Process for preparing abrasion-resistant coated catalysts

Claim 1

A process for preparing abrasion-resistant coated particulate catalysts formed of an inert particulate support which has a rough surface and a particle size range of 0.5 to 6 mm and a coating of catalytically active material enclosing said inert support and anchored to said support, said process comprising providing a bed of said support located in a cylindrically or conically shaped horizontal zone having a horizontal axis of rotation, agitating said bed and spraying onto said bed a suspension of a pulverulent precursor for the catalytically active material in a suspending medium, while partially removing the suspending medium by a gas stream at a temperature of 20°-250° C., to thereby deposit a coating of the said pulverulent precursor on said support while maintaining essentially constant residual moisture of the coating during the build up of the coating on the inert support, said agitating being accomplished by imparting a mixing motion to the support bed located in said horizontal zone by mechanical action of rotation of said axis of rotation, simultaneously loosening and thereby agitating the support bed by blowing in from below a fluidizing, mixingintensifying gas stream; and at the same time passing a suspension of the precursor for the catalytically active material, which suspension contains a binder, countercurrent to the gas in this bed at a rate which increases with increasing thickness of the coating, the amounts of suspending medium being removed by said gas and the amount of suspending medium being passed countercurrent to the gas being maintained in a substantially constant ratio which is determined by the particular combination of support and precursor used, the thermal expansion coefficients of support and of dried pulverulent precursor being so chosen that they differ by at most 15%, and after completing the passing of the suspension in countercurrent flow with the gas, increasing the density of the coating being formed on said particulate support by continuing the increased mixing motion, thereafter stopping the mechanical mixing motion upon reaching the desired density and drying the coated support in ancontinuing gas stream wherein the spraying of the said suspension and the drying of the coated support are carried out in said cylindrically or conically shaped horizontal zone having said axis of rotation, the said fluidizing, mixing-intensifying gas stream being introduced exclusively from beneath said support bed through means for introducing said gas stream arranged on the outside in an outer jacket of said horizontal zone, and through perforated hollow ribs arranged on the inside of said horizontal zone, the perforations on the hollow ribs being oriented away from the direction of rotation of said axis of rotation, and finally heat-treating the coated support.