homogeneously in the bulk of the palladium the homogeneous distribution of the other noble metal can be produced on the atomic scale for example when the combination is in the form of a homogeneous alloy the distribution of the other noble metal can also be produced on a more macroscopic scale such as for example the dispersion of small agglomerations of the other noble metal in the palladium or alternatively the formation of a thin layer of a coating of the other noble metal around the grains of palladium the other noble metal will preferably be chosen from palladium rhodium and gold it can also consist of a mixture of these metals of these noble metals gold is particularly preferred the proportion by weight of the other noble metal in the combination can vary within wide limits it is advantageous for it not to exceed 80 of the total weight of the metals of the catalyst and preferably 60 of the total weight of these metals the support of the catalyst comprises according to the invention at least one compound chosen from the sulphates or the phosphates of the alkaline earth metals or a mixture of the latter sulphate or phosphate is intended to designate an alkaline earth metal salt which contains the neutral sulphate so 4 monohydrogensulphate or acidic sulphate hso 4 neutral orthophosphate po 4 monohydrogenorthophosphate hpo 4 or.