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CrOx/La2O3 mixed oxides, prepared by impregnating La2O3 with appropriate aqueous solutions of (NH4)2CrO4 and calcining at 600 °C for 4 h, have been investigated by means of XRD, TPR, XPS, DRIFTS, and Raman spectroscopy (RS). The formation of the compounds La2CrO6, La(OH)CrO4 and LaCrO4 under these conditions was evidenced. Strong peaks at 864, 884, 913, and 921 cm-1, as well as weak peaks at 136, 180, 354, 370, and 388 cm-1 in the RS spectrum of CrOx/La2O3 have been assigned to La2CrO6.
Selective Catalytic Reduction of Nitric Oxide by Ammonia over Egg-Shell MnOx/NaY Composite Catalysts
(2002)
A novel composite catalyst system for the selective catalytic reduction (SCR) of NOx by NH3 is described operating at temperatures lower than 470 K in the presence of water with NO conversions of 80100% at space velocities of 30,00050,000 h-1. The catalyst is prepared by egg-shell precipitation of MnO2 on the external surface of zeolite NaY. Structural and thermal stability of precipitated MnO2 as well as of the MnO2/NaY composite catalyst were characterized by N2 adsorption, X-ray diffraction, laser Raman spectroscopy, temperature-programmed reduction, and electron microscopy. MnO2 precipitated on zeolite NaY (15 wt% loading) retained its amorphous state up to calcination temperatures of 775 K. The zeolite component remained structurally intact. Calcination at higher temperatures destroyed the zeolite structure and transformed MnO2 into Mn3O4. DRIFT spectroscopic investigations revealed the presence of symmetric O=NON=O species formally corresponding to N2O3 on the composite catalyst after contact with NO. Catalytic measurements under integral flow conditions showed that the catalyst performance is associated with a close coupling of nitrite formation and its drain off from equilibria with NO/NO2 and nitrate by ammonia. Several results are in line with the diazotation mechanism, including NH3 protonation to NH4+, whereas prevailing Lewis acid sites should enable NH3 activation via amide species, thus leading to a parallel amide/nitrosamide SCR reaction route. The activity-temperature profile fulfills the requirements of a low-temperature NOx reduction catalyst for mobile diesel engines if an ammonia supply is implemented on board, e.g., by urea decomposition.
A closed pressure vessel test (CPVT) screen for explosive properties of energetic organic compounds
(2007)
Results of a round-robin test on a mini-autoclave are reported and previously proposed criteria reviewed. Criteria based upon the results for three standard materials are now put forward. These standards-based criteria, in contrast to numerical criteria, theoretically allow any laboratory to utilize the data accumulated to date, irrespective of the equipment used. The practical requirement is that adequate discrimination can be achieved. Data to assess this are given.
Sol-gel preparation of calcium titanium phosphate: viscosity, thermal properties and solubility
(2012)
Calcium titanium phosphate (CTP) was prepared by the sol–gel route in order to prepare suitable coatings. This work addresses the question of how to prepare stable CTP sols. Their rheological properties as a function of process parameters like solid loading and water content are investigated. It was found that an increased solid loading as well as an increased water content lead to an increased initial viscosity as well as a more pronounced ageing induced viscosity rise. In addition, the thermal behavior of the resulting xerogels was analyzed. Furthermore, we studied the ion release behavior of the xerogels when brought in contact with water. Results suggest that calcium titanium phosphate shows a diffusion controlled ion release mode with a preferential release of Ca.
Abstract While classically used to visualise the magnetic microstructure of functional materials (e.g., for magnetic applications), in this study, the Bitter technique was applied for the first time to visualise macroscopic deformation gradients in a polycrystalline low-carbon steel. Spherical indentation was chosen to produce a multiaxial elastic–plastic deformation state. After removing the residual imprint, the Bitter technique was applied, and macroscopic contrast differences were captured in optical microscopy. To verify this novel characterisation technique, characteristic “hemispherical” deformation zones evolving during indentation were identified using an analytical model from the field of contact mechanics. In addition, near-surface residual stresses were determined experimentally using synchrotron radiation diffraction. It is established that the magnetic domain distribution contrast provides deformation-related information: regions of different domain wall densities correspond to different “hemispherical” deformation zones (i.e., to hydrostatic core, plastic zone and elastic zone, respectively). Moreover, the transitions between these three zones correlate with characteristic features of the residual stress profiles (sign changes in the radial and local extrema in the hoop stress). These results indicate the potential of magnetic domain distribution imaging: visualising macroscopic deformation gradients in fine-grained ferromagnetic material with a significantly improved spatial resolution as compared to integral, mean value-based measurement methods.
Conventional simultaneous thermal analysis, capillary-coupled TGMS, 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.
Nonequilibrium vibrational excitations of para-nitroaniline (PNA, 4-nitroaniline) occurring after internal conversion from the photoexcited charge transfer state are studied by picosecond anti-Stokes Raman scattering. Vibrational excess populations with distinctly different picosecond rise and decay times are found for a number of modes with frequencies between 860 and 1510 cm1, including the overtone of a non-Raman active mode. A nonthermal distribution of vibrational populations exists up to about 6 ps after photoexcitation. The time-resolved experiments are complemented by steady-state infrared and Raman measurements as well as calculations based on density functional theory, providing a detailed analysis of the steady-state vibrational spectra of PNA and two of its isotopomers. A weakly Raman active vibration at about 1510 cm1 displays the fastest rise time and a pronounced excess population andthusrepresents the main accepting mode. We suggest that an out-of-plane mode giving rise to the overtone Raman band at this frequency acts both as coupling and accepting mode in the internal conversion process.