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Quantum Chemical Approach (quantum + chemical_approach)
Selected AbstractsHydrodenitrification with PdCu Catalysts: Catalyst Optimization by Experimental and Quantum Chemical ApproachesISRAEL JOURNAL OF CHEMISTRY, Issue 1 2006Irena Efremenko A continuous process for nitrate and nitrite abatement from drinking water by catalytic hydrogenation has been developed in our lab. We describe the experimental process development procedure, and support it with semiempirical quantum chemical methods. Comparisons of activated carbon (ACC) and silica glass fiber (GFC) cloths as supports for mono- and bimetallic Pd-Cu catalysts show the former to be 45-fold and 15-fold more active for nitrite and nitrate hydrogenation, respectively, than the latter. Catalysts prepared by selective deposition of Cu on Pd/ACC led to better activity for nitrate hydrogenation than catalysts prepared by co-impregnation or ion exchange methods. The optimal Cu:Pd atomic ratio was found to be 1:2. The computational results show the following: (i) The dispersion of Pd catalysts supported on ACC is much higher than that on GFC due to the larger surface area and higher density of adsorption sites, and that accounts for the higher activity of PdCu/ACC; (ii) Nanosized Pd particles supported on ACC have a semispherical shape and possess preferentially close-packed triangular surfaces, while Pd/GFC particles are extended in the direction parallel to the support surface and show both fcc (100) and (111) planes; (iii) The interaction of Cu atoms with both supports is stronger than that of Pd; adsorbed Cu atoms show a greater ability to form monometallic than bimetallic bonds and that should result in poor mixing of the metal upon co-impregnation, as was observed experimentally; (iv) Cu atoms in bimetallic PdCu particles admit a significant positive charge; the experimentally measured solubility of metal atoms correlates with their calculated charges. The best catalyst (2 wt%Pd-0.6 wt%Cu/ACC) was employed in a novel continuous flow reactor for nitrate hydrogenation in distilled and tap water. The advantages of the reactor investigated over a conventional packed bed reactor are discussed, suggesting a potential for further process intensification. [source] Heuristic molecular lipophilicity potential (HMLP): Lipophilicity and hydrophilicity of amino acid side chainsJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 6 2006Qi-Shi Du Abstract Heuristic molecular lipophilicity potential (HMLP) is applied in the study of lipophilicity and hydrphilcity of 20 natural amino acids side chains. The HMLP parameters, surface area Si, lipophilic indices Li, and hydrophilic indices Hi of amino acid side chains are derived from lipophilicity potential L(r). The parameters are correlated with the experimental data of phase-transferring free energies of vapor-to-water, vapor-to-cyclohexane, vapor-to-octanol, cyclohexane-to-water, octanol-to-water, and cyclohexane-to-octanol through a linear free energy equation ,G°tr,i = b0 + b1Si+ + b2Si, + b3Li + b4Hi. For all above six phase-transfer free energies, the HMLP parameters of 20 amino acid side chains give good calculation results using linear free energy equation. HMLP is an ab initio quantum chemical approach and a structure-based technique. Except for atomic van der Waals radii, there are no other empirical parameters used. The HMLP has clear physical and chemical meaning and provides useful lipophilic and hydrophilic parameters for the studies of proteins and peptides. © 2006 Wiley Periodicals, Inc. J Comput Chem 27: 685,692, 2006 [source] Formation of Superoxo Species by Interaction of O2 with Na Atoms Deposited on MgO Powders: A Combined Continuous-Wave EPR (CW-EPR), Hyperfine Sublevel Correlation (HYSCORE) and DFT StudyCHEMISTRY - A EUROPEAN JOURNAL, Issue 23 2010Francesco Napoli Dr. Abstract The formation of O2, radical anions by contact of O2 molecules with a Na pre-covered MgO surface is studied by a combined EPR and quantum chemical approach. Na atoms deposited on polycrystalline MgO samples are brought into contact with O2. The typical EPR signal of isolated Na atoms disappears when the reaction with O2 takes place and new paramagnetic species are observed, which are attributed to different surface-stabilised O2, radicals. Hyperfine sublevel correlation (HYSCORE) spectroscopy allows the superhyperfine interaction tensor of O2,Na+ species to be determined, demonstrating the direct coordination of the O2, adsorbate to surface Na+ cations. DFT calculations enable the structural details of the formed species to be determined. Matrix-isolated alkali superoxides are used as a standard to enable comparison of the formed species, revealing important and unexpected contributions of the MgO matrix in determining the electronic structure of the surface-stabilised Na+O2, complexes. [source] Mass-selective vibrational spectroscopy of vanadium oxide cluster ionsMASS SPECTROMETRY REVIEWS, Issue 4 2007Knut R. Asmis Abstract A corner stone in the study of the size-dependent properties of cluster ions in the gas phase is their structural characterization. Over the last 10 years, significant progress has been in this research field because of significant advances in the gas phase vibrational spectroscopy of mass-selected ions. Using a combination of modern experimental and quantum chemical approaches, it is now in most cases possible to uniquely identify the geometric structure of cluster ions, based on the comparison of the experimental and simulated infrared spectra. In this article, we highlight the progress made in this research area by reviewing recent infrared photodissociation (IR-PD) experiments on small and medium sized (up to 30 atoms) vanadium oxide ions. © 2007 Wiley Periodicals, Inc., Mass Spec Rev. [source] | ||||||||||