PGM-free washcoats for catalyzed diesel particulate filter applications

Abstract

The present invention provides new platinum group metal (“PGM”) free catalytic compositions that comprise silver and / or cobalt stabilized ceria. These compositions facilitate soot oxidation during the regeneration of diesel particulate filters (DPF) thereby replacing PGM formulations. The compositions of the invention are particularly useful as washcoat compositions for DPFs as part of an automotive after-treatment system. Among the formulations tested, the silver-stabilized ceria and cobalt-stabilized ceria formulations e.g. can oxidize soot at 250-300° C. in the presence of NO2 and oxygen, while silver-stabilized ceria can oxidize diesel soot even in the presence of oxygen as the sole oxidizing agent at these temperatures. A perovshite composition containing Ag—La—Mn was very active at temperatures above 300° C.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS [0001] This application is a division of U.S. patent application Ser. No. 10 / 418,767, filed Apr. 18, 2003, which claims the benefit of European patent application no. 02100389.2 filed on Apr. 18, 2002. Each of these applications is hereby incorporated by reference.BACKGROUND OF THE INVENTION [0002] 1. Field of the Invention [0003] In at least one embodiment, the present invention relates to a platinum-group-metal (“PGM”) free catalytic compositions and the use of such compositions as a catalytically active washcoat for regenerable catalyzed diesel particulate filter applications and for automotive after-treatment systems. [0004] 2. Background Art [0005] Environmental regulations in the United States and Europe have necessitated improvements in the removal of particles from diesel engine emissions. Typically, such particles are carbonaceous particulates in the form of soot. Presently, the most promising method for removing soot from engine exha...

AI Technical Summary

Benefits of technology

These compositions demonstrate soot oxidation activities comparable to Pt-containing DPFs, with the ability to catalyze soot oxidation in oxygen-containing atmospheres at low temperatures, offering a cost-effective and environmentally benign solution for diesel particulate filter regeneration.

Problems solved by technology

However, the regeneration by soot oxidation of diesel particulate filter requires elaborate solutions because the usually low temperatures of diesel exhaust gases are not favorable for soot oxidation.

A filter system which uses such a fuel-borne catalyst approach is complex and requires additional components such as a tank for fuel additives, an additive dosing system, infrastructure to refill the additive fuel tank, and the like.

Moreover, fuel-borne catalysts lead to the formation of ash accumulated on the filter with gradual loss of filter soot capacity and a decrease in time between regeneration events.

The PGM contained in these DPFs, usually in the form of a catalytic coating are very expensive.

The world demand on PGM use in automotive exhaust after-treatment is high, while PGM supply is limited.

Furthermore, PGM coatings are highly active in undesirable reactions such as oxidation of SO2 to SO3, with the following formation of sulfated ash and sulfated particulate.

This, however, leads to significantly lower activities in soot oxidation and thus efficiency.

In addition, PGM-containing washcoats / coatings are vulnerable to poisoning by sulfur compounds, particularly in the case of low Pt- or Pd-loading, respectively.

Therefore the aforementioned CRT™ and DPNR filters are economically and in terms of efficiency restricted to the use together with fuel of very low sulfur level.

The basic problem is to find an active catalyst, which would be able to replace PGM metals.

At present, there is no commercially applicable solution available to the problem of PGM-free catalysed DPFs, though attempts employing vanadium-containing catalysed DPFs have well been described.

These catalysts, however, exhibited no noticeable activity below 400° C., furthermore, they were not stable.

These vanadium-containing formulations though not being expensive, are highly toxic.

Furthermore, their relatively low melting point leads to inevitable noxious vanadium emissions from the filter during running due to the high temperatures developed in the course of soot combustion.

Among other catalysts, a very promising low temperature activity near 300° C. was reported for Cu—Nb (Ta)—K—La2O3 (TiO2), but Nb and Ta also are very expensive, annihilating any economical benefit.

In addition, the stability of the catalyst is low due to the presence of chlorides (A. Bellaloui, J. Varloud etc.

However, these catalysts are not attractive due to their low stability and high corrosive activity (S. J. Jelles, B.A.A.L. van Setten, M. Makkee, J. AS. Moulijn. Appl. Catalysis B: 1999, 21, 35-49; Cat.

Images