A catalyst comprising gold, palladium, and a porous support, in the form of at least one grain, in which: the gold content in the catalyst is in the range 0.5% to 3% by weight with respect to the total weight of catalyst; the mean particle size of the gold, estimated by transmission electron microscopy (TEM), is in the range 0.5 nm to 5 nm; the gold is distributed homogeneously in the porous support; at least 80% by weight of the palladium is distributed in an eggshell at the periphery of the porous support; the gold/palladium molar ratio is more than 2.