Metal cerium oxide

In conclusion, there is overwhelming evidence for the beneficial effect of cerium oxide on the activity of the noble metal catalyst. However, the nature of the promoter effect of ceria is not fully understood. Most likely, the noble metal-cerium oxide interface is of crucial importance for some of the effects observed. More studies with model systems are needed for a better understanding of the promoter effects of ceria. 

Idriss, H. Ethanol reactions over the surfaces of noble metal/cerium oxide catalysts. Platinum... 

At the beginning of the twentieth century, the incandescent mantle, utilising the candoluminescence of a mixture of thorium (95% weight) and cerium oxides was developed. The pyrophoricity of rare-earth metals led to the invention of the lighter flint made through the alloying of iron and mischmetal. Since that time, numerous other appHcations have developed to coincide with the availabiUty of the rare-earth compounds on an industrial scale and having a controlled purity. 

Catalysts used for preparing amines from alcohols iaclude cobalt promoted with tirconium, lanthanum, cerium, or uranium (52) the metals and oxides of nickel, cobalt, and/or copper (53,54,56,60,61) metal oxides of antimony, tin, and manganese on alumina support (55) copper, nickel, and a metal belonging to the platinum group 8—10 (57) copper formate (58) nickel promoted with chromium and/or iron on alumina support (53,59) and cobalt, copper, and either iron, 2iac, or zirconium (62). 

In addition to platinum and related metals, the principal active component ia the multiflmctioaal systems is cerium oxide. Each catalytic coaverter coataias 50—100 g of finely divided ceria dispersed within the washcoat. Elucidatioa of the detailed behavior of cerium is difficult and compHcated by the presence of other additives, eg, lanthanum oxide, that perform related functions. Ceria acts as a stabilizer for the high surface area alumina, as a promoter of the water gas shift reaction, as an oxygen storage component, and as an enhancer of the NO reduction capability of rhodium. 

At a much earlier stage in the research and development cycle, fluidized-bed processes use porous sorbents containing copper oxide (82), cerium oxide (83), and other metal oxides (84). 

Fillers can also be used to promote or enhance the thermal stability of the silicone adhesive. Normal silicone systems can withstand exposure to temperatures of 200 C for long hours without degradation. However, in some applications the silicone must withstand exposure to temperatures of 280 C. This can be achieved by adding thermal stabilizers to the adhesive formulations. These are mainly composed of metal oxides such as iron oxide and cerium oxide, copper organic complexes, or carbon black. The mechanisms by which the thermal stabilization occurs are discussed in terms of radical chemistry. 

E. S. Shedd, J. D. Merchaw and T. A. Henrie, Continous Electrowinning of Cerium Metal from Cerium Oxides, U. S. Bureau of Mines, Rept. Invst. No. 6362,1964. 

Siriwardane, R.V., J.A. Poston, E.P Fisher, T.H. Lee, S.E. Dorris, and U. Balachandran, Characterization of ceramic-metal composite hydrogen separation membranes consisting of barium oxide, cerium oxide, yttrium oxide, and palladium, Appl. Surf. Sci., 217, 43-49, 2003. 

Izu, N. Murayama, N. Shin, W. Matsubara, I. Kanzaki, S. 2004. Resistive oxygen sensors using cerium oxide thin films prepared by metal organic chemical vapor deposition and sputtering. Jpn. J. Appl. Phys. 43 6920-6924. 

Catalyst systems for the WGS reaction that have recently received significant attention are the cerium oxides, mostly loaded with noble metals, especially platinum 42—46]. Jacobs et al. [44] even claim that it is probable that promoted ceria catalysts with the right development should realize higher CO conversions than the commercial Cu0-Zn0-Al203 catalysts. Ceria doped with transition metals such as Ni, Cu, Fe, and Co are also very interesting catalysts 37,43—471, especially the copper-ceria catalysts that have been found to perform excellently in the WGS reaction, as reported by Li et al. [37], They have found that the copper-ceria catalysts are more stable than other Cu-based LT WGS catalysts and at least as active as the precious metal-ceria catalysts. 

As a pure metal, cerium is unstable and will decompose rapidly in moist air. It also decomposes in hot water to form hydrogen. Its oxide compounds and halides are stable and have a number of uses. 

The compound cerium oxide (either Ce Oj or CeO ) is used to coat the inside of ovens because it was discovered that food cannot stick to oven walls that are coated with cerium oxide. Cerium compounds are used as electrodes in high-intensity lamps and film projectors used by the motion picture industry. Cerium is also used in the manufacturing and polishing of high-refraction lenses for cameras and telescopes and in the manufacture of incandescent lantern mantles. It additionally acts as a chemical reagent, a misch metal, and a chemical catalyst. Cerium halides are an important component of the textile and photographic industries, as an additive to other metals, and in automobile catalytic converters. Cerium is also used as an alloy to make special steel for jet engines, solid-state instruments, and rocket propellants. 

Lanthanide-containing porous materials have found many applications in various fields [20-22], They are known as active and selective catalysts for synthesis of higher hydrocarbons (mostly ethane and ethylene) from methane [23], which is of considerable importance for utilizing the reserves of natural gas around the World. Cerium oxide has been employed as a catalyst or as a structural promoter for supported metal oxide catalysts... 

Metal oxides have often been used as catalysts for the autoxidation of hydrocarbons.1 In many cases the metal probably dissolves in the reaction medium and catalysis involves homogeneous metal complexes. However, according to a recent report56 cerium oxide catalyzes the liquid phase oxidation of cyclohexanone in acetic acid (5-15 bar and 98-118°C) without dissolving in the reaction medium. 

Fig. 7.4 High-resolution transmission electron microscopy (TEM) image of a rhodium on a modified cerium oxide (Ceo.gTbo.202 x) after reduction, showing how the metal is almost epitaxially attached to the support, (a) TEM image (b,c) digital diffraction patterns obtained by Fourier transformation from the images (d) structure model ...

There have been a few studies on the surface oxidation of cerium. Oxidation of cerium has been studied by UV photoelectron spectroscopy [48] and XPS [49]. From these studies, the formation of Ce203 on the surface of the metal has been concluded along with evidence for... 

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