Abstract: Moulded body based on pyrogenically prepared silicon dioxide, having an annular cylindrical form, the cross section of which has a void and wherein the free surface area accounts for from 1.6 to 77% of the total surface area of the cross section. Supported catalyst which contains on a support (moulded body) as the catalytically active components palladium and/or compounds and alkali metal compounds thereof, as well as additionally gold and/or compounds thereof (Pd/alkali metal/Au system) or cadmium and/or compounds thereof (Pd/alkali metal/Cd system) or barium and/or components thereof (Pd/alkali metal/Ba system) or palladium, alkali metal compounds and mixtures of gold and/or cadmium and/or barium. The catalyst is on a support having a channel which passes through it, and the active components exhibit a penetration depth of more than 0.5 mm to 1.5 mm, calculated from the surface of the support material.