Catalysts fluorite

Ceria is another type of mixed conducting oxide which has been shown already to induce electrochemical promotion.71 Ceria is a catalyst support of increasing technological importance.73 Due to its nonstoichiometry and significant oxygen storage capacity it is also often used as a promoting additive on other supports (e.g. y-A Cb) in automobile exhaust catalysts.79 It is a fluorite type oxide with predominant n-type semiconductivity. The contribution of its ionic conductivity has been estimated to be 1-3% at 350°C.71... 

In order to improve the resistance of Ni/Al203-based catalysts to sintering and coke formation, some workers have proposed the use of cerium compounds [36]. Ceria, a stable fluorite-type oxide, has been studied for various reactions due to its redox properties [37]. Zhu and Flytzani-Stephanopoulos [38] studied Ni/ceria catalysts for the POX of methane, finding that the presence of ceria, coupled with a high nickel dispersion, allows more stability and resistance to coke deposition. The synergistic effect of the highly dispersed nickel/ceria system is attributed to the facile transfer of oxygen from ceria to the nickel interface with oxidation of any carbon species produced from methane dissociation on nickel. 

Erom HRTEM studies, it is proposed that the majority of the bismuth molybdate phases can be derived from the fluorite structure, in which both the cation and anion vacancies can be accommodated within the fluorite framework (Buttrey et al 1987). Several industrial processes containing multicomponent bismuth molybdates may suffer loss of Mo oxides by volatilization under operating conditions, resulting in the loss of catalytic activity. Monitoring the catalyst microstructure using EM is therefore crucial to ensuring the continuity of these catalytic processes. 

Cerium oxide, or ceria (Ce02), is a component of an autoexhaust catalyst that crystallizes to the fluorite structure [45], In the fluorite structure of Ce02, a CCP framework of Ce4+ ions is formed, where the eight tetrahedral sites present in the FCC structure are occupied by O2 ions (see Figure 2.16, where the links between atoms to make the tetrahedral positions clear are shown) [52],... 

Ce02 with fluorite-type structure is a component in N02 dissociation catalysts [57] and biomass gasification catalysts [58],... 

Zamar F., Trovarelli A., Leitenburg C. and de Dolcetti G., Ce02-based solid solution with the fluorite structure as novel and effective catalysts for methane combustion. J. Chem. Soc. Chem. Commun. (1995) pp. 965-966. 

Ceria-based catalysts are intensively used because of their high chemical and physical stability, high oxygen mobility and high oxygen vacancy concentrations, which are characteristic of fluorite-type oxides. The possibility of cycling easily between reduced and oxidized states (Ce Ce" ) permits the reversible addition... 

Pale yellow cerium dioxide (ceria, ceric oxide) has the fluorite structure and is used in catalysis" ", solid oxide fuel cells (SOFC)", thin film optical waveguides" , reversible oxygen storage materials for automobile catalysts" and for doping copper oxide superconductors". The diverse cerium enolate precursors and deposition methods used in the formation of cerium oxide thin films are summarized in Table 6, whereby the most common precursor for ceria is Ce(thd)4. 

There has been a strong effort to rationalise and elucidate a structural principle which will account for all the anion-deficienl, fluorite-related, mixed-valent binary oxides of cerium, praseodymium and terbium. This is a key step not only for the solid-state chemistry of these materials but also for a large class of fluorite-related materials involved in applications such as fast oxygen conductors and as catalysts. The two main theoretical approaches to the problem were developed by Martin and by Kang and Eyring, and will be illustrated in the following sections. 

For the last twenty years, the research effort on ceria-based catalytic materials has steeply increased (I). An important part of this effort has been devoted to M/Ce02 and closely related systems, i.e. catalysts consisting of transition metals supported on the higher rare earth oxides (Ce02, Pi02-x Tb02-it), and ceria-containing mixed oxides, all of them with fluorite-related structure. 

Vargas, J.C., Libs, S., Roger, A.-C., and Kiennemann, A. Study of Ce-Zr-Co fluorite-type oxide as catalysts for hydrogen production by steam reforming of bioethanol. Catalysis Today, 2005, 107-108, 417. 

We prepared by sol-gel some thermally stable Zro.io(Cei-xPrx)o.9o02 mixed oxides (x between 0 and 0.75) with a fluorite-type structure. This structure was confirmed by the presence, in the Raman spectrum, of a single band ca. 460 cm characteristic of the M-0 vibration in the fluorite-type structure. Moreover, the band position and the shoulder at 570 cm indicate the presence of oxygen vacancies probably associated with praseodymium cations. Consequently, high OSCs appears to be the result of the presence of both cerium and praseodymium atoms. Thus, addition of praseodymium atoms into zirconia-ceria oxides appears to be very promising for the design of new automotive catalysts. 

OPCM route of ceria—zirconia solid solutions synthesis appears to be reasonably flexible approach allowing to make rather broad substitution in cation and anion sublattices of fluorite-like oxides without appearance of new phases provided homogeneous mixing of starting salts is ensured. Reasonably high dispersion of samples thus obtained and disordered bulk and surface structure makes them promising candidates as catalysts and supports for red-ox reactions. 

Acid-spar AI3-01166 Calcium difluoride Calcium fluoride Calcium fluoride (CaFa) EINECS 232-188-7 Fluorite Fluorspar HSDB 995 Irtran 3 Liparite Met-spar Natural fluorite. Source of fluorine, flux, ceramics, phosphors, paint pigment, catalyst in vrood preservative, spectroscopy, electronics, lasers, high-temperature dry-film lubricants. Solid mp = 1403° bp = 2500° d = 3.18 insoluble in H2O LD50 (gpg orl) > 5 g/kg. Cerac G Silicones Noah Chew. Solvay Deutschland GmbH. 

A certain amount of Ca is incorporated into the Ce02 matrix to form a fluorite-type solid solution with a solubility limit around 20%. According to XPS results the surface composition was approximately equal to the bulk. There is a small enrichment of Ca on the surface for solids with low Ca content. The surface area of the catalysts prepared did not differ significantly. 

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