Catalytic reactions are carried out in a reactor which contains a liquid phase in which at least one catalyst is suspended, and which may additionally contain a gas phase, by a process in which the liquid phase and, if present, also the gas phase are fed, at least partly, through an apparatus having orifices or channels in the reactor, the hydraulic diameter of which orifices or channels is from 0.5 to 20 mm, preferably from 1 to 10 mm, particularly preferably from 1 to 3 mm.