A reactor comprises a reactor vessel defining a confined reactor volume, a support assembly extending about a periphery of the confined reactor volume, a basket positioned within the reactor vessel and supported by the support assembly, the basket having an interior surface and an exterior surface, a downflow zone being defined between the exterior surface of the basket and an interior surface of the confined reactor volume, an inlet screen positioned adjacent to one end of the interior surface and an outlet screen positioned adjacent to an opposite end of the interior surface, an upflow zone defined between the inlet screen and outlet screen, the inlet screen and the outlet screen containing a quantity of particulate catalyst, and a circulating device positioned above said upflow zone and configured to continuously circulate fluid upwardly though said upflow zone and downwardly through said downflow zone, the support assembly and the basket configured to promote the formation of a fluid vortex within a portion of the downflow zone.