An apparatus for converting a gaseous and/or liquid feed fluid to gaseous and/or liquid products using a solid catalyst comprises a reactor, a liquid phase disposed within the reactor volume, a fixed catalyst at least partially disposed in the liquid phase, a cooling system having a cooling element in thermal contact with the liquid phase, a feed inlet positioned to feed the feed fluid into the reactor volume, and a fluid outlet in fluid communication with the liquid phase. The catalyst is contained in a catalyst container and the container may be adjacent to said cooling element, extend through said cooling element, or may surround the catalyst container. The catalyst may be a Fischer-Tropsch catalyst.