CATALYSED SOOT FILTER

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A catalysed soot filter for a diesel engine for increasing the percentage of NO2 of total NOx in exhaust gas exiting the catalysed soot filter relative to the percentage of NO2 of total NO in exhaust gas entering the catalysed soot filter comprises a wall flow substrate comprising an inlet end, an outlet end, a substrate axial length extending between the inlet end and the outlet end, and a plurality of channels defined by internal walls of the wall flow substrate, wherein the plurality of channels comprise a plurality of inlet channels having an open inlet end and a closed outlet end and a plurality of outlet channels having a closed inlet end and an open outlet end, wherein surfaces of the internal walls of the plurality of inlet channels comprise a wash coat of at least one inlet coating composition comprising at least one refractory metal oxide, an optionally stabilised rare earth metal oxide or a mixture of at least one refractory metal oxide and an optionally stabilised rare earth metal oxide and at least one catalytically active metal selected from the group consisting of platinum, palladium, iridium, rhodium, silver, gold and mixtures of any two or more thereof, which at least one inlet coating composition extends for an axial inlet coating length from the open inlet end to a downstream inlet coating end, wherein the axial inlet coating length is less than the substrate axial length, wherein external surfaces of the internal walls of the plurality of outlet channels comprise a washcoat of at least one on-wall outlet coating composition comprising at least one refractory metal oxide, an optionally stabilised rare earth metal oxide or a mixture of at least one refractory metal oxide and an optionally stabilised rare earth metal oxide and at least one catalytically active metal selected from the group consisting of platinum, palladium, iridium, rhodium, silver, gold and mixtures of any two or more thereof, which at least one on-wall outlet coating composition having a mean particle size (D50) of between 4 and 15 µm and extending for an axial outlet coating length from an upstream outlet end to the open outlet end, wherein the axial outlet coating length is 55 to 90 % of the substrate axial length and wherein the axial outlet coating length is greater than the axial inlet coating length. The invention also comprises an exhaust system 40 comprising a CSF 8 according to the invention. In a preferred embodiment, the CSF is disposed upstream of a substrate monolith 6 comprising a selective catalytic reduction catalyst.