Advances in the development of novel cobalt Fischer-Tropsch catalysts for synthesis of long-chain hydrocarbons and clean fuels.

An overview is given on the ongoing activities in the area of the decomposition of nitrous oxide, N2O, over solid catalysts. These catalysts include metals, pure and mixed oxides, supported as well as unsupported, and zeolitic systems. The review covers aspects of the reaction mechanism and kinetics, focusing on the role of surface oxygen, the inhibition by molecular oxygen, water and other species, poisoning phenomena and practical developments.

Heterogeneous catalytic decomposition of nitrous oxide

Copper-based catalysts are active in a wide range reactions of transformation of nitrogen oxides and represent an useful model system to better understand the fundamental aspects of the chemistry and mechanism of reaction of catalytic transformation of these pollutants. After an introduction on the reactivity of copper-based catalysts (supported and unsupported copper oxide, Cu-zeolites, cuprates and other copper compounds) in various reactions of conversion of nitrogen oxides, four main sub-topics are discussed in detail: (i) nature of copper species, (ii) chemisorption and surface transformations of NO, (iii) relationship between copper species and activity in the conversion of nitrogen oxides and (iv) mechanism of reduction of nitrogen oxides to N 2 . Five reactions of transformation of nitrogen oxides are discussed in detail: (i) decomposition of NO, (ii) reduction of NO with ammonia in the presence or not of oxygen, (iii) reduction of NO with hydrocarbons in the presence of oxygen, (iv) reduction of NO with CO and (v) decomposition of N 2 O. The mechanism of reduction of nitrite and N 2 O by copper enzymes is also discussed, with a view to provide some useful insights on the chemistry of transformation. In this review particular attention is directed towards controversial points in the literature, underestimated questions, and hypothesis and theories which do not allow interpretation of all sets of experimental data. Discussion is also focused on the presence of multiple and competitive pathways of transformation, the relative roles of which depend on reaction conditions.

Nature of active species in copper-based catalysts and their chemistry of transformation of nitrogen oxides

Copper-Zinc Oxide-Alumina Methanol Catalysts Revisited

Bright blue CoAl2O4 particles were prepared by the sol−gel and citrate−gel methods using aluminum sec-butoxide, cobalt salts, and citric acid as oxides precursors. Both methods start from sols of the precursor alkoxides and salts, and involve formation of homogeneous solid intermediates, reducing atomic diffusion processes during thermal treatment. This important feature results in a substantial lowering of the time and temperature needed for the formation of the desired compounds. The stages of the formation of CoAl2O4, as well as the characterization of the resulting compounds were done using XRD, FTIR, UV−VIS, SEM, and TGA/DTA techniques. The structure, coloration, particle size, and temperature of formation of the resulting CoAl2O4 phases were found to depend on the precursors and methods used for preparation and the calcination temperature. The lowest temperature for preparation of the blue cobalt aluminate of about 700 °C was obtained using the citrate−gel method. This temperature is much lower than...

Blue CoAl2O4 particles prepared by the sol-gel and citrate-gel methods

Catalytic behavior and surface chemistry of copper/alumina catalysts for isopropanol decomposition

The cation distribution in CoAl2O4 and in several CoχMg1–χAl2O4 solid solutions with χ ranging from 0.05 to 0.5 has been studied by magnetic susceptibility, reflectance spectroscopy, lattice parameter variation and analysis of some X-ray reflections whose intensities are particularly sensitive to variation in cation positions.The results show that all specimens have the cobalt ions in a predominantly tetrahedral distribution and that there is a change towards a random cation distribution when the preparation temperature is increased from 1073 to 1473 K. The fraction of Co2+ ions in tetrahedral sites, α, is equal to 0.82 and 0.77 for the CoAl2O4 spinel prepared at 1073 and 1473 K, respectively.The X-ray results show, moreover, that α does not vary significantly with composition for χ varying from 1.0 to 0.1. For the most dilute cobalt solid solution (χ= 0.05), however, the value of α is lower; this trend is observed in both series of specimens prepared at different temperatures and may be explained in terms of anion–anion contact effects.

Structure and catalytic activity of CoχMg1–χAl2O4 spinel solid solutions. Part 1.—Cation distribution of Co2+ ions

The catalytic decomposition of N2O was studied on spinel catalysts of general formula CoxMg1–xAl2O4(x= 0 → 1). The bulk distribution of Co2+ ions is predominantly tetrahedral with a small fraction of Co2+ in octahedral symmetry. It is shown that the octahedral coordination of Co2+ allows a catalytic activity larger than that attributable to tetrahedral coordination. The results also indicate that the surface Co2+ distribution is different from that found in the bulk by X-rays.The influence of the matrix on the activity is discussed in terms of surface—oxygen bond strength and a comparison is made with MgO- and ZnO- based catalysts.

Structure and catalytic activity of CoxMg1–xAl2O4 spinel solid solutions. Part 2.—Decomposition of N2O

The catalytic properties of copper oxides (CuO and Cu20), and CuO—MgO and CuO—ZnO solid solutions, have been investigated. Structural studies (X-ray diffraction, \"LTV. and VIS. reflectance spectroscopy and magnetic susceptibility measurements) allow the systems to be fully characterized. Their catalytic activity towards the decomposition of N20 has been tested in the range 250° to 500 °C. It was thus possible to confirm that Cu20 is very active for this reaction, whereas CuO has only very low activity. For the CuO—MgO and CuO—ZnO solid solutions, it has been shown that, under repeated vacuum conditioning treatments and catalytic experiments, a segregation of Cu20 occurs. This species is responsible for the catalytic activity. The CuO—ZnO specimens are more active than the CuO—MgO ones because of a greater Cu20 segregation in the former system. The role of the matrix in the segregation process is discussed.

The Catalytic Activity of Copper Ions in Copper Oxides and in their Solid Solutions with ZnO and MgO for the Decomposition of N2O

Es wurde die Adsorption von O2 und C3H6 an den Wolfram-Oxiden WO3, WC\"2,96, WO2.90, W02,72 und WO2 untersucht. Die Ergebnisse werden in Bezug zu früheren katalytischen Untersuchungen (N20-Zerfall und CsHe-Oxydation) erläutert. Es wird die besondere Rolle der strukturellen Anordnung der reduzierten Phasen bei katalysierten Umsetzungen mit Beteiligung von Sauerstoff gezeigt. Introduction The decomposition of N2O and the oxidation of propene over

F. Pepe

Papers

Catalytic behavior and surface chemistry of copper/alumina catalysts for isopropanol decomposition

Structure and catalytic activity of CoχMg1–χAl2O4 spinel solid solutions. Part 1.—Cation distribution of Co2+ ions

Structure and catalytic activity of CoxMg1–xAl2O4 spinel solid solutions. Part 2.—Decomposition of N2O

The Catalytic Activity of Copper Ions in Copper Oxides and in their Solid Solutions with ZnO and MgO for the Decomposition of N2O

Adsorption of Oxygen and Propene over a Series of Tungsten Oxides