An array of discrete catalyst elements is contained in a heated module external to the main laser vessel with an auxiliary gas flow loop connecting them so as to provide independent control of catalyst temperature and gas flow rate to achieve high CO+1/2O2 to CO2 recombination under high pulse repetition frequency operation for a sealed laser. Catalyst elements in the form of cylinders with holes through their centers are mounted on multiple parallel rods or catalysts in the form of small spherical or cylindrical elements are contained in multiple packets arranged in the module so as to minimize flow impedance and maximize laser gas recycling throughput. The cylindrical catalyst module is constructed so as to allow for rapid heating to operating temperature while withstanding atmospheric differential pressures during laser processing.