Abstract: A catalyst suitable for the catalysis of the oxidation of carbon monoxide is prepared by providing the substrate with tin (IV) oxide support material and with a catalytically active material.The tin (IV) oxide is provided by contacting the substrate with a dispersion of colloidal or non-colloidal particles in a liquid medium, said dispersion being convertible to tin (IV) oxide by drying and firing, followed by drying and firing. A catalyst can be so-produced having low flow resistance, high low temperature activity and relative insensitivity to deactivation by moisture. The dispersion may, for example, be a tin (IV) oxide aqua-sol made, for example, by peptising hydrated stannic oxide with a quaternary ammonium hydroxide.