1992-02-01

Investigation of Catalytic Alternatives to Rhodium in Emissions Control 920846

With the world-wide growth of the automotive emissions controls market, concerns about the future cost and availability of catalytic metals, particularly rhodium, have also grown. These factors have led to an increased interest in catalyst formulations which might allow reduced Rh usage or the complete removal of Rh from the catalyst without compromising the performance of emissions control systems. We have tested a set of catalysts to examine Ru, Ir, and Pd as alternatives to Rh, either alone or in combination with Pt. For the nine catalysts of Pt, Rh, Pd, Ru, Ir, Pt/Rh, Pt/Pd, Pt/Ru, and Pt/Ir studied, the loading of all constituent metals on 85 cu. in. monoliths in single or 1:1 dual component catalysts was 0.038 oz t, except for Rh which had a 0.0038 oz t loading. Most of the monoliths were evaluated after 0, 6, and 75 hours on a rapid aging test schedule using sweep, light-off, dynamometer and/or vehicle tests using the Federal Test Procedure (FTP). After 75 hours of aging, which for present formulations is considered to be equivalent to 50,000 miles of vehicle aging, the Pt/Rh set outperformed all others in sweep and FTP testing, with the Pt/Pd set a close second overall. In comparison with the Pt-only data from the FTP tests after 75 hours of aging, the addition of Pd (or Rh) always improves the activity of Pt, whereas the addition of Ir or Ru leaves Pt's activity unchanged or, as in most cases, degrades it. While the use of Ru or Ir does not appear worthy of significant further effort, the Pt/Pd system deserves much more study in the pursuit of an alternative to the present Pt/Rh formulation.

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