Klaus Stöwe

High-throughput screening of nanoparticle catalysts made by flame spray pyrolysis as hydrocarbon/NO oxidation catalysts.

We describe here the use of liquid-feed flame spray pyrolysis (LF-FSP) to produce high surface area, nonporous, mixed-metal oxide nanopowders that were subsequently subjected to high-throughput screening to assess a set of materials for deNO(x) catalysis and hydrocarbon combustion. We were able to easily screen some 40 LF-FSP produced materials. LF-FSP produces nanopowders that very often consist of kinetic rather than thermodynamic phases. Such materials are difficult to access or are completely inaccessible via traditional catalyst preparation methods. Indeed, our studies identified a set of Ce(1-x)Zr(x)O(2) and Al(2)O(3)-Ce(1-x)Zr(x)O(2) nanopowders that offer surprisingly good activities for both NO(x) reduction and propane/propene oxidation both in high-throughput screening and in continuous flow catalytic studies. All of these catalysts offer activities comparable to traditional Pt/Al(2)O(3) catalysts but without Pt. Thus, although Pt-free, they are quite active for several extremely important emission control reactions, especially considering that these are only first generation materials. Indeed, efforts to dope the active catalysts with Pt actually led to lower catalytic activities. Thus the potential exists to completely change the materials used in emission control devices, especially for high-temperature reactions as these materials have already been exposed to 1500 degrees C; however, much research must be done before this potential is verified.

Fluorescence-based high throughput screening for noble metal-free and platinum-poor anode catalysts for the direct methanol fuel cell.

We describe here the results of a high throughput screening study for direct methanol fuel cell (DMFC) anode catalysts consisting of new elemental combinations with an optical high-throughput screening method, which allows the quantitative evaluation of the electrochemical activity of catalysts. The method is based on the fluorescence of protonated quinine generated during electrooxidation of methanol. The high-throughput screening included noble-metal free binary and ternary mixed oxides of the elements Al, Co, Cr, Cu, Fe, Mn, Mo, Nb, Ni, Ta, Ti, Zn, and Zr in the oxidized form as well as after prior reduction in hydrogen. In addition 318 ternary and quaternary Pt-containing materials composed out of the mixed oxides of Bi, Ce, Co, Cr, Cu, Fe, Ga, Ge, In, La, Mn, Mo, Nb, Nd, Ni, Pr, Sb, Sn, Ta, Te, Ti, V, Zn, and Zr with a molar Pt-ratio of 10% and 30% were screened. Validation and long time experiments of the hits were performed by cyclovoltammetry (CV). The microstructural stability of the electrode preparations of the lead compositions was studied by X-ray diffraction (XRD) pattern analysis.

Crystal structure and magnetic properties of CeTe2

Abstract X-ray diffraction single-crystal structure analysis of CeTe2 prepared by chemical vapor transport reactions in the presence of mg-traces of iodine revealed superstructure reflections indicating a (2×2×2) supercell of the basic anti-Fe2As type in contrast to the (2×2×1) supercell found for LaTe2. The best interpretation of data set was obtained choosing for CeTe2 the tetragonal space group P4 with the lattice parameters a=899.75(5) pm and c=1821.2(1) pm (Z=16). The doubling of the c axis compared to LaTe2 is observed due to different polyanionic structural motifs in the heights z≈0 and z≈ 1 2 . These are a herringbone pattern of [Te2] dumbbell pairs — a topology which is also found in LaTe2 — isolated [Te4] four-membered rings in z≈ 1 2 and additionally [Te8] branched four-membered rings in z≈ 1 2 . These structural elements give a diffraction pattern, which is all in all to be explained by a statistical superposition of the different elements. Magnetic susceptibility measurements revealed pronounced crystal field effects for the trivalent Ce ions, but apart from that are in agreement with former investigations finding a magnetic transition below T=4 K due to ferrimagnetic ordering. A formerly observed spin sequence of the magnetic moments at different sites A and B of ABBA,A may now be well understood by a classification of the Ce ions into two types with different coordinational environment in the actual structure model.

DIE SYNTHESE UND KRISTALLSTRUKTUR VON K2UTE3

Die Synthese von K2UTe3 gelang uber Schmelzflusreaktionen ausgehend von K2Te3 und Uranmetall im Molverhaltnis 2 : 1 bei 600 bis 800 °C. Gut ausgebildete Kristalle wurden durch Auswaschen der Schmelzreguli mit flussigem NH3 isoliert. Pulverproben von K2UTe3 sind auch bei stochiometrischem Ansatz aus K2Te3 und Uran in reiner Form zuganglich. Das Edukt K2Te3 wurde in flussigem Ammoniak aus den Elementen mit einer speziell fur die Synthese von Alkalimetallchalkogeniden entwickelten Apparatur erhalten. Die Rontgenstrukturanalyse an Einkristallen ergab fur K2UTe3 die monokline Raumgruppe C2/m (Z = 4) und die Gitterparameter a = 800,41(3) pm, b = 1387,67(5) pm, c = 851,63(4) pm und β = 108,495(3)°. Die Kristallstruktur der Verbindung kann als Auffullungsvariante des AlCl3-Strukturtyps betrachtet werden. Die Existenz der zu K2UTe3 isotyp kristallisierenden Verbindung Rb2UTe3 wurde durch rontgenographische Pulveruntersuchungen nachgewiesen. The Synthesis and Crystal Structure of K2UTe3 Syntheses of K2UTe3 were performed via polytelluride fluxes from K2Te3 and metallic uranium in the molar ratio 2 : 1 at 600 to 800 °C. Well-formed crystals were isolated by washing the reguli with liquid ammonia. One-phase powder samples of K2UTe3 are also available by reactions of stoichiometric mixtures of K2Te3 and uranium. K2Te3 was prepared in liquid ammonia from the elements using a glass apparatus specially designed for the synthesis of alkali metal chalcogenides. By x-ray structure analyses of single crystals we found K2UTe3 to crystallize monoclinic (space group C2/m, Z = 4) with the lattice parameters a = 800.41(3) pm, b = 1387.67(5) pm, c = 851.63(4) pm and β = 108.495(3)°. The crystal structure of the compound may be regarded as a stuffed AlCl3-type structure. The existence of an analogous compound Rb2UTe3 crystallizing isotypically to K2UTe3 has been shown by x-ray powder investigations.

Niobium: Activator and Stabilizer for a Copper-Based Deacon Catalyst

A highly active Cu‐based Deacon catalyst with an enhanced lifetime was developed by combining two corrosion‐resistant high‐throughput reactor setups in this combinatorial study. Catalyst activities were studied in a sequential 10‐fold reactor equipped with online MS. For accelerated catalyst ageing studies, a parallel 10‐fold reactor was used. The starting point was a CuTi mixed‐metal oxide found in former discovery investigations. As development criteria, catalyst stability and HCl conversion were selected. The amount of Cu in the CuTi catalysts were analyzed before and after the ageing process by X‐ray fluorescence spectroscopy. Dopant elements were selected that are reported to form oxides with a high corrosion resistance against gaseous HCl. Our study revealed that doping with 1 mol % Nb reduced the Cu leaching during the reaction. Furthermore, the activation energy was decreased by Nb, which enhanced the chlorine production.

Optical High-Throughput Screening for Activity and Electrochemical Stability of Oxygen Reducing Electrode Catalysts for Fuel Cell Applications

A fluorescence-based electro-optical high-throughput method and setup for testing the oxygen reduction reaction (ORR) activity and electrochemical stability of 60 materials in parallel is described. We present thus a quantitative method for activity measurements for ORR-catalysts by optical fluorescence data acquisition. The fluorescence behavior of fluorescein, phloxine B, and umbelliferone as indicators is presented. The effect of oxygen concentration, saturation, and supply on electrochemical response is presented. Corrections for internal resistance differences and intensity differences are described. The final method allowed position independent determination of activities on the working-electrode library, containing up to 60 different electrocatalysts. A total of 378 selected mixed oxides have been studied. Cu/Ni/Mn and Co/Ni/Mn oxides proved electrochemically most active and comparable to a Pt-containing reference catalyst.

Synthesis and Mechanical Properties of Organic–Inorganic Hybrid Materials from Lignin and Polysiloxanes

The preparation of silica-containing organic-inorganic hybrid materials composed of kraft lignin, alkoxysilanes, and organic linkers was investigated. 3-Glycidyloxypropyltrimethoxysilane, 3-(triethoxysilyl)propylisocyanate (IPTES), and bis(trimethoxysilyl)hexane were selected as the most promising linkers. The best materials obtained showed improved mechanical and thermal properties compared with lignin itself. The reaction of the hydroxyl groups with IPTES and the sol-gel reaction between the organic linker molecules were studied by attenuated total reflectance FTIR and solid-state ²⁹Si magic-angle spinning NMR spectroscopy. The homogeneous composition was demonstrated by electron microscopy and energy-dispersive X-ray spectroscopy mapping. The mechanical properties were investigated by microindentation and dynamic mechanical thermal analysis.

Zur Neuuntersuchung des Phasendiagramms RbCl/PbCl2

Bei der Neuuntersuchung des Phasendiagramms RbCl/PbCl2 mit differenzthermoanalytischen und rontgenographischen Methoden wurde die Bildung zweier ternarer, bisher noch nicht bekannter Phasen mit den Formeln Rb6Pb5Cl16 und Rb3PbCl5 gefunden, die beide in neuen Strukturtypen kristallisieren. Beide Phasen zersetzen sich peritektoid, die 6 : 5-Phase bei 350 °C und die 3 : 1-Phase bei 305 °C. Die Schmelzpunkte der kongruent schmelzenden bleireichen 1 : 2-Phase (RbPb2Cl5) und der 1 : 1-Phase (RbPbCl3) bei 420 °C bzw. 440 °C stimmen mit alterer Literatur recht gut uberein. RbPbCl3 wurde als eine nur bei hoheren Temperaturen stabile Phase identifiziert, die sich unterhalb 320 °C in die Nachbarphasen Rb6Pb5Cl16 und RbPb2Cl5 zersetzt. Fur die Verbindung Rb2PbCl4 konnte der inkongruente Schmelzpunkt auf 440 °C korrigiert werden, allerdings deutet sich bei tieferen Temperaturen zusatzlich eine Phasenumwandlung an. Redetermination of the Phase Diagram RbCl/PbCl2 A reinvestigation of the phase diagram RbCl/PbCl2 revealed the existence of two not yet known phases with the formula Rb6Pb5Cl16 and Rb3PbCl5. Both ternary compounds, which decompose peritectoidally at 350 °C for Rb6Pb5Cl16 and 305 °C for Rb3PbCl5, crystallize in new structure types. The points of congruent melting of the 1 : 2-phase (RbPb2Cl5) and of the 1 : 1-phase (RbPbCl3) at 420 °C and 440 °C respectively agree well with former specifications. But the transition of RbPbCl3 at 310 °C, described by Treis [1] could not be verified. RbPbCl3 is only stable at temperatures above 320 °C. For Rb2PbCl4 a point of incongruent melting was found at 440 °C and in addition a polymorphic transition may be inferred at lower temperatures.

Uncommon valence states in the metallic lanthanide and actinide diiodides MI2 (MLa, Ce, Nd, Gd and Th) and in the uranium tellurides UTe2, U2Te5 and UTe3 Part 2: The uranium tellurides UTe2, U2Te5 and α-UTe3

Abstract For the compounds UTe2, U2Te5 and α-UTe3 we describe the results of X-ray single crystal investigations, in the case of UTe2 as a function of temperature to detect phase transitions as indications for structural or electronical changes. The different types of distance alternation in linear tellurium chains, observed as common feature in all these polytelluric compounds, are discussed in terms of their electron count and atomic volume calculated from the Electron Localization Function ELF.

Combinatorial development of novel Pd based mixed oxide catalysts for the CO hydrogenation to methanol.

In a combinatorial study numerous palladium containing mixed oxides were synthesized by a sol-gel approach and screened for their catalytic activity toward methanol synthesis from synthesis gas. Several materials exhibited higher yields than comparable supported catalysts. Titanium based materials showed to be the most promising catalytic materials, which exhibited good selectivities for temperatures below 265 °C. The materials investigated are characterized by high specific surface areas and high pore volumes which seem to have a beneficial effect on the reactivity.