Selective catalytic reduction catalyst on a filter

A selective catalytic reduction catalyst comprising

• a porous wall-flow filter 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 passages defined by porous internal walls of the porous wall-flow filter substrate,
• wherein the plurality of passages comprise inlet passages having an open inlet end and a closed outlet end, and outlet passages having a closed inlet end and an open outlet end,
• wherein an interface between the passages and the porous internal walls is defined by a surface of the porous internal walls;
• and wherein in the pores of the porous internal walls and on the surface of the porous internal walls, the catalyst comprises a selective catalytic reduction coating comprising a selective catalytic reduction component comprising a zeolitic material comprising one or more of copper and iron;
• wherein in the pores of the porous internal walls, the selective catalytic reduction catalytic coating is present as in-wall-coating, and on the surface of the porous internal walls, the selective catalytic reduction catalytic coating is present as on-wall-coating;
• and wherein in addition to the-selective catalytic reduction catalytic coating, the catalyst comprises no further coating in the pores of the porous internal walls and no further coating on the surface of the porous internal walls;
• and
• wherein the selective catalytic reduction coating is present at a total loading, I(total), which is the sum of the loading of the in-wall coating, I(in-wall coating), and the loading of the on-wall coating, I(on-wall coating), wherein in the catalyst, a loading ratio, defined as the loading of the on-wall coating, I(on-wall coating), relative to the loading of the in-wall coating, I(in-wall coating), the loading ratio, being defined as I(on-wall coating):I(in-wall coating), ranges from 17:83 to 80:20.