Rolf W. Berg

Catalytic Performance of Zeolite-Supported Vanadia in the Aerobic Oxidation of 5-hydroxymethylfurfural to 2,5-diformylfuran

The catalytic performance of zeolite‐supported vanadia catalysts was examined for the aerobic oxidation of 5‐hydroxymethylfurfural (HMF) to 2,5‐diformylfuran (DFF) in organic solvents such as N,N‐dimethylformamide (DMF), methyl isobutyl ketone, toluene, trifluorotoluene and DMSO. Catalysts based on the four different zeolite supports H‐beta, H‐Y, H‐mordenite, and H‐ZSM‐5 with 1–10 wt % vanadia loading were prepared and characterized by nitrogen physisorption, X‐ray powder diffraction, scanning electron microscopy, ammonia temperature‐programmed desorption, Raman spectroscopy and UV/Vis spectrophotometry. The H‐beta zeolite catalysts were found to contain highly dispersed vanadium oxide species at all loadings, and provided the highest reaction selectivity towards DFF and the lowest metal leaching of the examined systems. In particular, 1 wt % V2O5/H‐beta was found to be a stable, recyclable, and non‐leaching catalyst for the production of DFF under mild conditions in DMF as solvent, although with low DFF yield. To increase the yield, oxidation of HMF at elevated pressures was also investigated with this catalyst. Under optimized conditions, a reaction selectivity towards DFF of >99 % at 84 % HMF conversion was obtained, albeit with some contribution from lixiviated species to the total catalyst activity.

Molten triazolium chloride systems as new aluminum battery electrolytes

The possibility of using molten mixtures of 1,4-dimethyl-1,2,4-triazolium chloride (DMTC) and aluminum chloride (AlCl[sub 3]) as secondary battery electrolytes was studied, in some cases extended by the copresence of sodium chloride. DMTC-AlCl[sub 3] mixtures demonstrated high specific conductivity in a wide temperature range. The equimolar system is most conductive and has [kappa] values between 4.02 [times] 10[sup [minus]5] and 7.78 [times] 10[sup [minus]2]S cm[sup [minus]1] in the range from [minus]31 to 123 C, respectively. The electrochemical window of DMTC-containing sodium tetrachloroaluminate melts varied in the region of 2.5 to 2.2 V (150--170 C) depending on melt acidity and anode material. DMTC, being specifically adsorbed and reduced on the tungsten electrode surface, had an inhibiting effect on the aluminum reduction, but this effect was suppressed on the aluminum substrate. An electrochemical process with high current density (tens of milliamperes per square centimeter) was observed at 0.344V on the acidic sodium tetrachloroaluminate background, involving a free triazolium radical mechanism. Molten DMTC-AlCl[sub 3] electrolytes are acceptable for battery performance and both the aluminum anode and the triazolium electrolyte can be used as active materials in the acidic DMTC-AlCl[sub 3] mixtures.

Morphological Changes at the Interface of the Nickel‐Yttria Stabilized Zirconia Point Electrode

The H 2 -H 2 O, Ni/YSZ point electrode has been investigated using long-term potential step measurements and impedance spectroscopy at 1273 K. Morphological and structural changes at the electrode interface were evaluated by electron microscopy, energy dispersive X-ray analysis, and Raman spectroscopy ex situ. The anodic current was found to induce a self-catalytic effect on the electrode, an the anodic steady state current increased to more than twice the initial value with a time constant of about 40 h. In contrast, cathodic polarization reduced the performance of the electrode, and the cathodic current decreased significantly with a time constant of about 20 h. Redistribution of material in the reaction zone is suggested to control most of the changes in electrode activity. At anodic overpotentials it was observed that Ni was transported to the electrolyte surface, forming a necklace of Ni particles around the electrode/electrolyte contact. This is believed to increase the three-phase boundary (TPB) length and account for the higher activity of the electrode. At cathodic overpotentials the transfer of Ni to the YSZ was found to be restricted, and it is proposed that agglomeration of dispersed metal particles reduced the TPB length, and accordingly the cathodic current. In addition to the morphological modifications, the catalytic properties of the surfaces were significantly altered as the electrode was polarized. Transformation from cubic to tetragonal YSZ, due to segregation of the material, was observed on the surface of the electrolyte when the sample was kept at working conditions for long periods of time (135 days). The passage of current was not found to generate any permanent phase transformation in the YSZ.

Low temperature vibrational spectroscopy. I. Hexachlorotellurates

Far infrared and Raman spectra of six hexachlorotellurate (IV) salts have been obtained at ∼100 K for the first time. In the rubidium, cesium, ammonium, and tetramethylammonium salts the Raman active T2g cation lattice translatory mode was found. In the monoclinic K2[TeCl6] a number of low frequency lattice modes were observed and interpreted in terms of a phase transition near 165 K, similar to transitions in other K2[MX6] salts. The cubic tetramethylammonium hexachlorotellurate salt undergoes a phase transition of supposed first order at a temperature near 110 K, corresponding to transitions known in analogous uranium and tin compounds. Possible reasons for the transitions are discussed. In the low temperature phases the ν4 and ν6 bendings of [TeCl6]2− have been identified with bands near ∼130 and ∼110 cm−1. No evidence seemed to favor any stereochemical distortion due to the lone pair of electrons present in hexachlorotellurates.

Vibrational spectroscopy on protons and deuterons in proton conducting perovskites

A short review of IR-spectroscopy on protons in perovskite structure oxides is given. The nature of possible proton sites, libration and combination tones and degree of hydrogen bonding is emphasised. Three new spectroscopic experiments and/or interpretations are presented. An IR-microscopy experiment was performed on the protonic conductor Ba3(Ca 1+ xNb2 � x)O9 � d, x=0.18. The H/D concentration profile of a cross-section of the sample after partial isotopic exchange can be visualised; proton containing La0.9Ca0.1ErO3 was studied up to 200 jC by Raman spectroscopy. At 200 jC, the OH-stretch cannot be observed due to thermal broadening, but the peak reappears upon cooling; the OH and OD absorption bands in BaCe1 � xNdxO3 are very broad and, in addition, an electronic transition of Nd +3 is observed at 1900–1930 cm � 1 ; finally, IR reflectance spectroscopy on BaZr0.9Y0.1O3 ,L a0.8Sr0.2ScO3 ,L a0.9Sr0.1Sc0.9Mg0.1O3 and SrCe0.95Y0.05O3 shows at least three types of proton positions. D 2002 Published by Elsevier Science B.V.

High-Pressure Measuring Cell for Raman Spectroscopic Studies of Natural Gas

A system for obtaining Raman spectra of gases at high pressure has been constructed. In order to ensure that a natural gas sample is totally representative, a high-pressure gas-measuring cell has been developed, built up by stainless steel fittings and a sapphire tube. The design and construction of this cell are described. A perfect pressure seal has been demonstrated up to 15.0 MPaA (MPa absolute). The cell has been successfully used to obtain Raman spectra of natural gas samples. Some of these spectra are presented and assigned. The most remarkable observation in the spectra is that it is possible to detect hydrogen sulfide at concentrations of 1–3 mg H2S/Nm3. An attempt to make a quantitative analysis of natural gas by the so-called “ratio method” is presented. In addition to this, the relative normalized differential Raman scattering cross sections for ethane and i-butane molecules at 8.0 MPaA and 10.2 MPaA have been determined.

Electrolyte Additives for Phosphoric Acid Fuel Cells

Electrochemical characteristics of a series of modified phosphoric acid electrolytes containing fluorinated carbon compounds and silicone fluids as additives are presented. When used in phosphoric acid fuel cells, the modified electrolytes improve the performance due to the enhanced oxygen reduction rate. Among useful additives the authors found potassium perfluorohexanesulfonate (C[sub 6]F[sub 13]SO[sub 3]K), potassium nonafluorobutanesulfonate (C[sub 4]F[sub 9]SO[sub 3]K), perfluorotributylamine [(C[sub 4]F[sub 9])[sub 3]N], and polymethylsiloxanes [(-Si(CH[sub 3])[sub 2]O-)n]. The wettability of the electrodes by the modified electrolytes also is discussed, as if fuel-cell performance with the modified electrolytes. Specific conductivity measurements of some of the modified phosphoric acid electrolytes are reported. At a given temperature, the conductivity of the C[sub 4]F[sub 9]SO[sub 3]K-modified electrolyte decreases with an increasing amount of the additive; the conductivity of the (C[sub 4]F[sub 9])[sub 3]N-modified electrolyte, remains at the same value as the conductivity of the pure phosphoric acid. At a given composition, the conductivity of any modified electrolyte increases with temperature. The authors conclude that the improved cell performance for modified electrolytes is not due to any increase in conductivity.

Low temperature vibrational spectroscopy. II. Evidence for order–disorder phase transitions due to weak C–H⋅⋅⋅Cl hydrogen bonding in tetramethylammonium hexachloroplatinate (IV), ‐tellurate (IV), and ‐stannate (IV) and the related perdeuterated compounds

The low frequency infrared and Raman spectra of normal and per‐deuterated ((CH3)4N)2[MCl6] (M=Pt, Te, or Sn) have been measured at temperatures down to ∼100 K and evidence for phase transitions was found. The spectra have been carefully assigned and it was shown that bands due to forbidden methyl torsions and other noncubic features play a role, especially in spectra at low temperatures. Possible site symmetries of the [PtCl6]2− ion, which cannot have strictly Oh symmetry in either phase, have been deduced. The spectra of a mixed Pt : Te compound showed that the hexachlorometallate anions vibrate approximately independent of each other. The results have been compared with von der Ohe’s recent extensive low temperature Raman study on protonated compounds with M=U, Sn, and Zr, and his conclusions are discussed. It is shown that crystals of this kind can be characterized by methyl–chlorine interaction and it is suggested that the phase transitions are caused by an ordering of rotationally disordered methyl g...

The vibrational spectrum of the normal and perdeuterated tetramethylammonium ion

Abstract Rather complete Raman and i.r. spectra of the two isotopic ions in aqueous solutions have been obtained and qualitatively interpreted. Some revisions of previous assignments are suggested, based on the new data and the isotopic frequency shifts. The presence of complex Fermi resonances was found in the CD stretching range.

Infrared and far infrared spectra of dihalo(ethylenediamine) palladium(II) and platinum(II)

Abstract Infrared and far i.r. room temperature spectra of solid square planar mono(ethylenediamine) halide complexes of Pd and Pt are obtained. Group vibrations are assigned with the use of two C-deuterated compounds. A comparison of factor group and site group analyses shows that the former is necessary to explain the finer details of the spectra. Crystal data of [PdenCl2] and [PtenI2] are reported.