Cerium oxide, deposition

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. 

A fascinating study on the surface science of copper hydride on Si02, as well as on AI2O3, ceria (cerium oxide), and ZnO, has appeared [50]. Pure, yet thermally unstable, CuH can be precipitated as a red-brown solid from aqueous cupric sulfate and hypophosphorous acid in the presence of H2SO4, and has been characterized by powder X-ray diffraction (PXRD) (Eq. 5.25). Transmission electron microscopy (TEM) data suggest that it is most stable when deposited on acidic Si02. 

The ACC is a stainless steel cylinder 3 in. in diameter and 1 ft long through which exhaust gases pass before they enter the muffler and tailpipe. The converter contains an extmded ceramic honeycomb stmcture with square pores 0.5 mm in diameter through which gases pass. The walls of these pores are coated with porous y-Al203 on which Pt, Pd, and Rh are deposited, along with several catalyst promoters such as cerium oxide. The residence time in the ACC is -0.05 sec, because the volume of gas that must be processed... 

The metal surface is covered with cerium oxide and the thickness of the film increases with time of immersion of the sample in the CeCl3 solution. Deposition and growth of islands of rare earth oxide have been observed. The islands may be associated with anodic and cathodic sites located in the microstructure of the metal. 

Recently, gold has emerged as one of the most active catalysts for alcohol oxidation and is especially selective for poly alcohols. In 2005, Corma [184] and Tsu-kuda [185], independently demonstrated the potential of gold nanoparticles for the oxidation of aliphatic alcohols. For example, in the case of gold nanoparticles deposited on nanocrystalline cerium oxide [184], a TOF of 12 500 h 1 was obtained for the conversion of 1-phenylethanol into acetophenone at 160 °C (Fig. 4.67). Moreover this catalyst is fully recyclable. Another example of a gold catalyst with exceptional activity is a 2.5% Au-2.5% Pd/Ti02 as catalyst [186]. In this case for 1-octanol a TOF of 2000 h-1 was observed at 160 °C (reaction without solvent, Fig. 4.67). 

Cerium oxide (CeO ) was deposited onto a (100) LaAlOj single-crystal substrate with a single cube texture and good in- and out-ofplane alignment. A cp scan of the (220) plane of the CeO film yielded a FWHM of 2.45 ° 0.05 ° the rocking curve of the (200) plane indicated a FWHM of 1.688° 0.006°. A layer of YSZ was then deposited by CCVD on top of this ceria layer. The majority of the YSZ deposited as one cube texture (Figure 3) with only a minor 45° film rotation (<1% intensity) present. The... 

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. 

TABLE 6. Deposition studies of cerium oxide (Ce02) films... 

TABLE 7. Deposition studies of lanthanide and actinide oxide films other than cerium oxide... 

Hardacre el al. (7 75, 174) investigated the properties, structure, and composition of cerium oxide films prepared by cerium deposition on Pt(lll), finding that the activity for CO oxidation is enhanced on Pt(lll) that is partially covered by ceria. It was suggested that new sites at the Pt-oxide interface become available for reaction. A remarkable observation is the high activity for CO oxidation when the Pt(lll) sample is fully encapsulated by ceria (Pt was undetectable by XPS and AES). It was proposed that an ultrathin, disordered ceria film becomes the active catalyst. It was also demonstrated by XPS and AES that Pt dramatically increases the reducibility of cerium oxide that is in intimate contact with Pt. This result suggests that intimate contact between the noble metal and oxide phases is indeed crucial to facile oxygen release from ceria. High-resolution electron microscopy demonstrated the presence of direct contact between ceria and noble metal for supported Pt-Rh catalysts (775). Hardacre et al. (173,174) related the catalytic activity of the ceria phase to partially reduced cerium oxide. 

Ethylbenzene dehydrogenation is generally catalyzed by a potassium-promoted iron oxide catalyst. The most widely used catalysts are composed of iron oxide, potassium carbonate, and various metal oxide promoters. Examples of metal oxide promoters include chromium oxide, cerium oxide, molybdenum oxide, and vanadium oxide. " The potassium component substantially increases catalyst activity relative to an unpromoted iron oxide catalyst. Potassium has been shown to provide other benefits. In particular, it reduces the formation of carbonaceous deposits on the catalyst surface, which prolongs catalyst life. 

Similarly, Fig. 75 shows the effect of both the amount and the type of precious metal on the extent of the solid state reaction between aluminum oxide and cerium oxide, leading to the formation of cerium aluminate. The overall effect of these interactions is that the catalytic activity and the durability of the precious metals vary as a function of the type of washcoat oxide they are deposited on [45]. 

In electrolysis self-forming anode technology is used whereby cerium oxide coatings are deposited onto conducting ceramic substrates [37]. 

The modification of BEA zeolite by surface deposition of silica and impregnation with cerium oxide was studied as a tool to improve the selectivity of the reaction. The number of acid sites, particularly the strong ones, on BEA zeolite decreases with increasing amounts of silica deposited on its surface. Moreover, there is no severe pore blocking after deposition. On the contrary, cerium oxide impregnation affords a catalyst with decreased adsorption capacity because part of the cerium oxide is deposited in the channels of the zeolite crystals and blocks the porous system. In addition, cerium oxide modification creates new weak acid sites on the zeolite surface. Silica modification decreases catalytic activity but slightly increases selectivity with respect to all ortho-HAP, para-HAP and para-acetoxyacetophenone, in comparison to the unmodified BEA zeolite, and the stability of the catalyst is also improved after modification. The best reaction results are obtained over 16% cerium-oxide-modified catalyst, the selectivity with respect to the C-acetylated products being increased to about 70% while the conversion remains 60%-80%. 

This new single-step synthesis unites the simplicity of preparation and lower production costs, with the outstanding properties of the final catalysts. By the single-step procedure proposed here, deposition of dispersed nanoparticles of noble metals on ceramic supports with customised textural properties and shape was achieved. Noble metals including platinum, palladium, rhodium, ruthenium, iridium, etc. and metal oxides including copper, iron, nickel, chromimn, cerium oxides, etc on sepiolite or its mixtures with alumina, titania, zirconia or other refractory oxides have been also studied. 

Durrani,S. M. A.,Al-Kuhaili,M.F. and Bakhtiari, . A. (2008) Carbon monoxide gassensing properties of electron-beam deposited cerium oxide thin films. Sensors and Actuators B Chemical 134,934-9. 

Benzophenone tetracarboxyiic dianhydride vacuum deposition Cerium oxide vacuum pump fluids 2,2, 4,4, 5,5 -Hexachlorobiphenyl vacuum pump oils... 

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