DOC Deactivation

W. Addy Majewski

This is a preview of the paper, limited to some initial content. Full access requires DieselNet subscription.
Please log in to view the complete version of this paper.

Abstract: The causes of diesel oxidation catalyst deactivation include thermal degradation, poisoning by lubrication oil additives and sulfur, and PGM oxidation. Phosphorus, the most common oil-derived catalyst poison, is selectively adsorbed at the catalyst inlet and in a thin, outer washcoat layer. Sulfur can be found uniformly distributed over the catalyst length and the washcoat depth. Some DOC deactivation modes are permanent, while others are temporary or reversible.


In early DOC applications, catalyst deactivation was not expected to be a major issue. Most catalytic materials used in early diesel catalysts had been developed for gasoline applications, where the maximum exhaust gas temperature and the temperature raise (exotherm) were much higher than those in diesel engines. With time, however, new materials have been introduced to DOC formulations (e.g., zeolites) that may require thermal stabilization, and diesel aftertreatment configurations have been developed where catalysts can be exposed to very high temperatures. An example is the heat-up catalyst used to support the regeneration of diesel particulate filters. Heat-up catalysts are exposed to both very high temperatures and to fouling by unburned hydrocarbons and coke—it is a very demanding catalyst application that requires excellent durability.

Most diesel oxidation catalysts utilize platinum group metals (PGM) such as Pt and Pd. Important modes of deactivation of PGM-based catalysts include [5628][5629]:

The first two deactivation modes are permanent, while sulfur poisoning and PGM oxidation are temporary or reversible, either partially or fully.