The present invention relates to a method for preparing halogenated benzonitriles by vapor phase ammoxidation at a reaction temperature in the range of 300 to 500° C. in a fixed bed reactor using a three-component catalyst. More particularly, the method of the invention relates to a method for preparing 2,6-dichlorobenzonitrile (2,6-DCBN) from 2,6-dichlorotoluene (2,6-DCT) by vapor phase ammoxidation. The invention also relates to a three-component catalyst provided on a carrier and its use in a vapor phase ammoxidation reaction according to the invention. In addition, the invention provides a method for preparing the three-component catalyst.