POLLUTION-CONTROL OF DIESEL EXHAUST USING OXIDATION CATALYSTS

The survival of the diesel engine in the future will depend on the dev elopment of a really efficient, reliable process to be easily implemen ted for the pollution control of exhaust gases. The particulate filter can be proved to be efficient for a short while, but its periodic reg eneration could present a solution to the tricky problems of control a nd implementation costs. Another solution, contemplated in the past an d then discarded, is being considered again: this is the catalytic oxi dation of gaseous unburnt residues. Excess oxygen contained in diesel exhaust gases does not allow the use of three-way catalysts to reduce emissions of nitrogen oxides as for the spark-ignition engines, but it furthers the elimination of all the combustible residues contained in gases by oxidation. The efficiency of such a technique is dependent u pon the sulphur content of the diesel fuel Specific catalytic formulat ions are required in order to avoid the generation of sulphur trioxide SO3, and then sulphuric acid contained in the form of sulphate partic ulates in exhaust gases or sulphate deposits on the catalyst. All the problems encountered, as well as the results of the tests performed in different types of new catalysts under development for this applicati on, are presented The influence of a number of parameters relating to catalyst design (support, wash-coat, metal, etc.) and their implementa tion conditions are studied.