Selective catalytic reduction catalyst

A method and a selective catalytic reduction composition for converting NOx in an exhaust gas. The composition comprises a mixture of two components, the first being the H-form of an aluminosilicate chabazite zeolite (CHA) alone or in a mixture with the H-form of an aluminosilicate mordenite zeolite (MOR) in a weight ratio preferably of 5:3 to 3:5 and the second is a vanadium oxide supported on a metal oxide e.g. titania and/or a silica-stabilised titania, wherein the weight ratio of the first component to the second is 10:90 to 25:75. The metal oxide may also comprise tungsten oxide. The composition can comprise a binder e.g. clay, alumina and/or glass fibres and the weight ratio of the two components to the binder may be 80:20 to 95:5. The vanadium oxide can comprise iron vanadate and may be present as 0.5-5wt% V2O5. The composition may be a washcoat comprising fillers, binders, processing aids, water and dopants and may coat a substrate monolith e.g. a metal-flow through, a ceramic or a wall-flow, a sintered or a partial filter to form a catalyst article. The article can be an extruded honeycomb monolith and may also comprise an ammonia slip catalyst composition.