Diesel Oxidation Catalyst Application Strategies with Special Emphasis on Odour Reduction

The paper deals with problems arising on the one hand from aplying diesel oxidation catalyst for minimizing HC emission at low exhaust gas temperatures prevailing in the European city driving cycle and on the other hand in preventing sulphate formation in the oxidation catalyst at higher temperatures as they appear e.g. in the ECE R49 13-mode certification cycle. The main parameters influencing the catalyst efficiency - exhaust gas temperature level, sulphur content in the fuel and catalyst specifications - are discussed and new solutions to fulfill the conflicting requirements are presented. The use of a highly active catalyst for exhaust gas treatment only up to the temperature limit of sulphates formation and by-passing it in the high temperature range appears to be a viable solution. As a result of this strategy, the oxidation catalyst is applicable in a wide exhaust gas temperature range from 150 up to 550 degrees Celsius with negligible sulphate emissions and high conversion efficiencies of the particulate soluble organic fraction and of gaseous emissions HC, CO, aldehydes and odour.