Catalytic converters cerium oxide

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. 

Cerium(III) tris(/3-diketonate) complexes are readily oxidized to the cerium(IV) compounds. They are volatile with vapor pressures high enough for MOCVD use. A number of diketonates are now better characterised, prompted by the possibility of using them as CVD materials and petrol additives, as well as a source of cerium oxide as an oxygen store for catalytic converters. [Ce Me3CCOCHCOCMe2(OMe) 4], Ce(acac)4 (Figure 32), Ce(dbm)4, [Ce(pmhd)4], and Ce(tmhd)4 all have square-antiprismatic coordination of cerium (in the [Ce(catecholate)4]" ion the coordination is dodecahedral). 

The three-way exhaust catalytic converter is used to complete the combustion of carbon monoxide and unburned fuel elements and to remove the NO and N02 produced during combustion. The primary components of the catalytic converter are the catalyst and its physical support. The catalyst is composed of a high-surface-area support that incorporates the primary catalytically active materials, typically mixtures of one or more of platinum, palladium, or rhodium (precious group metals, PGMs). The catalyst also contains promoters that improve the efficiency and stability of the PGM. Of these, the most important is cerium oxide, a... 

The demand for the rare earth metals increased over the last two decades of the 20th century, and the demand for cerium oxides in motor vehicle catalytic converters (see equations 26.39 and 26.40) has been a major contributing factor. In 2001, the major use (34% of the total consumption) for rare earth metals in the US was in glass polishing and ceramics. Petroleum catalysts and catalytic converters... 

Summarize the operation of a three-way catalytic converter, including comments on (a) the addition of cerium oxides, (b) the light-off temperature, (c) optimum air-fuel ratios and (d) catalyst ageing. 

Cerium oxide is used in exhaust three-way catalytic converters where the emissions from fuel burning are converted to harmless gases. The conversion includes the following reactions ... 

An analogous activating-stabilizing function (or a more complex one) is displayed by 4f elements, Ce in particular, in the catalytic converter for exhausted gas from motor cars. Approximately 3-4% of cerium or other Ln oxide is incorporated within the catalyst pellets, in addition to noble metals (Pt, Pd, Rh). 

Nanosized cerium oxide also shows excellent properties. Oxalic and oxamic acid, aniline, and reactive dyes (C.I. Reactive Blue 5) could be effectively converted. The use of the catalyst significantly enhances the reaction rate and a synergetic effect between cerium oxide and carbon (used as the support) was noted. In addition, carbon is also active in the catalytic ozonation, and multiwall carbon nanotubes were shown to have high efficiency in the catalytic ozonation of oxalic and oxamic acids. 

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