PREPARATION AND CHARACTERIZATION OF CHLORINE-FREE RUTHENIUM CATALYSTS AND THE PROMOTER EFFECT IN AMMONIA-SYNTHESIS .2. A LANTHANIDE OXIDE-PROMOTED RU/AL2O3 CATALYST

La(NO3)3, Ce(NO3)3, and Sm(NO3)3 were proved to be more effective promoters of ammonia synthesis than CsNO3 when they were applied to a chlorine-free Ru/Al2O3 catalyst. Small amounts of lanthanide nitrates (M/Ru = 1) were as effective as a much greater amount of CsNO3 (CS/RU = 10) for 2 wt% Ru/Al2O3. A chemisorption study disclosed that a smaller amount of lanthanide oxide could cover the Ru surface, whereas much more cesium oxide was necessary to cover the Ru surface. Lanthanide oxide was suggested to have a stronger interaction with the Ru surface than Cs2O and/or CsOH, which are strongly basic and have a greater interaction with the Al2O3 Surface. A model of promoter action is proposed. The apparent activation energies of this reaction were lower (11 to 15 kcal mol-1) than those using a Cs+ promoter (24 kcal mol-1) under 101 kPa of N2 + 3H2. © 1992.