REMOVAL OF CHLORINE IONS FROM RU/MGO CATALYSTS FOR AMMONIA-SYNTHESIS

The effects of the removal of chlorine and the KNO3 promoter were studied on RuCl3 precursor/MgO catalysts for ammonia synthesis. Chlorine ions were decreased by increasing the temperature of reduction by hydrogen; however, chlorine still remained even after a reduction at 973 K. Both hydrogen adsorption and ammonia synthesis activity increased when increasing the reduction temperature up to 923 K which suggested that chlorine ions were removed from the ruthenium surface. Most of the chlorine ions were thought to be located on MgO (base); however, a small amount was thought to be located on the ruthenium metal surface as RuCl3 at low temperature (< 773 K) or as MgCl2 at high-temperature reduction (> 773 K). When the RuCl3/MgO catalyst was impregnated with the promoter (KNO3) and reduced, it became effective at a K/Ru mole ratio higher than three. This suggests that potassium reacts with chlorine ions before or during hydrogen reduction, and then acts as an electron donor to the ruthenium surface. On the other hand, when the Ru/MgO catalyst is reduced with hydrogen at 773 K, then impregnated with the promoter and treated with hydrogen, KNO3 becomes effective even at a K/Ru mole ratio as low as 0.3. The potassium ions were thought to promote the ruthenium surface instead of accepting the chlorine ions in this case.