Mixed Oxides Of Co Research Articles

Synthesis and characterisation of mixed oxides of Co–Ni catalyst and its application in microwave mediated synthesis of Benzo[b]Pyrans

We present an easy and sustainable procedure for the productive preparation of tetrahydrobenzo[b]pyran derivatives by means of many compounds condensation of dimedon, malononitrile and several aromatic aldehydes utilizing mixed bimetallic oxides of Co–Ni as a catalyst under microwave irradiation. Present protocol involves green synthesis of mixed Co–Ni oxide catalyst using milky latex of Euphorbia neriifolia. The prepared mixed Co and Ni oxide was analyzed by X-ray diffraction (XRD), Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), Fourier Transform Infra-Red Spectroscopy (FT-IR), Energy Dispersive X-ray Analysis (EDAX), X-ray Photoelectron Spectroscopy (XPS) & Brunauer-Emmett- Teller Analysis (BET). This green approach's significance is demonstrated by its one-pot synthesis, convenient without use of solvent shows good isolated yields. Multiple analytical techniques such as Fourier transform infrared spectroscopy (FT-IR), 1H and 13C nuclear magnetic resonance (NMR) spectroscopy are utilized to derive the structural properties. The mixed metal oxides of Co and Ni was found to be catalytically active and can be reused 12 times without significant loss of catalytic activity.

COMPARISON OF ELECTROCATALYTIC SITES DENSITY ON ELECTRODES WITH Co<sub>3</sub>O<sub>4</sub> AND NiCo<sub>2</sub>O<sub>4</sub> COATINGS

The paper compares catalytic properties of spinel mixed oxides of Co 3 O 4 and NiCo 2 O 4 , that we synthesized, as possible catalysts for the oxygen reduction reaction in an alkaline medium. This reaction is one of the most important in the development of alternative energy sources with high specific characteristics – metal-air batteries and fuel cells. One of the reagents in such systems is oxygen; another necessary component can be a metal (Zn, Li, etc.) or hydrogen. We have employed the method of comparing catalytic activity for catalysts deposited on flat electrodes and have tried to achieve the sufficient adhesion in order to use the samples as electrodes. The Co3O4 catalyst was obtained on the substrate by hydrothermal method from a solution containing 0.1 M Co(NO 3 ) 2 and 0.4 M urea. The synthesis of NiCo 2 O 4 was carried out electrochemically from a solution containing 0.01 M Ni(NO 3 ) 2 and 0.02 M Co(NO 3 ) 2 . Sample characterization was carried out with X-ray analysis; electrochemical characteristics were obtained using cyclic voltammetry in 1 M NaOH solution. The paper finds out that catalytically active sites are formed on the electrode surface with a layer of the corresponding oxide during the cathodic polarization. Formation of one center during the electrode reaction corresponds to a twoelectron transfer. Total number of the active sites can be determined from the amount of electricity. Surface coverage was determined from the amount of electricity as a function of the potential calculated from the cathodic branch of the voltammogram curve. We carried out the calculation by the method of numerical integration using the trapezoidal rule in the Excel package. Based on the calculations performed, the form and parameters of the isotherm of the surface filling with active sites as a function of the electrode potential were established. The filling of the surface with active sites is shown for the first time to take place in accordance with the Frumkin–Temkin isotherm. We calculated the isotherm parameters, the density of the sites on the surface, and the effective distance between them. Most centers were obtained for an electrode with a layer of NiCo 2 O 4 – 2.27∙10 17 cm -2 . The original technique is of interest for comparing the catalytic activity of electrodes from various materials.

Combustion synthesis of Co-Cu-Mn oxides deploying different fuels

Ternary spinel-like oxides such as CuFeMnO4, CoCuMnOxand CuCr2O4 are attractive materials due to their absorbent properties when used as pigments for selective surfaces thus improving solar heaters efficiency. These materials are obtained through sol-gel and sol-gel-combustion methods. This work proposes the synthesis of mixed oxides of Co, Cu and Mn by means of original one-step stoichiometric combustion methods starting from Mn(NO3)2,Co(NO3)26H2O, Cu(NO3)23H2O and Aspartic acid (Asp) or Lysine( Lys) as fuels. The resulting ashes after the combustion were calcined at 500 °C. The obtained ashes and the calcined powders were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), and by Brunauer-Emmett-Teller method (BET), and TG-DTA analysis. In calcined powders obtained with Lys (CoCuMnOx-Lys), the phase corresponding to CoCuMnOx and others segregated phases were identified. However, in calcined powders obtained with Asp (CoCuMnOx-Asp) only the phase corresponding to CoCuMnOxwas identified. The sample CoCuMnOx-Lys presented an average crystallite size of 44 nm and a specific surface area of 23 m2/g while in CoCuMnOx-Asp, 54 nm and 13 m2/g values were obtained throughout FT-IR vibrational modes associated with spinel metallic oxides for both calcined powders (Asp and Lys) were observed. Additionally, by means of TEM, polyhedral particles with an average size of 20 to 100 nm were observed. In particular, it was determined in CoCuMnOx-Lys an average size of 44nm. According to the different fuels used (Asp and Lys), an evident variation in the obtained phases was observed. However, it was not obtained any difference in crystallite size and specific area surface values. It is of considerable importance the study of further syntheses processes to verify this trend.

Investigation of the mechanisms of Type-II hot corrosion of superalloy CMSX-4

A microstructural investigation of Type-II hot corrosion was carried out on a single crystal Ni-based superalloy (CMSX-4) pre-coated with Na2SO4 at 700°C in a flowing O2–SO2–SO3 atmosphere. Corrosion occurred by rapid dissolution of the alloy by molten sulfate eutectics, forming an outer layer rich in Co and Ni and an inner layer rich in Cr and Al. The outer layer transformed into mixed oxides of Co and Ni, with concurrent evolution of the continuous S-rich inner layer. A multicomponent analysis provides insight into diffusional interactions among Co, Ni, and S. Crystal orientation and microstructure effects were also studied.

Oxygen evolution reaction on Ni-substituted Co 3O 4 nanowire array electrodes

Nanowire arrays of mixed oxides of Co and Ni freely standing on Ni foam are prepared by a template-free growth method. The effects of Ni content on the morphology, structure and catalyst performance for oxygen evolution reaction are investigated by scanning electron microscopy, X-ray diffraction spectroscopy and electrochemical techniques including cyclic voltammetry, chronopotentiometry and electrochemical impedance spectroscopy. A transformation from nanowire arrays to nanoplate arrays is found with the increase of the atomic ratio of Ni to Co in the preparation solution. The Ni xCo 3−xO 4 electrode obtained at 1:1 of Ni:Co in the preparation solution exhibits nanowire array structure and has better catalytic performance for oxygen evolution reaction than other Ni xCo 3−xO 4 and Co 3O 4 electrodes. The catalytic activities of the Ni xCo 3−xO 4 and Co 3O 4 electrodes are correlated with their surface roughness. Superior stability of the Ni xCo 3−xO 4 nanowire array electrode is demonstrated by a chronopotentiometric test. The reaction orders with respect to OH − on the Ni xCo 3−xO 4 electrode are close to 2 and 1 at low and high overpotentials, respectively.