Catalytic extruded, solid honeycomb body

A method of making an extruded, solid honeycomb body comprising the steps of:

• (a) forming a plastic mixture by mixing and/or kneading together a powdered diatomaceous earth matrix component;
• powdered additional matrix component;
• powdered small pore, crystalline molecular sieve, wherein the small pore, crystalline molecular sieve contains a maximum ring size of eight tetrahedral atoms;
• a copper component;
• optional inorganic fibres;
• and an acid or alkaline aqueous solution, wherein the copper component comprises copper which has been ion-exchanged in the small pore, crystalline molecular sieve prior to the mixing step and/or the copper component is added as an ion-exchange precursor to the mixture, wherein the powdered small pore, crystalline molecular sieve is added to the mixture as the H+ or NH4+ form thereof and the small pore, crystalline molecular sieve is ion-exchanged with the copper in situ, and wherein the plastic mixture is formed including an organic auxiliary;
• (b) extruding the plastic mixture into a wet honeycomb body, drying the extruded honeycomb body and calcining it to form an extruded, solid honeycomb body;
• and
• (c) selecting quantitative proportions of the starting materials such that the extruded, solid honeycomb body contains 20-50% by weight matrix component comprising diatomaceous earth, wherein 2-20 weight % of the extruded, solid honeycomb body is diatomaceous earth, and wherein the diatomaceous earth contains iron oxide;
• 80-50% by weight of the small pore, crystalline molecular sieve ion-exchanged with copper;
• and 0-10% by weight of inorganic fibres.