substrate the palladium is impregnated onto the upstream support portion of the support medium using an acidic aqueous solution of palladium chloride 4 vol in concentrated hno 3 this solution is dried on the substrate at 130 u00b0 c and then calcined at 500 u00b0 c for a time period of 3 to 4 hours this results in approximately 0 18 by weight of the substrate of palladium being applied to the substrate over its upstream support portion although this preferred embodiment was prepared as outlined above there are a number of ways that a skilled artisan can vary the preparation for example instead of impregnating tungsten and gamma alumina in two consecutive steps on the downstream support portion of the support medium this process can be combined into one step also the gamma alumina need not be coated on a honeycomb but may be coated onto different support configurations such as a metallic substrate as required for different applications pelleted or extruded alumina can be used as a support medium in place of a monolithic support in this case one does not need a high surface area alumina washcoating step reference is now made to fig1 3 and 4 so that the benefits of the use of the catalyst system of this invention may be better understood in fig1 there is shown the effect.