A shell-and-tube reactor is disclosed. Contact tubes are disposed within a cylindrical housing and are secured to tube plates. Gas and liquid phases are received via a feed opening in a lower end cap and discharged via an upper end cap in the housing. A distributor device for a gas phase/liquid phase mixture is disposed below the lowermost tube plate. The distributor device includes a distributor plate and a predistributor. The distributor plate is arranged horizontally within the housing and includes an active area having through-openings and a downward-extending margin, but does not extend over the entire cross section of the housing. The predistributor includes a second distributor plate disposed between the feed opening and the first distributor plate, wherein the second distributor plate includes a second active area with second through-openings and a second downward-extending margin.