Abstract: A process and apparatus for catalytic treatment of a material containing solid contaminants (in particular residue from hydrodesulfurization), the catalytic reactor being provided upstream of the catalyst bed with filter units small enough to be replaced via the reactor inlet, said filter units containing parallel void chambers alternately closed at top and bottom, respectively, (possibly by means of rupture discs), so that material to be filtered flows into a void chamber, through its wall which has filtering (and possibly also catalytic, e.g., demetallizing) properties, and then out of the next void chamber and onto the catalyst bed.