Carbon Microsphere-Supported Metallic Nickel Nanoparticles as Novel Heterogeneous Catalysts and Their Application for the Reduction of Nitrophenol

Nickel nanoparticles are gaining increasing attention in catalysis due to their versatile catalytic action. A novel, low-cost and facile method was developed in this work to synthesize carbon microsphere-supported metallic nickel nanoparticles (Ni-NP/C) for heterogeneous catalysis. The synthesis was based on carbonizing a polystyrene-based cation exchange resin loaded with nickel ions at temperatures between 500 and 1000 °C. The decomposition of the nickel-organic framework resulted in both Ni-NP and carbon microsphere formation. The phase composition, morphology and surface area of these Ni-NP/C microspheres were characterized by powder X-ray diffraction, Raman spectroscopy, scanning electron microscopy and BET analysis. Elemental nickel was found to be the only metal containing phase; fcc-Ni coexisted with hcp-Ni at carbonization temperatures between 500 and 700 °C, and fcc-Ni was the only metallic phase at 800–1000 °C. Graphitization and carbon nanotube formation were observed at high temperatures. The catalytic activity of Ni-NP/C was tested in the reduction of 4-nitrophenol to 4-aminophenol by sodium borohydride, and Ni-NP/C was proved to be an efficient catalyst in this reaction. The relatively easy and scalable synthetic method, as well as the easy separation and catalytic activity of Ni-NP/C, provide a viable alternative to existing nickel nanocatalysts in future applications.     

Generation and Spectroscopic Identification of ClCNS,ClNCS and NCCNS

The photolysis of four chloro‐substituted thiadiazoles (3,4‐dichloro‐, 3‐chloro‐ and 3‐chloro‐4‐fluoro‐1,2,5‐thiadiazole; 3,5‐dichloro‐1,2,4‐thiadiazole) and 3,4‐dicyano‐1,2,5‐thiadiazole was investigated in inert solid‐argon matrices at cryogenic temperatures by means of UV irradiation at selected wavelengths of 254 and 280 nm. The photolysis products were identified by mid‐IR and UV spectroscopy. Evidence for the existence of three novel pseudohalides, namely, chloronitrile sulfide (ClCNS), chlorine isothiocyanate (ClNCS) and cyanogen N‐sulfide (NCCNS), was provided by direct spectroscopic methods supported by quantum chemical calculations. Ground‐state geometries, vibrational frequencies, IR intensities, and UV excitation energies of ClCNS, ClNCS and NCCNS were obtained from calculations using the B3LYP, CCSD(T) and SAC‐CI methods and the aug‐cc‐pV(T+d)Z basis set.     

Generation and spectroscopic identification of selenofulminic acid and its methyl and cyano derivatives (XCNSe, X=H, CH3, NC)

Evidence for the existence of nitrile selenides, potential 1,3-dipolarophiles in cycloaddition reactions, has been provided by direct spectroscopic methods. The parent nitrile selenide, selenofulminic acid (HCNSe), and its methyl and cyano derivatives have been photolytically generated in an inert solid argon matrix from 1,2,5-selenadiazoles by 280, 254, and 313 nm UV irradiation, respectively, and studied by ultraviolet spectroscopy and mid-infrared spectroscopy. Ground-state geometries have been obtained from quantum-chemical calculations at the CCSD(T)/aug-cc-pVTZ level. Nitrile selenides are predicted to be linear with a relatively weak N-Se bond.     

On the convergence and divergence of Bairstow's method

Summary Necessary and sufficient condition of algebraic character is given for the invertibility of the Jacobian matrix in Bairstow's method. This leads to a sufficient condition for local quadratic convergence. Results also yield the rank of the Jacobian, when it is singular. In the second part of the paper we give several examples for two step cyclization and more complicated kind of divergence. Some of the polynomials in divergence examples are proved to be irreducible over the field of rational numbers.     

First Isolation and Spectroscopic Observation of Thiofulminic acid (HCNS)

For the first time : Thiofulminic acid (HCNS), the parent member of the nitrile sulfide family of reactive intermediates and potential interstellar species, was produced and characterized by IR spectroscopy for the first time. HCNS was generated in cryogenic matrices by 254 nm UV irradiation of 1,2,5‐thiadiazole (see figure).

     

On a Toeplitz Representation of the H1/2 Norm

Some representations of the H1/2 norm are used as Schur complement preconditioner in PCG based domain decomposition algorithms for elliptic problems. These norm representations are efficient preconditioners but the corresponding matrices are dense, so they need FFT algorithm for matrix-vector multiplications. Here we give a new matrix representation of this norm by a special Toeplitz matrix. It contains only O(log(n)) different entries at each row, where n is the number of rows and so a matrix-vector computation can be done by O(nlog(n)) arithmetic operation without using FFT algorithm. The special properties of this matrix assure that it can be used as preconditioner. This is proved by estimating spectral equivalence constants and this fact has also been verified by numerical tests.