A NITROGEN OXIDE STORAGE CATALYST

摘要

The invention relates to a nitrogen oxide storage catalyst which contains at least one catalyst material and at least one nitrogen oxide storage component from the group of alkali and alkaline earth metals. The nitrogen oxide storage catalyst is characterised in that the nitrogen oxide storage component, after completing catalyst preparation, is present as finely divided barium sulfate, strontium sulfate or as a mixture or mixed crystals of the two sulfates or as their complete or incomplete decomposition product with an average particle size of less than 1 .mu.m. Barium sulfate and/or strontium sulfate act as feed materials for the active storage component barium oxide in the storage catalyst according to the invention. As a result of the reductive exhaust gas compositions occurring under normal driving conditions barium sulfate and strontium sulfate decompose to compounds which are able to store nitrogen oxides. This more or less compensates for the loss of active storage components which occurs due to ageing. There is also the possibility of decomposing barium sulfate and/or strontium sulfate during production by means of reductive calcination in order to obtain a high initial loading of the catalyst with storage compounds. In this case the sulfates mentioned are used as auxiliary agents in order to introduce the highest possible concentrations of storage compounds into the storage catalyst.