Device and application thereof for distributing a multiphase mixture having at least one gas phase including, e.g., hydrogen in part and at least one liquid phase, the mixture being in a downward flow through at least one bed of granular solids, the device including, at least one distributor plate located above one of the beds of granular solids at a distance "d", and several mixing channels of the liquid and gas phases of the mixture. Each of the channels has at least one upper passage section and at least one lower passage section allowing communication between the mixture formed in the mixing channels with a bed of granular solids. The mixing channels are provided on at least part of their height with one or more lateral passage sections, the upper passage section allowing the majority of the gas phase of the mixture to pass and the lateral passage sections allowing passage of the liquid phase and/or at least part of the gas phase inside the mixing channels. The density value of the mixing channels is greater than 80 channels per square meter.