Precious metals auto catalysts

The precious metals possess much higher specific catalytic activity than do the base metals. In addition, base metal catalysts sinter upon exposure to the exhaust gas temperatures found in engine exhaust, thereby losing the catalytic performance needed for low temperature operation. Also, the base metals deactivate because of reactions with sulfur compounds at the low temperature end of auto exhaust. As a result, a base metal automobile exhaust... 

The alkylated anthraquinone process accounts for over 95% of the world production of H202, mainly because the it operates under mild conditions and direct contact of 02 and H2 is avoided. In this process, 2-alkylanthraquinone (the alkyl group is typically an ethyl, terf-butyl or amyl group) is dissolved in a mixture of a non-polar solvent (C9-Cn alkylbenzene) and a polar solvent [Trioctyl phosphate (TOP), or tetrabutyl urea (TBU) or diisobutyl carbinol (DIBC)] and then hydrogenated over a precious metal (Pd or Ni) catalyst in a three-phase reactor (trickle bed or slurry bubble column) under mild reaction conditions (<5bar, <80 °C) to generate 2-alkylanthrahydroquinone [1-3, 5], The latter is then auto-oxidized with air in a... 

Based on the catalyst requirements for export models and the expected penetration of catalyst cars in Western Europe the precious metal requirements for auto catalysts is forecast to be 375,000 oz in Europe by 1994 (Ref. 13). 

Among non-precious metals, copper-chromium combinations seem to be the most effective catalysts for CO exhaust elimination. For example, monoliths and pellets impregnated with copper-chromite have been reported to have activities near those of precious metal-based auto-emission control catalysts (ref. 1,2). This comparison has also been extended to the oxidation of CO with NO (ref. 3,4), another important auto-emission pollutant. 

U.S. emissions standards (LEV ULEV) in the late 1990 s will require catalysts with improved HC removal and probably at least some NOx reduction activity, as well. Emissions standards for diesel autos in Europe will require improved HC removal to meet EURO II levels for HC + NOx- Catalyst "C" has been reformulated with additional oxide components and varying precious metal loadings to address these needs. The new type of catalyst, designated Catalyst "D" in this paper, has been found to exhibit improved HC removal, especially at low exhaust temperatures. 

Before the TWC concept was even discussed, it had become clear that precious metals (the industry term for Pt, Pd, Rh) were indispensable ingredients in the auto catalyst. Despite their high cost and occasional problems of availability, the margin of superiority over base metals was too great. 

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