Raman, FTIR and Theoretical Evidence for Dynamic Structural Rearrangements of Vanadia/Titania DeNOx Catalysts

Insight into the selective catalytic reduction (SCR) of NO by NH₃ over vanadia/titania catalysts is obtained from a combination of Raman and FTIR spectroscopic investigations and density functional theory (DFT) calculations. Studies of the V–OH and V=O functional groups under different conditions coupled with calculations of the stability and mobility of H atoms provide evidence that dynamic structural rearrangements may occur during the SCR reaction. Hydrogen atoms are bonded more strongly to oxygen atoms that are coordinated to a single vanadium atom (V=O species), compared to bonding at oxygen atoms that are coordinated to multiple vanadium atoms (e.g., V–O–V species); and, activation energy barriers for hydrogen transfer from a V=O species to another V=O species and to a V–O–V species are estimated from DFT calculations to be 60 and 130 kJ/mol, respectively. This dynamic nature of hydrogen transfer between oxygen atoms having different coordination environments also appears to explain some of the spectroscopic changes observed for vanadia/titania catalysts having different vanadia loadings.     

Density functional calculations of elastic properties of portlandite, Ca(OH)2

The elastic constants of portlandite, Ca(OH)₂, are calculated by use of density functional theory. A lattice optimization of an infinite (periodic boundary conditions) lattice is performed on which strains are applied. The elastic constants are extracted by minimizing Hooke's law of linear elasticity, applying a least-square method. Young's modulus and bulk modulus are calculated from the stiffness matrix. The results are compared with the Brillouin zone spectroscopy results of F. Holuj et al. [F. Holuj, M. Drozdowski, M. Czajkowski, Brillouin spectrum of Ca(OH)₂, Solid State Commun., 56 (12) (1985) 1019-1021.]. An error estimate has been performed and the results are compared with experimental values.     

Conditional moment closure modelling of soot formation in turbulent, non-premixed methane and propane flames

Presented are results obtained from the incorporation of a semi-empirical soot model into a first-order conditional moment closure (CMC) approach to modelling turbulent, non-premixed methane-air and propane-air flames. Soot formation is determined via the solution of two transport equations for soot mass fraction and particle number density, with acetylene and benzene employed as the incipient species responsible for soot nucleation, and the concentrations of these calculated using a detailed gas-phase kinetic scheme involving 70 species. The study focuses on the influence of differential diffusion of soot particles on soot volume fraction predictions. The results of calculations are compared with experimental data for atmospheric and 3 atm methane flames, and propane flames with air preheated to 323 K and 773 K. Overall, the study demonstrates that the model, when used in conjunction with a representation of differential diffusion effects, is capable of accurately predicting soot formation in the turbulent non-premixed flames considered.     

Cu2+ Doped PVA Passivated ZnSe Nanoparticles-Preparation, Characterization and Properties

Cu²⁺ doped ZnSe nanoparticles are prepared by simple chemical method at room temperature with polyvinyl alcohol (PVA) as the passivating agent. The prepared sample is characterized by using X-ray diffraction, optical, photoluminescence, electron paramagnetic resonance (EPR) and FT-IR techniques. The average crystallite size is calculated from X-ray diffraction pattern and it is about 8 nm. The presence of the paramagnetic Cu²⁺ species in ZnSe is identified by optical and EPR measurements. The site symmetry for Cu²⁺ is ascribed as tetragonally distorted octahedral site symmetry. Crystal field, spin-Hamiltonian and bonding parameters are evaluated. Room temperature photoluminescence spectrum of Cu²⁺ doped ZnSe exhibits emission peaks at 343, 353 and 411 nm which corresponds to UV region at the excitation wavelength of 310 nm. FT-IR spectrum indicates the presence of various functional groups of PVA in ZnSe nanoparticles. Different physical parameters are also evaluated for the prepared sample.     

Curing of styrene‐free unsaturated polyester alkyd: synthesis,characterization and simulation

Experimental and simulation studies of the crosslinking process of styrene‐free unsaturated polyester (UP) alkyd chains are presented. The thermal and mechanical properties of the crosslinked UP alkyd are studied as a function of the peroxide concentration. The characterized and simulated thermoset matrix properties are compared. Simulation of the crosslinking reaction is used to improve the understanding of the process and to define the species involved in it. The main experimental characterization tools used were differential scanning calorimetry and dynamic mechanical analysis. The main simulation tools used were a Monte Carlo procedure for the crosslinking process and a density functional theory‐based quantum code for the scission process. Good agreement between the experimental and simulation results was achieved. Copyright © 2010 Society of Chemical Industry     

CO vibrational frequencies on methanol synthesis catalysts: a DFT study

Periodic, self-consistent density functional theory calculations are used to explain the observed decrease in the vibrational frequency of CO on methanol synthesis catalysts under severe reducing conditions (N.-Y. Topsøe, H. Topsøe, J. Mol. Catal. A Chem. 141 (1999) 95–105). Vibrational frequencies for CO on eight different models of the methanol synthesis catalyst surface have been determined. The calculated vibrational frequency of CO on Cu(111) (1/9 ML CO coverage) with 1/9 ML of Zn adatoms shows a decrease of between 15 and 38 cm⁻¹ from the corresponding calculated CO frequency on clean Cu(111) (2073 cm⁻¹). The calculated vibrational frequency of CO on Cu(111) with 1/9 ML of ZnO species shows a decrease of up to 72 cm⁻¹ from the CO stretch frequency on clean Cu(111). These calculated CO vibrational frequency decreases agree with the experimentally measured decrease (ca. 50 cm⁻¹), suggesting that Zn and/or ZnO species may be present in the vicinity of active Cu sites of methanol synthesis catalysts under highly reducing conditions. In addition, CO vibrational frequencies on partially oxidized Cu(111) surfaces are shown to increase from the corresponding frequencies on clean Cu(111), in agreement with experimental results.     

Electronic structure and conformations of ortho-, meta-, and para-aminobenzensulfonic acid and its dimers

Geometric and electronic structures of some aniline derivatives have been obtained, aimed at a microscopic explanation of the observed electropolymerizability of these compounds. Monomers, dimers and their corresponding free radicals and ionic species, with the sulfonic acid group substituent located at various positions on the benzenoid ring, are considered. In this work we present an ab initio post-Hartree-Fock and density functional study of the ortho-, meta- and para-isomer of aminobenzenesulfonic acid (ortho-, meta-, and para-ABSA). To envisage a possible coupling scheme between ABSA molecules, we have obtained the equilibrium geometry and the electronic structure for monomers and dimers of ABSA as well as for the corresponding free radicals and ions.Based on the monomer-optimized geometries, atomic charges, bond orders and spin densities, a coupling scheme in the electrochemical polymerization is suggested. We have also calculated band gaps and ionization potentials. Some comments concerning the different theoretical methods used are made.     

The adsorption of methyl nitrite on the Au(111) surface

The interaction of the methyl nitrite molecule (CH₃ONO) with the gold(111) surface has been studied by means of density functional calculations. The perfect Au(111) surface has been represented by a rather large cluster model, Au₂₂, that was in turn used to extract information about the preferred adsorption geometry of the CH₃ONO species. Vibrational frequencies and adsorption energy are also reported. The calculated adsorption energies are 31.2 kJ/mol with respect to gas phase cis-conformer and 35.1 kJ/mol with respect to trans-methyl nitrite, very close to the experimental adsorption energy of 33.5 kJ/mol. From the analysis of vibrational frequencies of gas phase and adsorbed species it is concluded that only the cis-conformer is present at the Au(111) surface.     

Triglyceride composition of ewe,cow, and goat milk fat

The separation and identification of the components in milk fat, which are mainly triglycerides, is a challenge due to its complex composition. A reverse-phase high-performance liquid chromatography (HPLC) method with gradient elution and light-scattering detection is described in this paper for the triglyceride analysis in ewes’ milk fat. Triglyceride identification was carried out by combining HPLC, gas-liquid chromatography (GLC), and the calculated equivalent carbon numbers of several triglyceride standards. Quantitation of partially resolved peaks in the HPLC chromatogram was accomplished by applying a peak deconvolution program. Forty-four fatty acids were identified by GLC analysis, but only 19 were used for the following prediction of triglyceride molecular species; 181 triglycerides were identified, some of which were grouped at the same peak and needed application of the deconvolution program. Consequently, coefficients of variation were close to or lower than 5%. Moreover, the triglyceride composition of ewe, cow, and goat milk fat were compared by using these methods. These results show that ewe milk fat is richer in short- and medium-chain triglycerides, and cow milk fat is richer in long-chain and unsaturated triglycerides.     

Study of the Experimental and Simulated Vibrational Spectra Together with Conformational Analysis of Thioether Cyanobiphenyl-Based Liquid Crystal Dimers

Infrared spectroscopy (IR) and quantum chemistry calculations that are based on the density functional theory (DFT) have been used to study the structure and molecular interactions of the nematic and twist-bend phases of thioether-linked dimers. Infrared absorbance measurements were conducted in a polarized beam for a homogeneously aligned sample in order to obtain more details about the orientation of the vibrational transition dipole moments. The distributions to investigate the structure and conformation of the molecule dihedral angle were calculated. The calculated spectrum was compared with the experimental infrared spectra and as a result, detailed vibrational assignments are reported.     

Potential of Oilseeds Native to Amazon and Brazilian Cerrado Biomes: Benefits,Chemical and Functional Properties,and Extraction Methods

The primary objective of this study was to shed greater light on the characteristics and multifaceted potential of oil extracts from kernels of Bertholletia excelsa (Brazil nut), seeds of the Plukenetia species and Caryocar species. These are but a few of the multitude of the plant species found in the Amazon and Brazil's Cerrado biomes. They have many substantial organoleptic, nutritional, and functional properties that are comparable or exceed better known oils, and they manifest health benefits and prospective economic opportunities as an oil source for foods, pharmaceutical, and cosmetic industries. It is also hoped that this study gives rise to further research that may be beneficial to the industry and improve the local economies where these raw materials are found.     

GC/MS and DFT studies of S,S-dialkyl methylphosphonothioloselenoates related to Schedule 2.B.04 of Chemical Weapons Convention

ABSTRACT

Due to the internationally sensitive nature of the verification process, unambiguous structural identification of Chemical Weapons Convention (CWC)-related chemicals in a sample of a suspected agent is necessary. Therefore, the availability of mass spectra, retention indices, and interpretation skills are essential needs. S,S-dialkyl methylphosphonothioloselenoates belong to scheduled 2.B.04 of the CWC, but there are no analytical data for these compounds in the literature. The title compounds are prepared through microsynthetic protocols, and the results of their mass spectra are studied by electron ionization (EI) method. Schemes for the fragmentation of the compounds are proposed. The retention indices (RI) of the synthesized compounds are also calculated using Van den Dool’s method. The correlation of RI and calculated polarizability data is investigated by density functional theory calculations. EI mass spectra and RI values enable structural identification of all the studied isomeric compounds.     

气体、溶液中的非电解质和电解质在多孔颗粒内扩散的对比研究

实验测量了气体、溶液中的非电解质以及电解质三类性质相差较大的体系在相同的多孔颗粒内(孔隙率0.234～0.632)的有效扩散系数,并计算出曲折因子.探讨了由D_(?)=D_oε/τ定义的曲折因子对孔隙结构和扩散组分特性的依赖关系.     

Native Liquid Chromatography and Mass Spectrometry to Structurally and Functionally Characterize Endo-Xylanase Proteoforms

Xylanases are of great value in various industries, including paper, food, and biorefinery. Due to their biotechnological production, these enzymes can contain a variety of post-translational modifications, which may have a profound effect on protein function. Understanding the structure–function relationship can guide the development of products with optimal performance. We have developed a workflow for the structural and functional characterization of an endo-1,4-β-xylanase (ENDO-I) produced by Aspergillus niger with and without applying thermal stress. This workflow relies on orthogonal native separation techniques to resolve proteoforms. Mass spectrometry and activity assays of separated proteoforms permitted the establishment of structure–function relationships. The separation conditions were focus on balancing efficient separation and protein functionality. We employed size exclusion chromatography (SEC) to separate ENDO-I from other co-expressed proteins. Charge variants were investigated with ion exchange chromatography (IEX) and revealed the presence of low abundant glycated variants in the temperature-stressed material. To obtain better insights into the effect on glycation on function, we enriched for these species using boronate affinity chromatography (BAC). The activity measurements showed lower activity of glycated species compared to the non-modified enzyme. Altogether, this workflow allowed in-depth structural and functional characterization of ENDO-I proteoforms.     

Quantum chemical calculations of the thermochemistry of tantalum oxyhydroxide species

Tantalum pentoxide and water vapor are predicted to react at elevated temperatures to form TaO(OH)₃(g), TaO₂(OH)(g), and Ta(OH)₅(g). The thermochemistry of these species is calculated with quantum chemistry methods. Geometries and vibrational frequencies are determined from B3LYP DFT methods. Energetics are calculated from high levels of theory—CCSD(T) and larger basis sets for Ta, O, and H. We report the enthalpies of formation at 0 K and 298.15 K, entropy at 298.15 K, and heat capacity. These quantities are used to calculate vapor pressures at 1400-1800 K and 50% water vapor. TaO(OH)₃(g) is found to be the dominant species. The calculated vapor pressure of TaO(OH)₃(g) is converted to a vapor flux and compared to previous experimental flux measurements from a flat plate in a slowly flowing H₂O/Ar gas and also vapor flux from a steam jet experiment. These “open system” experiments result in lower fluxes that are within 1.12-17X of the calculated equilibrium fluxes. This suggests that the experimental measurements are near equilibrium or have a small kinetic barrier.     

Use of 300,000 pseudo-experimental data over 1800 pure fluids to assess the performance of four cubic equations of state: SRK,PR, tc-RK,and tc-PR

The guidelines to constitute a database containing, for 1800 pure fluids, more than 300,000 pseudo-experimental vapor pressure, liquid density, enthalpy of vaporization, and liquid heat capacity data are described. Such a database provides a tool for a fair assessment of the performances of equations of state to correlate (or predict) the properties of pure components. In this paper, we use it to assess the performance of four cubic equations of state (CEoSs): original Soave–Redlich–Kwong (SRK), original Peng–Robinson (PR), and the translated-consistent versions of PR (tc-PR) and RK (tc-RK). The deviations between calculated and experimental data are compared for the four CEoSs, which make it possible to discuss the influence of the α-function on the calculated vapor–liquid equilibrium properties and how the volume translation impacts the calculated volumetric properties. Eventually, the 1800 pure components are divided into 1252 non-self-associating and 548 self-associating compounds, and the accuracy of the CEoSs depending on the associating character of the molecules is discussed.     

Tricarbonyl rhenium complex of 2,2′-bis(4,5-dimethylimidazole) — Synthesis,spectroscopic characterization,X-ray structure and DFT calculations

The paper presents a combined experimental and computational study of the tricarbonyl rhenium(I) complex incorporating 2,2′-bis(4,5-dimethylimidazole) (tmbiimH₂). The complex has been studied by IR, UV–Vis spectroscopy and X-ray crystallography. The electronic structure of [Re(CO)₃(tmbiimH₂)Cl] has been calculated with the density functional theory (DFT) method, and the electronic spectrum of the complex was investigated at the TDDFT level employing B3LYP functional in combination with LANL2DZ.     

Elastic and electronic properties of XB2 (X=V,Nb, Ta,Cr, Mo,and W) with AlB2 structure from first principles calculations

The crystal structure, electronic properties, mechanical properties, and anisotropy of XB₂ (X=V, Nb, Ta, Cr, Mo, and W) were calculated by first principles calculations based on density functional theory (DFT) with the generalized gradient approximation (GGA). The results are in good agreement with available theoretical and experimental values. The calculated cohesive energy and formation enthalpy indicate that they are thermodynamically stable structures. The elastic constants satisfy all of the mechanical stability criteria. The mechanical moduli were predicted by the Voigt–Reuss–Hill approximation. The mechanical anisotropy was indicated by the surface constructions of Young's moduli, and the results show that anisotropy of WB₂ is stronger than others. The electronic structure indicates that the bonding behaviors of XB₂ (X=V, Nb, Ta, Cr, Mo, and W) are the combinations of covalent and metallic bonds. The hardness of the borides was also evaluated, and the result reveals that TaB₂ is the hardest compound among them.