DFT calculations on the catalytic oxidation of CO over Si-doped (6,0) boron nitride nanotubes

The oxidation of carbon monoxide (CO) is important for a series of technological and environmental applications. In this work, the catalytic oxidation of CO on Si-doped (6,0) boron nitride nanotubes (BNNTs) is investigated by using density functional theory calculations. Reaction barriers and corresponding thermodynamic parameters were calculated using the M06-2X, B3LYP and wB97XD density functionals with 6-31G* basis set. Our results indicate that a vacancy defect in BNNT strongly stabilizes the Si adatom and makes it more positively charged. This charging enhances the adsorption of reaction gases (O₂ and CO) and results in the change of the electronic structure properties of the tube. The calculated barrier of the reaction CO + O₂ → CO₂ + O_ads on Si-doped BNNTs following the Langmuir–Hinshelwood is lower than that on the traditional noble metal catalysts. The second step of the oxidation would be the Eley–Rideal reaction (CO + O_ads → CO₂) with an energy barrier of about 1.8 and 10.1 kcal/mol at M06-2X/6-31G* level. This suggests that the CO oxidation catalyzed by the Si-doped BNNTs is likely to occur at the room temperature. The results also demonstrate that the activation energies and thermodynamic quantities calculated by M06-2X, B3LYP and wB97XD functionals are consistent with each other.     

A DFT study on the healing of N‐vacancy defects in boron nitride nanosheets and nanotubes by a methylene molecule

In the present work, density functional theory calculations are used to investigate the healing mechanism of a N‐vacancy defect in boron nitride nanosheet (BNNS) or nanotube (BNNT) with a CH₂ molecule. The healing process starts with the chemisorption of CH₂ at the defect site, followed by its dehydrogenation over the surface. Next, a H₂ molecule is produced which can be easily released from the surface due to its small adsorption energy. For the dehydrogenation of CH₂ molecule over the defective BNNS or BNNT, the first C? H bond dissociation is the rate determining step. Our results indicate that the dehydrogenation of CH₂ over BNNS is both thermodynamically and kinetically more favorable than over BNNT. Besides, this study proposes a novel method for achieving C‐doped BNNSs and BNNTs. Given that the healing process proceeds without using a metal catalyst, therefore, no any purification is needed to remove the catalyst.     

Comments on “Delayed-state-feedback exponential stabilization for uncertain Markovian jump systems with mode-dependent time-varying state delays”

In this note some points for paper [Huabin Chen, Chuanxi Zhu, Peng Hu, Yong Zhang, Delayed-state-feedback exponential stabilization for uncertain Markovian jump systems with mode-dependent time-varying state delays, Nonlinear Dyn. (2012), doi:10.1007/s11071-012-0324-3] are presented.     

Synthesis and characterization of Co(II), Ni(II), Zn(II) and Cu(II) complexes with a new tetraazamacrocyclic Schiff base ligand containing a piperazine moiety: X-ray crystal structure determination of the Co(II) complex

Two macrocyclic Schiff base ligands, L¹ [1+1] and L² [2+2], have been obtained in a one-pot cyclocondensation of 1,4-bis(2-formylphenyl)piperazine and 1,3-diaminopropane. Unfortunately, because of the low solubility of both ligands, their separation was unsuccessful. In the direct reaction of these mixed ligands (L¹ and L²) and the appropriate metal ions only [CoL¹(NO₃)]ClO₄, [NiL¹](ClO₄)₂, [CuL¹](ClO₄)₂ and [ZnL¹(NO₃)]ClO₄ complexes have been isolated. All the complexes were characterized by elemental analyses, IR, FAB-MS, conductivity measurements and in the case of the [ZnL¹(NO₃)]ClO₄ complex with NMR spectroscopy.     

Flow characteristics in a model of a left ventricle in the presence of a dysfunctional mitral mechanical heart valve

Journal of Visualization -     

Optically nonlinear phonon-polariton modes in a three-layered structure

A theory is presented for the propagation of phonon-polariton modes arising when phonons are coupled to electromagnetic waves in multilayered structures. A multi-layered structure consists of a thin film surrounded symmetrically by a bounding media. Numerical calculations are given for s-polarized phonon-polariton modes in the case where the bounding media are assumed to be semi-infinite layers with nonlinear dielectric functions of ionic crystal type supporting optical phonon modes and the thin film is characterized by a Kerr-type nonlinear dielectric function. The phonon-polaritons were found to have distinct branches characteristic of optical phonons and showing features that are different from those of plasmon-polaritons [S. Baher, M.G. Cottam, Surf. Rev. Lett. 10 (2003) 13]. The parameters that modify the modes are the in-plane wave vector, the thickness of the film, the phonon frequency and the nonlinearity of each layer. It was found that by increasing the film thickness and nonlinearity coefficient, the curves move to the left and the number of the branches increases without changing the pattern of the curves.     

Selective oxidation of sulfurs and oxidation desulfurization of model oil by 12-tungstophosphoric acid on cobalt-ferrite nanoparticles as magnetically recoverable catalyst

Silica-coated CoFe2O4 nanoparticles were prepared and used as a support for the immobilization of 12-tungstophosphoric acid, to produce a new magnetically separable catalyst. This catalyst was characterized using X-ray diffraction, wavelength-dispersive X-ray spectroscopy, Fourier-transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, laser par-ticle size analysis, and vibrating sample magnetometry. The catalyst showed high activity in the selective oxidation of thioethers and thiophenes to the corresponding sulfones under mild condi-tions. The catalytic activity of the nanocatalyst in the oxidative desulfurization of model oil was investigated. The effect of nitrogen-containing compounds on sulfur removal from the model oil was also evaluated. The catalyst showed high activity in the oxidative desulfurization of diesel. The cata-lyst can be readily isolated from the oxidation system using an external magnet and no obvious loss of activity was observed when the catalyst was reused in four consecutive runs.     

Theoretical insight to the complexation of some transition metals with cryptand

The most practicable complexes formed between Cryptand[2.2.2] and hydrated Mn(II), Fe(II), Co(II), Ni(II), Cu(II), and Zn(II) cations (denoted as [ML]⁺²) were modeled using computational chemistry methods. The energies of complexation reactions were calculated in both gas phase and solution at B3LYP/6-31+G(d) and B3LYP/6-311++G(3df,2pd) levels of theory. The accuracy of selected computational methods was confirmed with comparison between available X-ray data and computational results. The results suggested that [CuL]⁺² and [CoL]⁺² structures could be the most and the least stable systems, respectively. The nature of metal-ligand interactions based on quantum theory of atoms in molecule (QTAIM) was discussed for all the complexes. This analysis confirmed the ionic nature of metal-ligand interactions due to electron density values for M-O bonds and M-N interactions. Natural bond orbital (NBO) and natural energy decomposition analysis (NEDA) were utilized to explain more details of interaction between divalent cations and donor atoms of the ligand.