Alkylation of the toluene methyl group: A DFT study

Alkylation of the methyl group of toluene was modeled at the B3LYP/6-311++G⁷ level. In the presence of Na₂; the model basic catalyst, the methyl group is more active for the Na/H exchange than the H atoms at the aromatic ring. The PhCH₂Na molecule formed is next alkylated by ethene to produce PhC₃H₆Na. This needs a 30 kcal/mol barrier to be overcome. Finally, the Na/H exchange between PhC₃H₆Na and (unreacted) toluene molecules proceeds through a 18 kcal/mol barrier and ca. 10 kcal/mol is released. The study has confirmed the basic alkylation scheme proposed by Pines, Vesely, and Ipatieff more than 50 years ago.     

A DFT study on benzene adsorption over tungsten sulfides: surface model and adsorption geometries

Benzene adsorption on a WS₂(100) surface was studied by ab initio periodic DFT computations. Benzene adsorption is facile on the bridge site of the bare W edge via η² or η³ coordination. Taking into account the stable configuration at the W edge under typical hydrotreating reaction conditions (623 K, H₂S/H₂ = 0.01), benzene adsorption is found to be difficult, even when defective bridge sites are created.     

A Lagrangian model for spray behaviour within vine canopies

This work concerns the numerical prediction of pesticide deposits on vine by air assisted sprayers. This numerical model consists in two different parts: the air flow characteristics were obtained through a Navier–Stokes solver in which additional terms have been introduced in order to account for the modification of the flow by the vine foliage. The theoretical form of these terms was derived through an averaging procedure. As a result, the canopy effect was modelled by introducing momentum and turbulence source terms in the Navier–Stokes equations. The constants were identified thanks to experimental data obtained by direct measurements of the air flow speeds through an artificial canopy. The second part of the model consists in simulating the droplet cloud by means of a lagrangian stochastic model. The average motion of the droplets was computed through the use of lagrangian coordinates and the turbulence effect on the droplets was interpreted in term of statistical properties of the droplet cloud. The tractor displacements were accounted for through unsteady boundary conditions. Once the size and the droplets cloud locations have been determined, the deposit was predicted for a vine row of one meter length using an efficiency coefficient obtained from simulations. Thanks to this approach we were able to quantify the effect of air turbulence on droplet deposition.     

Thermochemistry of biodiesel oxidation reactions: A DFT study

Density functional theory (DFT) quantum chemical calculations have been used to evaluate the gas phase electronic and thermochemical properties of fatty acid esters. The calculated low relative energies of the corresponding radicals can explain the large variety of oxidation products observed in experiments. The first oxidation reaction step was determined to be non-spontaneous for all fatty acid esters studied. Ethyl and methyl esters showed similar susceptibilities to oxidation in the gas phase. All subsequent reaction steps leading to the secondary products of oxidation were observed to be spontaneous. The thermochemical stability order of one double bond oxidation in the gas phase was determined to be linoleate < γ-linolenate < α-linolenate < oleate < ricinoleate. Therefore, biodiesel produced from castor oil could be used as an additive to biodiesel produced from other vegetable oil sources in order to improve the oxidation stability properties of the final fuel blend.     

DFT investigation of the regiospecificity of a model catalyst site for propene polymerisation

Density functional theory calculations were used to study the mechanism of regioregular and regioirregular propene insertions to a model catalyst site (TiMg₂Cl₆CH₃). Further regioregular insertions to Ti-2-butyl and Ti-2-methylpropyl bonds were simulated to study the reactivity after the first insertions. It was found that after the first regioregular insertion there exists two minimum energy conformations for the chain: α-agostic and β-agostic. The formation of a π-complex between propene and the active site was only possible with the α-agostic conformation. After the regioirregular insertion there is no minimum energy conformation with α-agostic interaction and so further insertions are hindered. In contrast to propene, ethene is found to be able to coordinate also to β-agostic site and is therefore able to reactivate polymerisation after a regioirregular insertion.     

Proton abstraction ability of MgO: a DFT cluster model study of the role of surface geometry

Methanol and isocyanic acid adsorptions on a defective MgO surface have been studied. Equilibrium geometries, adsorption energies, atomic and molecular charges and electronic densities were obtained using a density functional theory method. Oxide surface atoms with different coordination numbers show very different reactivity giving both molecular and dissociated adsorbed species. The methanol molecule requires lower coordination numbers of the active site than the isocyanic acid molecule for dissociative adsorption. The role of the acidic and basic sites has been considered and analyzed in terms of natural bond orbital charges. The main vibration frequencies have been compared with available infrared spectroscopic data.     

A DFT study on poly(lactic acid) polymorphs

Poly(lactic acid) (PLA) can crystallize in α-, β-, γ- and stereocomplex (sc)- forms. It has been shown that the formation of stereocomplex between poly(l-lactic acid) and poly(d-lactic acid) significantly improve thermal stability and mechanical properties. However the mechanisms of enhancements are still unclear. In this study, we investigate the PLA polymorphs from the first-principles theoretical perspective in order to understand the intermolecular interaction in the crystals. Density functional theory at the level of Perdew-Wang generalized-gradient approximation was applied to optimize PLA crystal unit cells. A comparison of energies in the various unit cells reveals that sc-form is the most energetically favorable form among the four PLA polymorphs. The order of thermodynamically relative stability is that sc-form is 0.3, 1.1, and 1.3 kcal/mol more stable than α-form, β-form, and γ-form, respectively (when using the ultrasoft pseudopotential and a plane-wave basis set with an energy cutoff of 380 eV) or 0.4, 1.1, and 1.3 kcal/mol more stable than α-form, β-form, and γ-form, respectively (when employing the density functional semi-core pseudopotentials and the double numerical plus polarization orbital basis set with a global orbital cutoff of 3.7 Å). In addition to the energetic properties, structural and electronic properties were calculated as well. The theoretical predicted stability rank is in agreement with some reported observations. Such as, sc-form has higher melting point and larger heat of fusion than those of α-form. The enhanced thermal stability of the sc-form compared to the other three homopolymer forms may be attributed to the unique intermolecular non-conventional hydrogen bonding C-H?O(C) network in the stereocomplex.     

A refined model for the active site within the NO decomposition catalyst, Cu-ZSM-5

Static atomistic simulation techniques have been employed to identify a model for the active site configuration and its location within the NO decomposition catalyst, Cu-ZSM-5. We propose that the active site comprises a copper pair, bridged by OH and forming a six membered ring, specifically, {-O-Cu(II)-OH-Cu(I)-O-Al-}, within the zeolite framework. The six-membered ring arises from the strong association of both of the copper species with a single aluminium in the zeolite framework and consequently the ring is strained, reflected in the low (3.1 Å) intercopper distance in the cluster. Indeed, this Cu-Cu distance compares well with the experimentally determined value of 3.0. In addition, it is expected that the strain in the cluster influences the activity of the cluster, which we suggest may be responsible for its unique activity for NO decomposition.     

A DFT study of methanol oxidation on Co3O4

By means of spin polarized density functional theory with the GGA + U framework, the reaction mechanism of CH₃OH oxidation on the Co₃O₄ (110)-B and (111)-B surfaces has been investigated. Adsorption situation and a part of reaction cycle for CH₃OH oxidation are clarified. Our results indicated that: i) U value can affect the calculated energetic result significantly; ii) CH₃OH can adsorb with surface lattice oxygen atom (O_2f/O_3f) to form CoO bond directly, and the adsorption of CH₃OH and its decomposition products on (110)-B is more stable than on (111)-B, which means CH₃OH prefers Co^3 + better than Co^2 +; iii) on the (110)-B surface, CH₃OH can form CO₂, H₂O and adsorbed H atom. But on the (111)-B surface, CH₃OH can just form formaldehyde (CH₂O) and adsorbed H atom, this means oxidative capacity of (110)-B (Co^3 +) is higher than (111)-B (Co^2 +). The possible reasons corresponding to the high oxidative of (110)-B come from both Co^3 + and O_2f: Co^3 + tends to bind adsorbed species for further decomposition and O_2f tends to bind more hydrogenation atom involved in methanol due to its low-coordinates number compared to that of O_3f.     

Pathways for steam reforming of dimethyl ether under cold plasma conditions: A DFT study

Density functional theory has been used to study the thermodynamics associated with the steam reforming of dimethyl ether (DME) under cold plasma conditions. The calculation showed that the only thermodynamic obstacle of the production of hydrogen, CO, dimethoxymethane (DMMT) and 1,2-dimethoxyethane (DMET) was the dissociation of DME and steam molecules, which was easy to be overcome under cold plasma conditions. The formation of hydrogen and CO was through a multi-step pathway via the methoxy radical conversion and dissociation of formaldehyde, while the recombination of H generated extra hydrogen. The syntheses of DMMT and DMET are from the recombination of and CH₃O, which could be primarily generated through DME dissociation or the reactions: H + CH₃OCH₃, OH + CH₃OCH₃, . The structure and electronic properties of DME anion were also studied in this work. Theoretical calculation showed that the DME anion was less stable than the neutral molecule. The route for the formation of and CH₃O from DME anion is thermodynamically favorable.     

A model of the electrochemical behaviour within a stress corrosion crack

A mathematical model of the electrochemical behaviour within a stress corrosion crack is proposed. Polarization field, crack geometry, surface condition inside the crack, electrochemical kinetics, solution properties and applied stress can be represented by the polarization potential and current, the electrochemical reactive equivalent resistance of the electrode, the change in electrolyte specific resistance and surface film equivalent resistance, respectively. The theoretical calculated results show that (i) when anodic polarization potential is applied, the change in the crack tip potential is small; (ii) when cathodic polarization potential is applied, the crack tip potential changes greatly with the applied potential; (iii) the longer the crack, the smaller the effect of the applied potential on the crack tip potential in both anodic polarization and cathodic polarization conditions. The calculated results are in good agreement with previous experimental results.Notation coordinate, from crack mouth (on the metal surface) to crack tip (cm) - y y = s _L L/(s ₀ – s _L) + L – , function of (cm) - y ₀ y ₀ = s _L L/(s ₀ – s _L) + L (cm) - V polarization potential (V) - galvanic potential of electrode (V) - ₁ galvanic potential of electrolyte (V) - t sample thickness (cm) - w sample width (cm) - S _L crack tip width (cm) - S _o crack mouth width (cm) - L crack length (cm) - s() crack width at position (cm) - _lo specific resistance of electrolyte, as a constant ( cm) - _s specific resistance of metal ( cm) - (, y) specific resistance of electrolyte, varies with potential and crack depth ( cm) - R _b (, y) electrochemical reactive equivalent resistance of electrode, varies with potential and crack depth () - R ₁ electrolyte resistance () - R _s metal resistance () - r(, y) surface film equivalent resistance, varies with potential and crack depth () - r _o surface film equivalent resistance, as a constant () - I _o total polarization current (A) - I net polarization current from integrating 0 to in Fig. 2 (A) - polarization overpotential (V) - _a anodic polarization overpotential (V) - _c cathodic polarization overpotential (V) - Euler's constant     

First-principles DFT study of SO2 and SO3 adsorption on 2PANI: a model for polyaniline response

Interaction of SO_x (x?=?2,3) molecules on active sites of dianiline (as a model for polyaniline, denoted here as 2PANI) was studied using density functional theory at the BLYP-D/6-31+G(d) level of theory. Natural population analysis was used to find out the charge distribution as well as the net transferred charge of SO_x upon adsorption on 2PANI and the result has been compared with Mulliken charge analysis to evaluate the sensing ability of 2PANI. The computed density of states point to the remarkable orbital hybridization between SO_x and 2PANI during the adsorption process. As a consequence, the results of UV–VIS confirm the sensing ability of 2PANI toward SO₂ and SO₃. Based on our results, it can be found that at proper configuration the SO₂ and SO₃ molecules can be adsorbed on 2PANI with adsorption energies (E_ads) of ?18.2 and ?62.9?kJ/mol (BSSE), respectively.     

Equilibrium mixture of the diisopropylbenzenes: a DFT study

The total energy and Gibbs free energy of diisopropylbenzene isomers were calculated by the DFT/B3PW91/6-31G** method. Comparison of the isomer populations based on the DFT calculated Gibbs free energies with the literature experimental concentrations of diisopropylbenzenes are in good agreement.     

A DFT study on the addition and abstraction reactions of thiourea with hydroxyl radical

The thiourea + ^? hydrogen atom transfer mechanism has been investigated theoretically for the first time. The objectives of the study OHhave been to elucidate the nature of the reaction species, energetic, geometric, electronic and reaction kinetic properties for the reaction. The study has been performed with the DFT/BHHLYP, DFT/ωB97X-D and DFT/M06-2X methods, by using the 6-311++G(3df,2p) basis set. The study has been performed in vacuo and in aqueous media. The results of the study indicate that the ^?OH addition mechanism is thermodynamically favored to the direct H-atom abstraction mechanism. The activation energy is dependent on the media; it is higher in water solution than in vacuo. The direct H-atom abstraction mechanism is kinetically favored with respect to the ^?OH addition mechanism in both media, suggesting that the reaction of thiourea with ^?OH most likely proceeds through this mechanism. In water solution, the estimated apparent rate constant is close to the experimentally determined value. The spin density distribution on the thiyl is delocalized throughout the S–C–N region. The bond dissociation enthalpy is overestimated, with respect to experimentally available data, but suggests that H-atom transfer is easier in non-polar medium than in polar medium.     

Study of CNx films on 316L stainless steel for orthodontic application

In order to improve the friction property and corrosion resistance of 316L stainless steel (316LSS) in orthodontic application, carbon nitride (CNx) films were synthesized by using IBAD technique at a set of assisted N ion beam currents. X-ray photoelectron spectroscopy and Raman spectroscopy were used to characterize the bonding state and the microstructure of the CNx films. Results of tribological tests indicated that the 316LSS coated by CNx films exhibited lower friction coefficients than the uncoated one both in air and in artificial saliva. The electrochemical tests in artificial saliva confirmed that the corrosion resistance of 316LSS was evidently improved after coated with CNx films.     

有机溶剂析盐法生产试剂氯化钾

进行了用丙酮结晶析出工业氯化钾饱和水溶液中的氯化钾的研究。丙酮能有效地从饱和溶液中分离出氯化钾 ,据此开发出一种生产试剂氯化钾的新工艺 ,该工艺与传统工艺相比 ,具有流程简单 ,操作条件宽松 ,能耗低等优点     

Kinetics of the catalytic destruction of cyanogen chloride

The catalytic destruction of cyanogen chloride (CNCI) in air has been investigated in a fixed-bed microreactor using a 2.15% Pt/α-alumina catalyst. If the feed stream contains water vapor, CNCl conversion as high as 98% can be achieved at 375°C and 170 000 cm³ h⁻¹ g⁻¹ space velocity. In contrast, the CNCl conversion in a dry inlet gas stream is 20% at 440°C and 46 000 cm³ h⁻¹ g⁻¹ space velocity. Water vapor in the feed stream significantly enhances the conversion of CNCl by providing an alternate hydrolysis pathway for destruction. It also promotes the complete conversion of CNCl to CO₂ and HCl with negligible selectivity to CO and Cl₂. The CNCl conversion decreases with increasing concentration in the feed stream. A kinetic model of the form r = kC_a/1(1 + K_pC_p) adequately represents the data in the presence of water vapor.     

Investigation of sulfur poisoning of CNx oxygen reduction catalysts for PEM fuel cells

The role of the transition metal used during the growth of non-noble metal electrochemical oxygen reduction CN_x catalysts was investigated through sulfur treatment, a well-known poison for transition metal-based catalysts. The intent of sulfur poisoning was to show the existence of an electrocatalytic active site in CN_x that did not depend on iron. The sulfur treatment was shown to be effective on a platinum catalyst, as seen by the decreasing onset potential. The same treatment, however, not only showed no negative effect on the CN_x catalyst, but enhanced its performance, as seen by the increase in the onset potential. This suggests that, if there are iron-based active sites in these catalysts, they are either sulfur tolerant or they do not participate in the electrocatalytic oxygen reduction. The deposition of sulfur onto CN_x catalyst was verified by temperature-programmed oxidation and X-ray photoelectron spectroscopy. Iron K-edge X-ray absorption near edge structural analysis of the CN_x catalyst suggested that the iron phase, which was primarily composed of nanometer-sized metallic particles, was unchanged by sulfur poisoning, suggesting that the residual iron left in these materials is not catalytically accessible.     

应用A/O法处理焦化酚氰废水

介绍了生物脱氮原理、A/O工艺流程及污泥驯化和运行管理。采用该技术处理蒸氨后高浓度废水 ,外排水指标除 COD稍高外 ,其余均可达到有关排放标准。     

A simplified model for heat transfer from a cylinder immersed within a packed bed

A model is presented for heat transfer from an immersed cylinder within a packed bed of particles to gas flowing through the bed parallel to the cylinder's axis.Simplifications in the model permit a closed form solution which agrees closely with the results of a previous numerical solution [1] when similar correlations for the physical mechanisms are employed. The results are shown to be sensitive to the values of the heat transfer coefficient at the cylinder wall and the gas velocity close to the wall.