Downflow catalytic reactor having a plurality of catalyst beds in which a mixture of gas and liquid are passed, the region in between subsequent catalyst beds being provided with a distributor system for the distribution and mixing of gas and liquid prior to contact with a subsequent catalyst bed, said region comprising: (a) gas injection line arranged below a catalyst support tray, (b) collector tray adapted to receive gas and liquid, (c) spillway collectors extending above the level of said collecting tray, (d) mixing chamber adapted to receive the gas and liquid descending from said spillway collectors, (e) impingement plate below said mixing chamber, (f) first distributor tray arranged below said impingement plate having a number of apertures throughout and a number chimneys, and (g) second distributor tray arranged below said first distributor tray for the redistribution of gas and liquid prior to contact with the subsequent catalyst bed, wherein the at least one chimney is provided with a distributor device that is able to divide the chimney chamber into at least two chambers.