Catalyst comprising iron oxide made by heat decomposition of an iron halide and a lanthanide

23A catalyst which is based upon an iron oxide and a compound of a lanthanide, of which iron oxide at least a portion is made by a process which involves heat decomposition of an iron halide, the lanthanide being in a quantity in the range of from 0.07 to 0.15 mole per mole iron oxide present in the catalyst, calculated as FeO; a process for the preparation of the catalyst; a process for the dehydrogenation of an alkylaromatic compound which process involves contacting a feed containing the alkylaromatic compound with the catalyst; and a method of using an alkenylaromatic compound for making polymers or copolymers, in which method the alkenylaromatic compound has been prepared by the dehydrogenation process.