Disclosed herein is an apparatus and a method for catalytic conversion of chemical substances in the presence of pulverulent catalysts in a trickle bed reactor with residence times in the range of 0.1-10 seconds, wherein the apparatus includes a trickle bed reactor (2), the inlet side of which is functionally connected to a catalyst reservoir vessel (1) and a reactant feed, and the outlet side of which is functionally connected to a separator (3). The separator (3) has an exit conduit for leading off product stream, wherein the apparatus has the characteristic feature that the exit conduit disposed on the separator (3) for leading off product stream has a continuously acting valve connected via a controller to a pressure measurement sensor, wherein the continuously acting valve and the pressure measurement sensor form a pressure control circuit with a controller.