| 摘要 |
This invention relates to a catalytic composite for treating an exhaust gas comprising a support which is a refractory inorganic oxide having dispersed thereon lanthanum, at least one other rare earth component and at least one noble metal component selected from the group consisting of platinum, palladium, rhodium, ruthenium and iridium. An essential feature of said catalytic composite is that the lanthanum be present as crystalline particles of lanthanum oxide which have an average crystallite size of less than about 25 Angstroms. The support may be selected from the group consisting of alumina, silica, titania, zirconia, aluminosilicates and mixtures thereof with alumina being preferred. Illustrative of the other rare earth components are cerium, neodymium, praeseodymium, dysprosium, europium, holmium and ytterbium. An important feature in manufacturing the catalytic composite is the dispersion of lanthanum oxide onto said refractory inorganic oxide support. In a specific example, lanthanum may be dispersed on alumina as follows. A solution of a lanthanum salt is mixed with a hydrosol of aluminum, particles are formed from said lanthanum containing hydrosol, calcined to form an inorganic oxide particle containing lanthanum oxide, ground to give a powder of alumina containing finely dispersed lanthanum oxide. This powder in turn can be mixed with another rare earth oxide such as cerium oxide to a slurry which in turn is used to coat a solid monolithic carrier. Finally, at least one noble metal component is dispersed on said coated solid monolithic carrier.
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