CO2 emission and, at the same time, leads to the production of industrially relevant feedstocks, such as aldehydes, ketones, and carboxylic acids, from biomasses. Two established types of fuel cells operating in alkaline media can convert the free energy of alcohols (RCH2OH) into electrical energy and the corresponding carboxylate product: the direct alcohol fuel cell (DAFC), and the enzymatic biofuel cell (EBFC). 8] In a DAFC, an alcohol such as ethanol (CH3CH2OH) is selectively converted into acetate (CH3COO ) and the electrolyte is an anionexchange membrane. On the anode, ethanol is oxidized, releasing four electrons [Eq. (1)] that are utilized to reduce one oxygen molecule to four hydroxide ions on the cathode [Eq. (2)]. Efficient devices of this type have been recently developed for a variety of renewable alcohols and polyalcohols, such as ethylene glycol, glycerol, 1,2-propandiol, and C6 and C5 sugars. [3–6] (For drawings of a DAFC, a EBFC, and typical power density curves, see the Supporting Information, Figure S1 a–d).

Electrochemical milling and faceting: Size reduction and catalytic activation of palladium nanoparticles

Improved performance through milling: A method for enhancing the catalytic activity of supported metal nanoparticles is reported. This method enhances the activity for the ethanol electro-oxidation of a supported palladium catalyst. The much higher catalytic performance is ascribed to the increased electrochemically active surface area as well as the generation of high-index facets at the milled nanoparticle surface.

Confining Phosphanes Derived from Cyclodextrins for Efficient Regio- and Enantioselective Hydroformylation**

Two confining phosphane ligands derived from either α- or β-cyclodextrin produce singly P(III) -ligated metal complexes with unusual coordination spheres. High-pressure NMR studies have revealed that rhodium hydride complexes of the same type are also formed under hydroformylation conditions. This unique feature strongly favors the formation of the branched aldehyde at the expense of the linear one with high enantioselectivity in the rhodium-catalyzed hydroformylation of styrene.

Isomerization of allylic alcohols to carbonyl compounds by aqueous-biphase rhodium catalysis

Isomerization of allylic and homoallylic alcohols is catalyzed by the zwitterionic Rh(I) complex (sulphos)Rh(cod) in water–n-octane to give the corresponding aldehyde or ketone in high yields and chemoselectivity. A π-allyl metal hydride mechanism is proposed on the basis of various independent experiments in both homogeneous and biphasic systems [sulphos=−O3S(C6H4)CH2C(CH2PPh2)3].

Synthesis, platinum(II) complexes and structural aspects of the new tetradentate phosphine cis,trans,cis-1,2,3,4-tetrakis(diphenylphosphino)cyclobutane

Abstract Several novel dimers of the composition [M 2 Cl 4 ( trans -dppen) 2 ] (M=Ni ( 1 ), Pd ( 2 ), Pt ( 3 )) containing trans -1,2-bis(diphenylphosphino)ethene ( trans -dppen) have been prepared and characterized by X-ray diffraction methods, NMR spectroscopy ( 195 Pt{ 1 H}, 31 P{ 1 H}), elemental analyses, and melting points. The intramolecular [2+2] photocycloaddition of the two diphosphine-bridges in 3 produces [Pt 2 Cl 4 (dppcb)] ( 4 ), where dppcb is the new tetradentate phosphine cis,trans,cis -1,2,3,4-tetrakis(diphenylphosphino)cyclobutane. Neither 1 nor the free diphosphine trans -dppen shows this reaction. In the case of 2 the photocycloaddition is slower than in 3 . This difference can be explained by the shorter distance between the two aliphatic double bonds in 3 than in 2 , but also different transition probabilities within ground and excited states of the used metals could be involved. Furthermore, variable-temperature 31 P{ 1 H} NMR spectroscopy of 2 or 3 reveals a negative activation entropy of 2 for the [2+2] photocycloaddition, but a positive of 3 . The removal of chloride from 4 by precipitating AgCl with AgBF 4 , and subsequent treatment with 2,2′-bipyridine (bipy) or 1,10-phenanthroline (phen) leads to [Pt 2 (dppcb)(bipy) 2 ](BF 4 ) 4 ( 5 ) and [Pt 2 (dppcb)(phen) 2 ](BF 4 ) 4 ( 6 ), respectively. In an analogous reaction of 4 with PMe 2 Ph or PMePh 2 , [Pt 2 (dppcb)(PMe 2 Ph) 4 ](BF 4 ) 4 ( 7 ) and [Pt 2 (dppcb)(PMePh 2 ) 4 ](BF 4 ) 4 ( 8 ) are formed. Complexes 1 – 8 show square–planar coordinations, where the compounds 4 – 8 have also been characterized by the above mentioned methods together with fast atom bombardment mass spectrometry ( 7 , 8 ). The crystal structure of 4 reveals two conformations, which arise from an energetic competition between the sterical demands of dppcb and an ideal square–planar environment of Pt(II). The free tetraphosphine dppcb can be obtained easily from 4 by treatment with NaCN. It has been characterized fully by the above methods including 13 C{ 1 H} and 1 H NMR spectroscopy. The X-ray structure analysis shows the pure MMMP-enantiomer in the solid crystal, which is therefore optically active. This chirality is induced by a conformation of dppcb, where all four PPh 2 groups are non-equivalent. Variable-temperature 31 P{ 1 H} NMR spectroscopy of dppcb confirms this explanation, since the single signal at room temperature is split into two doublets at 183 K. The goal of this article is to demonstrate the facile production of a new tetradentate phosphine from a diphosphine precursor via Pt(II) used as a template.

Bis-alkoxycarbonylation of styrene by pyridinimine palladium catalysts

Pyridinimine-modified Pd(II) complexes of general formulae (N-N′)Pd(Y)2 catalyze the methoxycarbonylation of styrene to give dimethyl phenylsuccinate as the largely major product [N-N′ = py-2-C(R)N(2,6-R′C6H3), R = H, Me; R′ = Me, i-Pr; 6-Mepy-2-C(H)N[2,6-(i-Pr)2C6H3]; py-2-C(H)N(C6H5); Y = acetate, trifluoroacetate]. The influence of various catalytic parameters on the overall conversion of styrene to carbonylated products and on the product selectivity has been studied by systematically varying the type of palladium initiator, the concentrations of organic oxidant (1,4-benzoquinone) and protic acid (p-toluenesulfonic acid), and the CO pressure. By an appropriate choice of the structure of the pyridinimine ligand and of the reaction parameters, turn-over numbers as high as 96 and selectivities in dimethyl phenylsuccinate as high as 98% were obtained. In particular, the overall conversion of styrene is controlled by the steric properties of the alkyl substituents on the imine aryl group, while the nature of the substituent (H or Me) on the imine carbon influences the selectivity. The addition of 2 equivalents of TsOH to the catalytic mixtures generally increased the styrene conversion but lowered the selectivity in dimethyl phenylsuccinate due to greater production of methyl 3,6-diphenyl-4-oxohexanoate. Further additions of TsOH (up to 6 equivalents) resulted in better selectivities and lower conversions for all precursors.