Combination of a Zeolite-Based SCR Catalyst with a Manganese-Based SCR Catalyst in the Bypass

摘要

The invention relates to an exhaust-gas aftertreatment system for selective catalytic reduction with a plurality of SCR catalytic converters, which exhaust-gas aftertreatment system is able to reduce NOx in a large temperature range and can store SOx. The invention further relates to a method for treating an exhaust gas flow, in which method the exhaust-gas aftertreatment system according to the invention is used. The system comprises a high-temperature SCR catalyst for temperature ranges between 250° C. and 750° C. and a low-temperature SCR catalyst arranged downstream thereof for temperature ranges between 60° C. and less than 250° C. There is a reductant supply system directly upstream of the high-temperature SCR catalyst. The high-temperature SCR catalyst is designed to reduce NOx in exhaust gas that has a temperature above a temperature threshold value and to store SOx in the temperature range below the threshold value. The low-temperature SCR catalyst reduces NOx in the temperature range below the threshold value. In each case, the exhaust gas flows through the high-temperature SCR catalyst. An exhaust-gas bypass valve or flow control valve is arranged directly upstream of the low-temperature SCR catalyst. If the temperature of the exhaust gas is greater than or equal to the temperature threshold value, the exhaust gas is completely conducted past the low-temperature SCR catalyst. The high-temperature SCR catalyst advantageously contains a molecular sieve as a catalytically active layer, and the catalytically active layer of the low-temperature SCR catalyst is preferably a manganese-containing mixed oxide.