TY - JOUR A1 - Grohmann, I. A1 - Kemnitz, E. A1 - Lippitz, Andreas A1 - Unger, Wolfgang T1 - Curve Fitting of Cr2p Photoelectron Spectra of Cr2O3 and CrF3 JF - Surface and interface analysis KW - Photoelektronenspektroskopie KW - Kurvenglättung KW - Chrom PY - 1995 SN - 0142-2421 SN - 1096-9918 VL - 23 SP - 887 EP - 891 PB - Wiley CY - Chichester AN - OPUS4-678 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Mehner, Hartmut A1 - Witke, Klaus A1 - Feist, M. A1 - Troyanov, S.I. A1 - Kemnitz, E. T1 - Halogenometallate von Übergangselementen mit Kationen stickstoffhaltiger heterozyklischer Basen. VII Zwei Oxidationsstufen und vier verschiedene Koordinationen von Eisen in einer Verbindung. Synthese, Kristallstruktur und spektroskopische Charakterisierung von 1,4-Dimethylpiperazinium-Chloroferrat(II, III), (dmpipzH2)6[FeIICl4]2[FeIIICl4]2[FeIICl5] [FeIIICl6] JF - Zeitschrift für anorganische und allgemeine Chemie = Journal of inorganic and general chemistry KW - Halogenometallate KW - Spektroskopische Charakterisierung PY - 1999 SN - 0044-2313 SN - 1521-3749 SN - 0372-7874 SN - 0863-1786 SN - 0863-1778 N1 - Sprachen: Deutsch/Englisch - Languages: German/English VL - 625 IS - 1 SP - 141 EP - 146 PB - Wiley-VCH CY - Weinheim AN - OPUS4-738 LA - mul AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Feist, M. A1 - Troyanov, S.I. A1 - Mehner, Hartmut A1 - Witke, Klaus A1 - Kemnitz, E. T1 - Zwei Oxidationsstufen und vier verschiedene Koordinationen von Eisen in einer Verbindung. Synthese, Kristallstruktur und spektroskopische Charakterisierung von 1,4-Dimethylpiperazinium-Chloroferrat(II, III), (dmpipzH2)6[FeIICl4]2[FeIIICl4]2[FeIICl5] [FeIIICl6] JF - Zeitschrift für anorganische und allgemeine Chemie = Journal of inorganic and general chemistry KW - 1,4-Dimethylpiperazinium chloroferrate(II,III) KW - Crystal Structure KW - Trigonal-bipyramidal pentachloroferrate(II) KW - Mössbauer, Raman spectroscopy PY - 1999 SN - 0044-2313 SN - 1521-3749 SN - 0372-7874 SN - 0863-1786 SN - 0863-1778 IS - 625 SP - 141 EP - 146 PB - Wiley-VCH CY - Weinheim AN - OPUS4-2305 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Witke, Klaus A1 - Kunze, Ralf A1 - Neubert, Dietmar A1 - Mehner, Hartmut A1 - Feist, M. A1 - Kemnitz, E. T1 - Two oxidation states and four different coordinations of iron in an unusual chloro complex: TG-MS, Raman and Mössbauer spectroscopic investigations of the thermal behaviour JF - Thermochimica Acta N2 - Conventional simultaneous thermal analysis, capillary-coupled TG–MS, in situ and ex situ Raman and Mössbauer spectroscopy, as well as chemical analysis have been used for the investigation of the first decomposition step of the mixed valence chloroferrate (dmpipzH2)6[Fe(II)Cl4]2[Fe(III)Cl4]2[Fe(II)Cl5][Fe(III)Cl6]. Under argon at ca. 200°C, an almost complete reduction proceeds in a solid state reaction forming Fe(II). It is accompanied by the release of HCl and, to a minor degree, carbon containing species. A multi-phase product with at least two chloroferrate species, coke, and C,H,N-containing polymers is formed. Binuclear iron complexes, such as (dmpipzH)2[Fe(II)2Cl6], and small amounts of (dmpipzH)[Fe(III)Cl4] have been proposed to be the major and minor component of the product mixture, respectively. KW - Mixed valence chloroferrate KW - Thermal decomposition KW - Intramolecular reduction PY - 2000 DO - https://doi.org/10.1016/S0040-6031(00)00546-3 SN - 0040-6031 SN - 1872-762X VL - 361 IS - 1-2 SP - 53 EP - 60 PB - Elsevier CY - Amsterdam AN - OPUS4-988 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Lippitz, Andreas A1 - Unger, Wolfgang A1 - Boese, O. A1 - Kemnitz, E. T1 - y-Al2O3 by Au 4f7/2-referenced XPS and XAES JF - Surface science spectra N2 - Powder x-ray diffraction (XRD) defined -Al2O3 has been investigated by x-ray photoelectron spectroscopy (XPS) and x-ray excited Auger electron spectroscopy (XAES). The Au 4f7/2 orbital is used for static charge referencing. This feature originates from well-defined and chemically inert 20 nm highly dispersed gold particles deposited on the sample surface. The particles, with a narrow particle size distribution, were obtained from a highly purified colloidal solution (sodium concentration below 1 mg/l). This procedure allows a determination of gold-referenced XPS and XAES data sets. ©2001 American Vacuum Society. KW - Au 4f referenced XPS data KW - Aluminium KW - Oxide PY - 2001 UR - http://scitation.aip.org/vsearch/servlet/VerityServlet?KEY=SSSPEN&ONLINE=YES&smode=strresults&sort=chron&maxdisp=25&threshold=0&possible1zone=article&possible4=lippitz&possible4zone=author&bool4=and&fromyear=2001&OUTLOG=NO&viewabs=SSSPEN&key=DISPLAY&docID DO - https://doi.org/10.1116/11.20020305 SN - 1055-5269 SN - 1520-8575 VL - 8 IS - 1-4 SP - 214 EP - 219 PB - AIP CY - Woodbury, NY AN - OPUS4-1910 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Mehner, Hartmut A1 - Feist, M. A1 - Stößer, R. A1 - Scholz, G. A1 - Kemnitz, E. A1 - Dwelk, H. T1 - Halogeno metallates of transition elements with cations of nitrogen-containing heterocyclic bases, IX. Moessbauer and ESR spectroscopic investigation of aquachloro- and bromoferrates(III). On the compatibility of structural information obtained by spectroscopic and diffraction methods JF - Solid state sciences N2 - The 57Fe-Moessbauer spectrum of (dmpipzH2)2[FeIII(H2O)2Cl4][FeIII Cl4]Cl2 (1) consists of two doublets caused by a strongly distorted octahedral and a non-distorted tetrahedral component. Both (dmpipzH2)[FeIIIBr4]2 (2) and (trienH2)[FeIIIBr4]Br (3) show only one doublet indicating a more strongly distorted iron(III) species for 2 and a less-distorted one in the case of 3. For all compounds investigated, the ESR spectra reveal the existence of ground states with predominant antiferromagnetic coupling. The Néel temperatures amount to <4.2 K for 1, 4 K for 3 and 48 K for 2. In the case of 2, both the Moessbauer and the ESR spectra reveal the formation of exchange-coupled {FeBr4} units which has been attributed to a significant cation influence. The fine structure of residual paramagnetic [FeBr4]- subunits remaining in the crystalline matrix could be directly determined. Temperature dependent AC and DC susceptibility measurements of 2 and 3 confirmed the results. KW - Iron coordination KW - Antiferromagnetic coupling KW - Exchange-coupled units KW - ESR fine structure KW - Magnetic susceptibility PY - 2002 DO - https://doi.org/10.1016/S1293-2558(01)01193-1 SN - 1293-2558 SN - 1873-3085 VL - 4 IS - 1 SP - 109 EP - 115 PB - Elsevier CY - Amsterdam AN - OPUS4-1311 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Kemnitz, E. A1 - Zhu, Y. A1 - Adamczyk, Burkart T1 - Enhanced Lewis acidity by aliovalent cation doping in metal fluorides JF - Journal of fluorine chemistry N2 - A model regarding the generation of acidity in binary metal fluorides has been proposed and its validity has been examined for several binary fluoride systems with the general compositions MF3/M'F3 and MF2/M'F3. In accordance with this hypothesis, the binary systems (CrF3/AlF3, CrF3/FeF3 and AlF3/VF3) do not show acidities larger than the sum of the acidities of the component fluorides. The hypothesis predicts the generation of Lewis acidity when MF2 is the major component (host) and generation of Brønsted acidity when MF3 acts as the host for the MF2/M'F3. The experimental results (surface acidity and catalytic activity) confirmed the predictions made from this hypothesis for binary combinations MgF2/ M'F3 (M'=Cr, Al, Fe, V). The application of this model is discussed in terms of other parameters: ionic radii and the fluoride affinity of the metal fluorides involved. PY - 2002 DO - https://doi.org/10.1016/S0022-1139(02)00022-2 SN - 0022-1139 SN - 1873-3328 VL - 114 SP - 163 EP - 170 PB - Elsevier CY - Amsterdam AN - OPUS4-1661 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Böse, Olaf A1 - Unger, Wolfgang A1 - Kemnitz, E. A1 - Schroeder, S. L. M. T1 - Active sites on an oxide catalyst for F/Cl-exchange reactions: X-ray spectroscopy of fluorinated y-Al2O3 JF - Physical chemistry, chemical physics N2 - The dismutation of CHClF2 to CHF3 and CHCl3 was used to probe the effect of γ-Al2O3 fluorination on fluorine-against-chlorine (Cl/F) exchange reactions. X-ray photoelectron spectroscopy (XPS), X-ray excited Auger electron spectroscopy (XAES) and X-ray absorption near edge structure (XANES) spectroscopy were employed to probe the modifications at the surface of γ-Al2O3 accompanying the initial stages of fluorination. The results suggest that fluorine uptake by γ-Al2O3 starts initially at the surface of the oxide particles, with the formation of a fluorine species that is characterised by a single bond and a high effective charge q. Catalytic Cl/F-exchange is only observed after accumulation of higher fluorine concentrations, for which insertion of fluorine into the sub-surface region of the oxide crystallites has commenced. Quantitative XPS shows that the fluorination level must exceed approximately 10 atom% of the anions to achieve catalytic activity. The spectroscopic evidence suggests that the formation of aluminium oxofluorides is sufficient to provide catalytic activity. The presence of an AlF3 phase is not a condition for the observation of catalytic activity, even though defect-rich AlF3 is ultimately the endpoint of the fluorination process and is itself a Cl/F exchange catalyst. PY - 2002 DO - https://doi.org/10.1039/b110792e SN - 1463-9076 SN - 1463-9084 VL - 4 IS - 12 SP - 2824 EP - 2832 PB - The Royal Soc. of Chemistry CY - Cambridge AN - OPUS4-6940 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Ünveren, Ercan A1 - Kemnitz, E. A1 - Hutton, S. A1 - Lippitz, Andreas A1 - Unger, Wolfgang T1 - Analysis of highly resolved x-ray photoelectron Cr 2p spectra obtained with a Cr2O3 powder sample prepared with adhesive tape JF - Surface and interface analysis KW - High-resolution XPS KW - Cr2O3 powder KW - Multiplet splitting PY - 2004 SN - 0142-2421 SN - 1096-9918 VL - 36 SP - 92 EP - 95 PB - Wiley CY - Chichester AN - OPUS4-3427 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Scheurell, K. A1 - Hoppe, E. A1 - Brzezinka, Klaus-Werner A1 - Kemnitz, E. T1 - Bulk and surface properties of highly dispersed VOx/ZrO2, VOx/SiO2 and VOx/TiO2/SiO2 systems and their relevance for propane oxidation JF - Journal of materials chemistry N2 - Highly dispersed vanadium-doped metal oxides such as VOx/ZrO2, VOx/SiO2 and VOx/TiO2/SiO2 with vanadium contents between 0 and 25 mole% were prepared by special bulk preparation methods (coprecipitation and sol–gel, followed by freeze-drying). Bulk and surface properties of the obtained mixed oxide solid solutions were thoroughly investigated by different analytical methods (Raman and FTIR spectroscopy, TPD, H2-TPR, oxygen isotope measurements etc.). Moreover, the catalytic behaviour of the oxides was studied for the example of the oxidative dehydrogenation (ODH) of propane to propylene. Independent of the preparation method, the catalytic behaviour of vanadium-doped ZrO2 and TiO2 phases is very similar. Both metal oxide solid solutions are very active in propane ODH whereas the catalytic activity of VOx/SiO2 is relatively low. On the other hand, the reduction of the catalytic activity is accompanied by an improved selectivity for the formation of propylene. The correlation between the catalytic activity and the acidity of the oxide systems is discussed. Oxidation experiments with 18O2 clearly show that the ODH reaction occurs according to the Mars–van Krevelen mechanism. KW - Vanadium-doped metal oxides KW - Solid solutions KW - Coprecipation KW - Sol-gel-method KW - Propan oxidation KW - Catalytic activity KW - Oxygen mobility PY - 2004 DO - https://doi.org/10.1039/b402924k SN - 0959-9428 SN - 1364-5501 VL - 14 IS - 16 SP - 2560 EP - 2568 PB - Royal Society of Chemistry CY - Cambridge AN - OPUS4-4152 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -