Why rhodium in three-way automotive catalysts?

Conference · Fri Dec 31 04:00:00 EST 1993

OSTI ID:141989

Shelef, M ^[1]

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1. Ford Motor Co., Dearborn, MI (United States)

The three-way catalysts with Rh are in use for 12 years. The cost of Rh, now the dearest ingredient of TWC`s prompts the search for substitutes. These efforts may come to fruition sooner with a sounder grasp of the basic role of the Rh. The Rh is in the TWC because of its beneficial catalytic behavior towards the NO molecule as compared to the other noble metals used, Pt and Pd. In was established empirically in surface and catalytic work that Rh: (a) dissociates NO at lower temperatures; (b) on its surface NO prevails in competitive adsorption with CO; (c) is selective in the presence of hydrogen, ubiqitous under reducing conditions, for the formation of N{sub 2} instead of NH{sub 3}; (d) allows the reaction with reducing species under slightly oxidizing conditions in competition with O{sub 2}. The formation of dinitrosyl species on dispersed Rh catalysts may be responsible for (c) and (d). It also works in practice. First attempts at theory confirm the empirical observations and hint that Rh replacement may not be easy.

• OSTI ID: 141989
• Report Number(s): CONF-930304--
• Country of Publication: United States
• Language: English

Related Subjects

40 CHEMISTRY
54 ENVIRONMENTAL SCIENCES
AUTOMOBILES
CATALYTIC CONVERTERS
CATALYTIC EFFECTS
CHEMICAL REACTIONS
NITRIC OXIDE
RHODIUM