Coating a monolith substrate with catalyst component

A method of coating a honeycomb monolith substrate comprising a plurality of channels with a liquid comprising a catalyst component, which method comprising the steps of:

• (i) holding a honeycomb monolith substrate substantially vertically;
• (ii) introducing a pre-determined volume of the liquid into the substrate via open ends of the channels at a lower end of the substrate with a liquid introducing means, wherein the liquid introducing means comprises a piston that reciprocates within a cylinder;
• (iii) sealingly retaining the introduced liquid within the substrate;
• (iv) inverting the substrate containing the retained liquid;
• and
• (v) applying a vacuum to open ends of the channels of the substrate at the inverted, lower end of the substrate to draw the retained liquid along the channels of the substrate.