Effect of Cesium and Phosphate Addition to Mo/V/W Mixed Oxide Catalysts for the Gas Phase Oxidation of Methacrolein to Methacrylic Acid

The present study investigates modified Mo/V/W mixed oxides as a possible alternative for state of the art heteropoly acid catalysts (HPA) in the partial oxidation of methacrolein (MAC) to methacrylic acid (MAA). Even though HPAs show an excellent activity and MAA selectivity, their long-term stability is unsatisfying, rendering the catalyst inoperable after runtimes of roughly 6 months. Mo/V/W mixed oxides consisting of M1 and a hexagonal (Mo,V,W)O$_{x}$-phase (h-phase) in varying proportions were modified by impregnation with aqueous solutions containing cesium and phosphate ions. All samples were characterized with respect to specific surface area, crystallinity, elemental and phase composition. The catalytic performance in the oxidation of MAC to MAA was investigated using a continuously operated reaction unit with tubular fixed bed reactor. Impregnation with cesium and phosphate ions and subsequent heating triggers the transformation of the mixed oxide into a Keggin-type HPA, whereby the h-phase is more reactive than M1. The transformation into HPA is accompanied by a change in the catalytic properties, i.e., the selectivity to MAA is considerably improved. Compared to HPA synthesized directly, however, the HPA samples obtained by transformation of mixed oxides exhibit no advantages, be it with respect to activity, MAA selectivity or stability

Facile template-free synthesis of multifunctional 3D cellular carbon from edible rice paper

Edible rice paper wrapper is found to be an interesting precursor of a porous and light-weight carbon material. During pyrolysis, material samples show significant differences in length change, displaying typical 20–25% shrinking in the in-plane directions, and strongly expanding (up to 500%) across their out-of-plane direction. This results in a template-free synthesis of a 3D network of cellular carbon material. The out-of-plane expansion also allows for fabrication of 3D shapes of cellular carbon material from the 2D precursor. The rice paper derived carbon material features a hierarchical porosity, resulting in a specific surface area ranging from 6 m(2) g(−1) to 239 m(2) g(−1) depending on the synthesis temperature. The carbon material has a density of 0.02–0.03 g cm(−3), and a higher modulus-density ratio than reported for other cellular carbon materials. It is mechanically stiff and exhibits excellent fire-resistant properties

Pseudopeptidic ligands: exploring the self-assembly of isopthaloylbisglycine (H2IBG) and divalent metal ions

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Cation diffusion patterns across the magneto-structural transition in Fe7S8

Migration of atoms in solids during diffusion-dependent reactions is relatively fast and generally not directly recordable in experiments. Here we present an experimental framework that includes fast differential scanning calorimetry to resolve cation-migration paths in crystalline solids using the reversible magneto-structural transition of 4C to 1C pyrrhotite as a testbed. The transition between these two polymorphic Fe7S8 phases at about 600 K is a diffusive process of vacancies, respectively of Fe in octahedral interstitial sites within a hexagonal close-packed lattice of sulfur, and it coincides with the Curie temperature of 4C pyrrhotite. The Fe cations migrate along three kinds of diffusion paths, and their enthalpy contributions to the total reaction enthalpy are taken to define the diffusion patterns in the endothermic reaction and the exothermic back-reaction, respectively. Our experimental findings provide insight into the potential of diffusion patterns to disentangle ordering mechanisms in solids.ISSN:1463-9084ISSN:1463-907

Solubility of Calcined Kaolinite, Montmorillonite, and Illite in High Molar NaOH and Suitability as Precursors for Geopolymers

Clays and clay minerals dissolve over a broad pH range, such as during sediment diagenesis and in a variety of applications, including nuclear waste storage, landfills, and geopolymer binders in the construction industry. The solubility depends on process parameters (pH, temperature, pressure, etc.) and material properties (phase content, clay mineral composition, particle size, etc.). Pretreatments such as calcination or severe grinding change the material properties and could enhance solubility, which is called activation. The aim of the current study was to determine the solubility of three different clay minerals after calcination (metakaolinite, metamontmorillonite, and metaillite) in high molar alkaline solutions (NaOH) up to 10.79 mol/L and pH = 14.73. Furthermore, the solubility of an Al(OH)3 powder in alkaline solution (NaOH) was analyzed, as it can be used to adjust the Si:Al ratio of geopolymer precursors. The residues of the clay minerals after the alkaline treatment were investigated to disclose potential alterations in their phase contents. Based on the results of the thermal and alkaline activation, conclusions about the suitability as geopolymer precursors were made. All clay minerals showed an increase in solubility proportional to the concentration of the alkaline solution. The solubility decreased in the order metakaolinite > metamontmorillonite > metaillite. Thereby, dissolution was incomplete for all three clay minerals (<90%) after 7 days and congruent for metakaolinite and metaillite but incongruent for metamontmorillonite

Moisture adsorption and desorption behavior of raw materials for the t-rtm process

The use of fiber reinforced plastics (FRPs) has significant potential to reduce the weight of components. As regards the sustainability of these components, thermoplastic matrices offer more potential for recycling than thermoset ones. A possible manufacturing process for the production of thermoplastic FRPs is thermoplastic resin transfer molding (T-RTM). In this very moisture-sensitive process, ε-caprolactam in addition to an activator and catalyst polymerizes anionically to polyamide 6 (aPA6). The anionic polymerization of aPA6 is slowed down or even completely blocked by the presence of water. This study analyses the sorption behavior of the matrix, fiber, binder and core materials for the production of anionic polyamide 6 composites, which are processed in the thermoplastic RTM process. Water vapor sorption measurements are used to determine the adsorption and desorption behavior of the materials. The maximum moisture loading of the materials provides information about the water adsorption capacity of the material. This knowledge is crucial for correct handling of the materials to achieve a fast process and good properties of the final product