Deactivation of diesel oxidation catalysts: Vehicle- and synthetic aging correlations

Abstract

Deactivation characteristics of a diesel oxidation catalyst subjected to controlled lab aging were compared to field-aged catalysts after 0, 80,000, and 160,000km driving in order to establish the (dis)similarities between the two types of aging, and determine to what extent vehicle aging can be replaced by rapid synthetic aging. Emission tests confirmed the increasing deactivation of the field-aged catalysts and measurements of CO oxidation, Pt dispersion and hydrocarbon storage capacity were used together with XPS, TEM, and SEM–EDS to compare the performance with lab-aged catalysts. The synthetic aging was designed to account for a combination of thermal and chemical deactivation. A similar degree of Pt sintering was observed for both real and synthetic aging conditions, whereas differences arose from various contributions to the chemical deactivation. XPS showed that pre-oxidation and pre-reduction at 700°C was not sufficient to remove typical compounds of oil-derived catalyst poisons (P, Zn, Ca), which furthermore accumulated with mileage, on the vehicle-aged catalysts. The degree of sulfur poisoning of the lab-aged catalysts increased with the duration of low-temperature sulfur exposure and could not be recovered in atmospheres typical for normal driving conditions. The results show that synthetic aging can be used to simulate thermal aging and a general effect of irreversible chemical deactivation, and thereby accelerate durability test procedures of various catalysts where loss of catalytic activity by time of operation is of concern.