A series of alkali- and/or alkali-earth-promoted, carbon-supported Ru catalysts have been prepared by impregnation from aqueous solutions of the precursors. The supports have been pretreated by heating in inert atmosphere at various temperatures, followed by partial oxidation in air at 425 degrees C and then by hydrogen treatment at 900 degrees C. The catalyst samples, diluted 1/22 with quartz powder, have been studied in ammonia synthesis by means of a bench-scale, downflow, continuous, tubular reactor, under standard reaction conditions (430 degrees C, 100 bar total pressure, H-2/N-2 = 1.5/1 feeding ratio). Caesium and Barium proved to be much more effective promoters than Potassium as promoters and the optimal temperature range for support pretreatment was found to be about 1900 degrees C. The ammonia productivity, on a catalyst volume basis, of our best Ru catalyst was about twice higher than that of the most widely used Fe-based commercial catalysts.