Ammonia slip catalyst filter

A catalyst article for the treatment of an exhaust gas, the catalyst article comprising:

• a wall-flow filter substrate having inlet channels open at an inlet-end of the substrate and closed at an outlet-end of the substrate, the inlet channels adjacent outlet channels which are closed at the inlet-end of the substrate and open at the outlet-end of the substrate,
• the wall-flow filter comprising at least first, second and third catalytic layers, wherein:
• (i) the first catalytic layer extends from the inlet-end of the substrate and comprises a first SCR composition;
• (ii) the second catalytic layer is provided in or on the walls of the inlet channels, extending from the inlet-end of the substrate, and comprises a PGM-containing composition, wherein:
• when the second catalytic layer is provided on the walls of the inlet channel, the first catalytic layer is provided on the second catalytic layer, and
• when the second catalytic layer is provided in the walls of the inlet channels, the first catalytic layer is provided on the walls of the inlet channels;
• and
• (iii) the third catalytic layer is provided in or on the walls of the outlet channels, extending from the outlet-end of the substrate, and comprises a second SCR composition;
• wherein a ratio of the PGMs in the second catalytic layer in g per ft3 to the total amount of the first and second SCR compositions in the first and third catalytic layers in g per in3 is from 1.5:8 to 5:8.