The study deals with the heterogeneously catalyzed gas-phase hydrogenation of cis,trans,trans-1,5,9-cyclododecatriene on coated catalysts prepared by anodic oxidation of aluminum and a liquid-phase impregnation technique. The coat of the catalyst consists of alumina having a regular pore system and palladium as a catalytically active component which is immobilized at the pore walls. The thickness of the coat which is equal to the pore length is adjusted in each catalyst to a certain size in the range of 5-30 mu m. The hydrogenation products are the intermediates cyclododecadiene and cyclododecene besides the completely saturated final product cyclododecane. The scope of the investigations is to find out the advantages of the prepared coated catalysts in comparison to a commercial hydrogenation catalyst and the interdependences between the thickness of the coat and product selectivities as a result of mass transport influences. It is shown that the formation of cyclododecene on the coated catalysts is predominant, and at conversions of more than 90%, the shorter the pore length of the coated catalysts, the higher the selectivity to cyclododecene.