The conversion of nitrogen oxides (NOX) of a SCR system highly depends on the availability of ammonia (NH3) generated from the injected AdBlue® (32.5% aqueous urea solution).
In theory the optimal NH3/NOX ratio with 1:1 (ANR [Ammonia NOX Ratio] = 1) is given by the reaction stoichiometry. In practice the non-uniform ammonia distribution throughout the catalyst and the oxidation of ammonia at high temperatures in a SCR system leads to a higher ANR (ANR > 1) to achieve the maximum NOX conversion. An ANR > 1 usually results in an ammonia slip due to the fact that some channels of the honeycomb structured catalyst substrate get more ammonia than required for the SCR reaction and this excess gas passes through the catalyst. Especially if it is required to realize NOX conversion larger than 90 % or during dynamic operation cycles, the ammonia slip becomes an issue.
Gaseous ammonia has a very low smell threshold of approx. 15 ppm causing unpleasant odors and also leads to irritation of eyes and the respiratory system of a human being.
The task of the ammonia slip catalyst is the selective oxidation of the ammonia slip (NH3) to harmless nitrogen (N2) and water (H2O) and therefore avoiding smell and health risks.
2 NH3 + 3/2 O2 → N2 + 3 H2O
In combination with an adapted dosing strategy of urea, INTERKAT´s ASC technology enables our customers to raise the overall SCR conversion of their systems due to a higher applicable ANR ratio without the disadvantage of high ammonia slip. An additional benefit of our ASC is the oxidation of carbon monoxide (CO) and hydrocarbons (HC) e.g. formaldehyde (CH2O) passing the SCR catalysts. A customized catalyst design mostly prohibits the oxidation of ammonia to laughing gas (N2O) or nitrogen oxide (NO).
2 NH3 + 2 O2 → N2O + 3 H2O
2 NH3 + 5/2 O2 → 2 NO + 3 H2O
“INTERKAT will always provide the optimal catalyst for your application”