Catalyst, its production and its use for the gas-phase polymerization of conjugated dienes

Catalysts consisting of A) an alcoholate of the rare earths, a carboxylate of the rare earths, a complex compound of the rare earths with diketones and/or an addition compound of the halides of the rare earths with an oxygen or nitrogen donor compound, B) an aluminium trialkyl, a dialkyl aluminium hydride and/or an alumoxane, C) another Lewis acid and D) an inert, particulate inorganic solid with a specific surface of greater than 10 m2/g (BET) and a pore volume of 0.3 to 15 ml/g are eminently suitable for the polymerization of conjugated dienes, more particularly butadiene, in the gas phase.