A. Olivas

Evolution of crystalline phases in nickel-tungsten sulfide catalysts

Abstract Unsupported Ni–W sulfide catalysts were prepared employing ammonium thiotungstate complexes and nickel nitrate as metal-sulfide precursors. Structural characterization was carried out by XRD and HRTEM measurements. XRD patterns show crystallinity enhancement of WS 2 particles as the W content in the mixed catalysts was decreased. HRTEM demonstrates that WS 2 layers start to coat NiS particles when the amount of Ni was increased.

Solvothermal synthesis of nickel-tungsten sulfides for 2-propanol dehydration.

The bimetallic nickel-tungsten catalysts were prepared via solvothermal method. The X-ray Diffractometer (XRD) analysis revealed that the corresponding peaks at 14°, 34°, and 58° were for tungsten disulfide (WS2 ) hexagonal phase. The catalysts displayed different crystalline phase with nickel addition, and as an effect the WS2 surface area decreased from 74.7 to 2.0 m(2) g(--1) . In this sense, high-resolution transmission electron microscopy (HRTEM) showed the layers set in direction (002) with an onion-like morphology, and in the center of the particles there is a large amount of nickel contained with 6-8 layers covering it. The catalytic dehydration of 2-propanol was selective to propene in 100% at 250 °C for the sample with 0.7 of atomic ratio of Ni/Ni + W.

Study of the morphology of ZnS thin films deposited on different substrates via chemical bath deposition

In this work, the influence of substrate on the morphology of ZnS thin films by chemical bath deposition is studied. The materials used were zinc acetate, tri-sodium citrate, thiourea, and ammonium hydroxide/ammonium chloride solution. The growth of ZnS thin films on different substrates showed a large variation on the surface, presenting a poor growth on SiO2 and HfO2 substrates. The thin films on ITO substrate presented a uniform and compact growth without pinholes. The optical properties showed a transmittance of about 85% in the visible range of 300-800 nm with band gap of 3.7 eV.