PRODUCT INFORMATION
INDEX
DATE
Dep. 2
IC-C-D-40-003e A
May 2012
OXIDATIVE CATALYTIC CONVERTERS
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1. OXIDATIVE CATALYTIC CONVERTERS
Catalytic substrates consist of high-temperature resistant steel foils of alternating
layers of corrugated and flat strips 100, 200, 300 or 400 cpsi (cells per square inch).
The catalytic materials coated onto the surfaces of the channels consist of a refractory
inorganic oxide, various substances which act as chemical promoters and stabilisers,
and a combination of precious metals that can include platinum, palladium and
rhodium. The substrates provide high resistance to thermal and mechanical shocks,
while at the same time offering customers an economical alternative
to ceramic and metal substrates currently on the market.
2. OPERATING THE CATALYTIC CONVERTER
The oxidative catalytic converter is effective in controlling carbon
monoxide (CO), non-methane hydrocarbons (NMHC), volatile organic
compounds (VOC), formaldehyde (CH2O) and hazardous air
pollutants (HAPs) produced by gas engines. The oxidation catalytic
converter is also effective for the catalytic combustion of VOC
emissions from a variety of exhaust gas streams.
The temperature of the exhaust gases within the catalytic converter
is a very important factor with regard to obtaining a high degree of
conversion efficiency. In general, the higher the temperature, the
greater the efficiency obtained by the catalytic system, depending on the pollutant
being treated. The appropriate permissible temperature range should be greater than 400°C and less than 600°C.
These oxidation reactions are exothermic (they produce heat), meaning that the catalyser outlet temperature is
higher than the inlet temperature. The
T value throughout the catalytic converter depends on several factors,
such as the amount of contaminant or the degree of efficiency of the catalytic converter, but the temperature rise
is normally below 40ºC.
An oxidative catalytic converter requires a certain amount of oxygen in order to be able to operate correctly, which
is why they are not normally used in stoichiometric combustion engines. Due to the high oxygen requirements in
the exhaust, it is not viable to carry out NOx reduction reactions in this type of catalytic converter, meaning that
the presence of these pollutants in the exhaust flows remains practically the same. The amount of NOx in the
exhausts must be adjusted to comply with legal requirements concerning emissions by controlling the parameters
of the lean mix engine itself or by incorporating other processing systems.
OXIDATION REACTIONS THAT OCCUR IN THE OXIDATION CATALYTIC CONVERTER
CARBON MONOXIDE
CO + ½ O2
→
CO2
(1)
HYDROCARBONS
CmHn + (m + n/4) O2
→
m CO2 + n/2 H2O
(2)
ALDEHYDES, KETONES,
ETC.
CmHnO + (m + n/4 - 0.5) O2
→
m CO2 + n/2 H2O
(3)
HYDROGEN
H2 + ½ O2
→
H2O
(4)
Table 1. Contaminants that are reduced in a oxidative catalytic converter by utilising oxidation reactions.
2.7.1
O&M_2.002211.810_A_10_2016
