Abstract: Apparatus for catalytic processes such as desulphurization of hydrocarbons comprises an upright reactor vessel containing at least one tray, and catalytic support means for one or more catalyst beds said support means are attached to the inner wall of the reactor and having filter units attached to render them permeable to fluids and impermeable to catalyst particles; located beneath each supporting means is a fluid permeable tray which is impermeable to catalyst particles and located beneath each tray at least one filter unit of equal or coarser filtering effect than the filter units attached to said supporting means, to prevent access of the catalyst particles to the underside of said tray.