M. Avalos

Influence of preparation conditions on formation of crystalline phases of nickel sulfide

Abstract Nickel sulfide catalysts obtained by homogeneous precipitation were prepared by varying the homogenization time and the sulfiding temperature. The surface area with respect to preparation conditions was studied by the BET method. Structure characterization studies by X-ray diffraction showed the formation of two main crystalline phases (NiS 1.03 and NiS–millerite). Their appearance depends on preparation conditions. Formation of millerite or NiS 1.03 occurs at the constant sulfiding temperature, when time of homogenization of precursors increases.

Catalytic activity in the hydrocarbon conversion of systems containing platinum, nickel, iron, and zinc nanoparticles (communication 2)

The catalytic activity of metal-containing zeolites modified by nanosized Pt, Ni, Fe, and Zn powders was studied in the process of upgrading the petroleum straight-run gasoline fractions. It was found that the introduction of metal nanoparticles into the zeolite increases the catalyst activity and allows the desired product to be obtained at a lower processing temperature. An enhancement of the aromatization reactions of the hydrocarbon feedstock was revealed on the catalyst samples deactivated in the first reaction cycle and calcined in air.

Catalytic activity in hydrocarbon conversion of pentasil containing platinum, nickel, iron, or zinc nanoparticles

Catalyst samples containing nanosized Pt, Ni, Fe, or Zn powder were prepared on the basis of high-silica zeolite ZSM-5 by mechanical mixing. The structure and state of active centers of zeolite catalysts (freshly prepared or calcined after the reaction cycle of upgrading the petroleum straight-run gasoline fraction) were studied by means of the X-ray diffraction, UV spectroscopy, and X-ray photoelectron spectroscopy techniques. It was shown that the oxidized forms of the metals are practically absent from the freshly prepared zeolite samples. After the heat treatment of the catalysts in air, nanosized metal powders transform into oxides on the zeolite surface, with iron and nickel producing the greatest variety of oxidized forms.

Crystal chemistry of molybdenum phosphides from density functional theory calculations

Abstract The structures, bonding and relative thermodynamic stabilities of the crystalline molybdenum phosphides Mo 3 P, Mo 8 P 5 , Mo 4 P 3 , MoP, MoP 2 , MoP 4 , have been investigated by density functional theory calculations. The elastic stiffness coefficients for MoP and MoP 2 have been predicted.

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.

11-P-20 - Modification of mordenite and natural clinoptilolite by copper: role of drying temperature

Publisher Summary This chapter discusses the influence of pre-reduction heating treatment in air on the reducibility of copper supported on clinoptilolite and mordenite. After dehydration, the process of Cu-mordenite reduction is hindered and the formation of copper particles is suppressed. This result could be used for the stabilization of copper (Cu) inside the zeolite pores and the prevention of copper agglomeration on the external surface, which could lead to improved catalysts for de-NOx processes.

Influence of Preparation on the Morphology and Microstructure of Cobalt-Molybdenum Sulphides

Abstract Electron microscopy, X-ray diffraction and Auger spectroscopy studies were made on unsupported Co–Mo sulphides in order to elucidate the influence of preparation on the structural properties of these solids. The effect of varying the cobalt loading in two series of catalysts prepared by different methods was studied. The precipitation (HSP) and the impregnation (ITD) methods were used. X-ray and electron diffraction patterns showed that the crystallinity of Co9S8 in mixed sulphides depends strongly on the method of preparation. Scanning micrographs revealed differences in morphology for both methods, precipitated samples show irregular highly porous particles, whereas impregnated samples show well defined shapes for MoS2 particles and over them some aggregates as a function of the preparation method. The present results show that the final form of cobalt in mixed sulphides depends strongly on the way of preparation. The impregnation procedure allowed a good distribution of cobalt on the MoS2 surface mainly by forming a poorly crystalline form of Co9S8 and atomically dispersed cobalt.