Described herein are systems and methods for delivering catalyst to a reaction vessel. The methods include the use of a positive displacement reciprocating piston system having a catalyst delivery housing that contains a piston system. The piston system includes a top section, a bottom section, and a catalyst holding space between the top and bottom section such that the piston system is movable between a first and a second position to inject catalyst from the catalyst holding space into the reaction vessel when the piston system is in the second position and fill the catalyst holding space with catalyst from a catalyst feed supply when the piston system is in the first position.