Martin Schmal

Quantitative XPS analysis of silica-supported Cu–Co oxides

Abstract Copper–cobalt oxides with Cu/Co=5:5, 15:15 and 35:35 bulk ratio have been prepared by deposition–precipitation method at constant pH from copper and cobalt nitrate solutions. Different oxides were obtained by decomposition of the precursors at 673 K for 7 h in air and analyzed by X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). XRD data showed the formation of different oxide phases; for the bulk atomic ratio of 15Cu:15Co, a phase containing Cu and Co with spinel-like structure was observed, while the other bimetallic oxides presented CuO and Co3O4 as distinct phases. The XPS qualitative analysis has shown that all samples exhibited Cu2+ and Co3+ species at the surface. The Cu–Co spinel presented a displacement in Cu 2p binding energy value. A mathematical model was proposed from relative intensity ratios, which allowed the determination of the oxide particle thickness and the fraction of coverage at the support. This model described accurately the system and showed that cobalt improved the copper dispersion.

The nickel–niobia–silica interactions at low nickel contents

Abstract Nickel was impregnated in two Nb 2 O 5 /SiO 2 samples. The first one contained small crystallites of niobia dispersed over silica and the second one a niobia monolayer distributed quite uniformly over the silica substrate. These systems were submitted to different treatments (calcination and water vapor) in order to obtain different interactions between the nickel and niobia. A preferential interaction of the nickel with niobia was observed in both niobia–silica samples. The hydrogenation of benzene and dehydrogenation of cyclohexane were used to characterize the reduced surface nickel. Suppression in the catalytic activity was observed due to a strong metal-support interaction (SMSI) and nickel niobate formation. The extension of SMSI and nickel niobate formation depend on the niobia–silica interactions, which are a function of sample preparation and treatment.

Cyclohexane as a Probe to Nickel Vanadium Interaction in FCC Catalysts

Abstract Nickel and vanadium were responsible for a great number of deactivation problems in the FCC. To understand their mutual influences, the metals were introduced by incipient wetness impregnation of organometallic compounds onto a highly dealuminated zeolite that had a constant lattice similar to the equilibrium FCC catalyst. Catalyst tests, TPR, DRS and X-ray diffraction were used to characterize the samples. After calcination, the acid sites of the zeolite were poisoned by vanadium without damage to the Crystallinity. Water vapor and high temperature treatment on vanadium/zeolite samples leads to a severe damage of the zeolite framework. The presence of nickel slightly attenuated this problem. The amount of benzene formed was affected by the Ni/V ratio.

Heterogeneous Catalysis and its Industrial Applications

The importance of catalysis is due to the large number of applications in catalytic processes, particularly in the chemical and petrochemical industry, in power generation, the gas and water pollution to preserve the environment and the development of new materials. This book aims to present the fundamentals of catalysis and applications illustrated with experiments performed in our laboratory, trying to understand why select the catalysts and processes.

Oxidative coupling of methane on Ce/Na/CaO catalysts

Oxidative coupling of methane was investigated on Na/CaO and Ce/Na/CaO catalysts with different sodium and cerium contents. The reaction was carried out in a micro fixed-bed flow reactor operating at atmospheric pressure, at 700 and 750°C and molar ratio feed of CH4 : O2 : N2 = 50 : 10 : 40. Catalysts were compared at isoconversion and were characterized by BET, XRD and XPS. The addition of cerium to Na/CaO catalyst increased the specific activity by a factor of eight. These catalytic and characterization results were related to the presence not only of Na+O- active sites, formed by the introduction of Na+ in the CaO lattice, but also to peroxide active sites. A mechanism is proposed to explain the role of cerium in increasing the rate of the regeneration step of the Os– and Na2O2 sites.

X-Ray Photoelectron Spectroscopy (ESCA: XPS/ISS)

The photoemission spectroscopy is one of the most important techniques for the study of surfaces and interfaces, enabling you to determine the oxidation state, the dispersion of the phases and the dependence of the atomic concentration with depth. It allows determining the chemical state and several other surface informations.

Kinetics and Mechanisms

The classical kinetics uses specific models for determining the kinetic parameters, the rate constants and reaction orders. We will present some specific cases in order to determine quantitatively the kinetic parameters of the reaction rates and suggest mechanisms, based on the identification of intermediate species.

Textural and Thermochemical Characterizations

Textural and thermo-chemical methods of characterizations of solid materials, metals and oxides.

Structural Analyses: X-ray Diffraction

Structural analyses of materials are presented using x-ray diffraction techniques. Rietveld method was applied for determining cell parameters.

Spectroscopy in the Infrared Region

Infrared is one important spectroscopic tool for elucidating molecular structure and qualitatively and quantitatively determining organic and inorganic compounds. Among these, spectroscopy in the infrared region stands out for analyses of molecules absorbed in a surface. Diffuse reflectance measures the energy spread diffusely after interaction with electromagnetic radiation in the infrared region with a discontinuous matrix.