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Hanau am Main, Germany

Franke R.,Evonik Industries | Franke R.,Ruhr University Bochum | Hannebauer B.,AQura GmbH
Physical Chemistry Chemical Physics | Year: 2011

This paper examines how the accuracy of activity coefficients at infinite dilution calculated from the conductor-like screening model for real solvents (COSMO-RS) depends on the basis set and the quantum chemical method used. Activity coefficients at various temperatures serve as experimental parameters for optimising the COSMO-RS parameters. A modification of the electrostatic misfit term of the energy function of COSMO-RS is presented that leads to a slightly higher accuracy. COSMO-RS parameter sets for nine different systematically varied basis sets using the density functional theory with the BP86 functional show that at least a valence double-zeta basis set is necessary for good accuracy. Larger basis sets show no advantages. Investigations of eight different quantum chemical calculation methods using a valence triple-zeta basis set are documented. Hartree-Fock and local density approximations give relatively poor results. The gradient-corrected density functionals investigated and the B3LYP hybrid functional show practically identical accuracy. The most accurate parameterisation was obtained with MP2. © 2011 the Owner Societies.

Albers P.W.,AQura GmbH | Mobus K.,Evonik Industries | Frost C.D.,Rutherford Appleton Laboratory | Parker S.F.,Rutherford Appleton Laboratory
Journal of Physical Chemistry C | Year: 2011

The proton dynamics of palladium catalysts on activated carbon, of palladium on calcium carbonate, and of lead-modified palladium on calcium carbonate (the Lindlar-catalyst), hydrogenated in situ to comparable equilibrium pressure, were measured by means of inelastic incoherent neutron scattering. Isolated primary particles of palladium of ~3.2 nm size showed a lower degree of formation of β-phase hydride than 10-15 nm sized aggregates, which were formed from ~3.7 nm primary particles of palladium. The addition of lead to the palladium on calcium carbonate in catalysts of identical primary particle size (3.7 nm) and shape caused a decrease in the β-phase hydride formation by a factor of 2. For the catalyst selectivity in the hydrogenation of triple to double bonds not only the presence of modifiers at the surface but also a reduced, moderated hydrogen storage function is of relevance. © 2011 American Chemical Society.

Franke R.,Evonik Industries | Franke R.,Ruhr University Bochum | Hannebauer B.,AQura GmbH | Jung S.,TU Dortmund
Fluid Phase Equilibria | Year: 2013

The COSMO-RS method allows mixed-phase thermodynamic parameters to be calculated from quantum-chemically determined surface screening charge-density distributions. For this method we shall present and discuss a parameterization for alkanes and olefins in alcohols, which are important classes of molecules in industrial application. As we were able to demonstrate, the accuracy of predicting from a specialized parameterization can be significantly better than that from a universal parameterization. Furthermore, we critically compared the method with the UNIFAC(Do) group contribution method. © 2012 Elsevier B.V..

Mobus K.,Evonik Industries | Grunewald E.,Evonik Industries | Wieland S.D.,Evonik Industries | Parker S.F.,Rutherford Appleton Laboratory | Albers P.W.,AQura GmbH
Journal of Catalysis | Year: 2014

The influence of alloying supported palladium particles of 2 nm size with platinum and iron on the catalytic activity for the selective hydrogenation of nitrobenzene (NB) was studied. We show that the use of a carbon black support of enhanced sp2 character has a marked 'templating' effect on the location of the palladium particles, which are preferentially deposited at the edge sites of the carbon support surface. Alloying with platinum and iron leads to disaggregation down to isolated primary particles, and this has a major effect on the catalytic activity (Pd 6.6, PdPt 36.9, PdPtFe 23.1 mmol NB min-1), as well as on the relative amounts of β-palladium hydride formed (normalized peak integrals: Pd 127.0, PdPt 87.6, PdPtFe 27.2). The results enable a greater understanding of how better performance can be obtained in catalysts by appropriate choice of support, particle size, alloying and adjustment of hydrogen storage capability. © 2013 Elsevier Inc. All rights reserved.

Parker S.F.,Rutherford Appleton Laboratory | Lennon D.,University of Glasgow | Albers P.W.,AQura GmbH
Applied Spectroscopy | Year: 2011

Inelastic neutron scattering spectroscopy (INS) has enabled vibrational spectra to be measured for over 50 years. Most studies have used a type of spectrometer that is straightforward to build and use and that provides spectra that are not dissimilar to infrared and Raman spectra. In this Focal Point Review Article we show the advantages of a type of neutron vibrational spectrometer that has been largely unknown to the spectroscopy community. These instruments are able to access regions of low momentum transfer at relatively large energy transfer. This means that the C-H, N-H, and O-H stretch regions can be exploited by INS spectroscopy for the first time. The instruments generally have very large detector area, which means that they are significantly more sensitive than the more commonly used instruments. They also allow the energy transfer as a function of momentum transfer to be examined. After briefly outlining the basics of INS spectroscopy, we describe the operational principles of the instruments and show how flux and resolution can be traded. We then review how the advantages of the instruments can be used to gain understanding of molecular systems in areas as diverse as hydrogen storage, hydrogen bonding, and fullerenes. The instruments are starting to have a significant impact in studies of catalysts and this is illustrated with recent studies of hydrogen on fuel cell catalystsmethyl chloride synthesis, the deactivation of methane reforming catalysts, and a model carbon monoxide oxidation catalyst. © 2011 Society for Applied Spectroscopy.

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