PRODUCT INFORMATION
INDEX
DATE
Dep. 2
IC-C-D-40-003e A
May 2012
OXIDATIVE CATALYTIC CONVERTERS
6/6
6. LOSS OF ACTIVITY IN THE CATALYTIC CONVERTER
The activity of a catalytic converter drops progressively over time, although a series of mechanisms can cause
said activity to be lost before the end of its useful life, significantly reducing exhaust pollutant reduction efficiency
as shown on the following table:
Mechanism
Description
CHEMICAL
POISONING
Poisons are those elements or compounds which are present in engine exhaust gases and
combine chemically with the materials of the catalytic converter, causing them to lose activity. In
most cases when poisoning occurs the damage is irreversible.
CATALYTIC
INHIBITION
Inhibitors are those elements that, when present in engine exhaust gases, can make the catalytic
converter lose efficiency in certain operating conditions. However, the catalytic converter recovers
its normal performance when the inhibitor is not present in the exhaust gases or when operating
conditions change. One example of this is sulphur, which does not allow the catalytic converter to
operate correctly at low temperatures, and acts as a poison. When the system starts operating at
high temperatures it is eliminated and normal efficiency levels are regained.
DIRTYING OR
MASKING
The loss of activity by a catalytic converter through dirtying or masking happens when an inert
residue or ash from the exhaust gases is deposited on the catalytic surface, blocking it and
preventing it from working correctly. In many cases, the residue can be eliminated from the
catalytic surface using cleaning methods that allow it to regain normal catalytic converter activity
levels.
THERMAL
DEACTIVATION
Thermal deactivation of the catalytic converter happens when the creep temperature of the
materials that make it up is exceeded. This type of problem can happen as a result of a sudden
increase in the pollutants to be eliminated which, when they are converted through exothermic
reactions, cause the thermal limits of the materials of the catalytic converter to be exceeded,
causing irreversible damage to its structure.
MECHANICAL
EROSION AND
DEACTIVATION
The erosion of the materials making up the catalytic converter substrate is due to natural causes
(time) or to wear caused by an excessive presence of solid materials in the exhaust gas.
Mechanical deactivation means that the internal channels of the catalytic converter become
blocked or their walls collapse due to mechanical problems (excessive vibration, blows, excessive
erosion, etc.). This type of damage to the catalytic converter is irreversible.
Table 5. Causes of loss of activity in the catalytic converter.
2.7.6
O&M_2.002211.810_A_10_2016
