Exhaust system for a compression ignition engine comprising a water adsorbent material

A diesel engine exhaust system comprising an oxidation catalyst, wherein the oxidation catalyst comprises:

• a water adsorbent material consisting of a zeolite having a silica to alumina ratio (SAR) of 35:1 to 8:1, wherein the zeolite is at least one of a transition metal ion-exchanged zeolite, a zeolite impregnated with a transition metal ion, or a non-transition metal ion-exchanged zeolite that is not impregnated with a transition metal ion,
• a catalyst composition for treating an exhaust gas pollutant produced by the compression ignition engine wherein the catalyst composition comprises a platinum group metal (PGM) and a support material, wherein the platinum group metal comprises platinum;
• and
• a substrate;
• wherein the catalyst composition and the water adsorbent material is each disposed on the substrate, and wherein a first washcoat zone is disposed at an inlet end of the substrate and a second washcoat zone is disposed downstream of the first washcoat zone, wherein the first washcoat zone consists of the water adsorbent material and the second washcoat zone comprises the catalyst composition, wherein the water adsorbent material is arranged to contact exhaust gas directly from the diesel engine, and wherein there is no emissions control device upstream of the oxidation catalyst.