Particle extrusion

A method of making helically formed extrudate particles for use in catalysis, comprising the steps:

• providing an extruder with a die, the die comprising a plurality of channels extending from an inlet to an outlet, wherein from the inlet to the outlet each channel comprises a first section with a helical bore with a non-circular cross-section, and a second section with a cylindrical bore which has a diameter equal or greater than that of the first section, wherein the second section is at least twice as long as a diameter of the first section;
• preparing a starting mixture for extrusion;
• feeding the starting mixture through the die of the extruder;
• and
• separating extruded material from the die of the extruder to provide the helically formed extrudate particles.