The effect of potassium oxide upon the decomposition of ammonia over iron synthetic ammonia catalysts

Abstract

The decomposition of ammonia was carried out in a flow system over three different well-reduced iron synthetic ammonia catalysts (A, with 4.72% alumina, 0.31% potassium oxide and 0.05% silica as promoters; B, with 2.03% alumina, 0.81% potassium oxide and 0.61% silica, and C, with 4.72% alumina, 0.24% potassium oxide and 0.05% silica) at a total pressure of one atmosphere and in the range of 378 to 454 °C. The rate observed was proportional to ( P NH 3 P H 2 1.5) α (α: constant) and the activation energy was found to be in the range of 35.0–50.5 kcal/mol over catalysts (A) and (B). On the other hand, on catalyst (C) the rate was proportional to ( P NH 3 P H 2 0.5) β (β: constant) with the activation energy of 15 kcal/mol. From these results, it was concluded that the decomposition is controlled by the desorption of adsorbed nitrogen over catalysts (A) and (B), whereas with the decreased amount of potassium oxide the dehydrogenation of adsorbed amino NH 2( a) controls the decomposition. In connection with these results, the promoter action upon decomposition was briefly discussed. In addition, it was shown that the kinetics of the decomposition over catalyst (A) was sensitively affected by the reduction conditions of the catalyst.