Lanthanum cerium oxides

Y. Wang, S. Lianga, A. Caoa, R. L. Thompson, G. Vesera, Au-mixed lanthanum/cerium oxide catalysts for water gas shift, Appl. Catal. B Environ. 99 (2010) 89-95. 

Praseodymium is soft, silvery, malleable, and ductile. It is somewhat more resistant to corrosion in air than europium, lanthanum, cerium, or neodymium, but it does develop a green oxide coating that spalls off when exposed to air. As with other rare-earth metals, it should be kept under a light mineral oil or sealed in plastic. 

The lanthanum phosphate phosphor is usually prepared by starting with a highly purified coprecipitated oxide of lanthanum, cerium, and terbium blended with a slight excess of the stoichiometric amount of diammonium acid phosphate. Unlike the case of the aluminate phosphor, firing is carried out in an only slightly reducing or a neutral atmosphere of nitrogen at a temperature 1000° C. Also this phosphor is typically made with the addition of a flux,... 

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). 

Sihca is reduced to siUcon at 1300—1400°C by hydrogen, carbon, and a variety of metallic elements. Gaseous siUcon monoxide is also formed. At pressures of >40 MPa (400 atm), in the presence of aluminum and aluminum haUdes, siUca can be converted to silane in high yields by reaction with hydrogen (15). SiUcon itself is not hydrogenated under these conditions. The formation of siUcon by reduction of siUca with carbon is important in the technical preparation of the element and its alloys and in the preparation of siUcon carbide in the electric furnace. Reduction with lithium and sodium occurs at 200—250°C, with the formation of metal oxide and siUcate. At 800—900°C, siUca is reduced by calcium, magnesium, and aluminum. Other metals reported to reduce siUca to the element include manganese, iron, niobium, uranium, lanthanum, cerium, and neodymium (16). 

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. 

Lanthanum has been used extensively in camera lenses to give high refractive indices with low dispersion. Cerium oxide absorbs UV light strongly and hence prevents degradation of pigments. 

In Figure 8 we have plotted the lanthanum oxide, cerium oxide, and thorium oxide concentrations for sherds excavated in the Dominican Republic and Venezuela and sherds from the Metro excavations using a computer system developed for this purpose at Brookhaven National Laboratory (8). On the basis of these three oxides there is a distinct separation between the sherds from the Dominican Republic and Venezuela and those from Mexico City. Unlike the sherds from the Dominican Republic and Venezuela, the sherds from Mexico City appear not to have originated in Spain, at least at that specific source. There is further evidence of this distinction between the two sets of sherds. X-ray diffraction analysis of the samples from Jerez and from the New World showed that the sherds from Jerez, the Dominican Republic, and Venezuela had intense quartz peaks whereas the sherds from Mexico City did not. This constitutes additional evidence that the majolica from Mexico City came from a different source than the majolica from the Caribbean sites. 

Rare earth nitrates can be prepared using nitric acid to react with a corresponding oxide, hydroxide, carbonate or metal. These nitrates dissolve easily in polar solvents such as water, alcohols, esters or nitriles. They are unstable to heat as the decomposition temperature for the nitrates of scandium, yttrium, lanthanum, cerium, praseodymium, neodymium, and samarium are 510,480, 780,450, 505, 830, and 750 °C, respectively. 

Fission products that are compatible with the uraninite crystal stmcture—the REE, yttrium, neodymium, and zirconium—were largely retained in the uraninite core, the reactor clays, minor phosphate phases, and uranium and zirconium silicate phases (Gauthier-Lafaye et ai, 1996). Lighter REE—lanthanum, cerium, and praseodymium—were partially lost from the reactor. Einally, molybdenum, technetium, mthe-nium, rhodium, and other metallic elements were retained in the metal/metal oxide inclusions and arsenide/sulfide inclusions in the core, and in the reactor clays (Hidaka et ai, 1993 Jensen and Ewing, 2001). 

Chemicae Eormulas Common compounds o Cerium oxide CeiOs o Gadolinium oxide Gd203 o Lanthanum oxide LaiOs o Yttrium oxide Y2O3 o Cerium nitrate Ce(N03)3 o Cerium chloride CeCls... 

Mesoporous yttrium zirconium oxide or mesoporous cerium oxide anodes and a mesoporous lanthanum strontium manganate cathode constructed from nanocrystallites of these materials organized by a templating mesophase can be used in solid-oxide fuel cells. Mesoporous TiCU has a potential application in dye-sensitized solar cells. 

The results in Table 2 show that these catalysts are active for methanol synthesis. It was shown in the patent that they are also highly selective with the non-methanol organics content of the product being less than 1 wt %. The results in Table 2 show that the addition of Al to the alloys results in increased activity and life. They also suggest that cerium is preferred to lanthanum as the rare earth metal. After reaction the catalysts were examined and were found to consist of finely dispersed metallic copper in cerium oxide. As such they are similar to those produced from Cu-Th alloys (refs. 17,19). 

In the case of cerium exchanged zeolites, the ionic exchanges were carried out under nitrogen, in order to avoid the oxidation of cerium (III) ions. Part of the cerium (III) exchanged zeolite was calcined under oxygen for 6 hours at 540°C in order to convert cerium (III) to cerium (IV) ions. Lanthanum-cerium exchanged zeolites were prepared with the following composition 75% La, 25% Ce 50% La, 50% Ce and 25% La, 75% Ce. 

A key was the development of more thermally stable forms of cerium oxide. Unstabilized cerium oxide degrades rapidly at exhaust temperatures in excess of 800° C, and this degradation significantly reduces the efficiency of the catalyst for NO-N02 reduction. Greater thermal stability was achieved by forming solid solutions of stabilizers such as zirconium oxide and lanthanum oxide in cerium oxide. Hence, these new materials are the most significant enablers for the lower NO-N02 standards required for 2004 and beyond. 

Sulfur oxides and nitrogen oxides may be removed from combustion gases by various processes. One of the cost-effective and efficient methods involve dry scrubbing of SOx and NOx over lanthanide-oxygen-sulfur compounds (Jalan and Desai 1992). Cerium sulfate is found to be an effective catalyst toward the reduction of NOx by ammonia. A combined removal of NOx and SOx has been achieved using cerium oxide doped with strontium oxide, lanthanum oxide, calcium oxide, or cerium sulfate. 

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