Promotion effect of lanthanum on the Co/La/Ba ammonia synthesis catalysts—the influence of lanthanum content

Abstract

The effect of lanthanum content on catalytic properties of cobalt catalysts for ammonia synthesis has been studied. The amount of La in the studied catalysts ranged from 0 to 55.7wt.%, whereas the barium content was constant (approx. 1.5mmolgCo−1). The characterization studies included a determination of properties of the catalysts precursors (N2 physisorption, XRPD), as well as the catalysts in the active form (TPR-MS, XRPD, SEM-EDX and H2 chemisorption). The activity of the obtained Co/La/Ba catalysts in NH3 synthesis was tested in a flow differential reactor operating under conditions close to the industrial ones (p=6.3MPa, T=400°C, H2/N2=3:1). It has been found that lanthanum plays the role of an effective structural promoter. However, there is a strong correlation between the La content in the catalysts and their properties: increasing amount of lanthanum is accompanied by the improvement in textural properties of both the precursors and catalysts in the reduced form. Lanthanum does not work as an activator for the cobalt surface. The increase in the activity of Co/La/Ba catalysts was observed as a result of a development of the active phase surface by increasing the La content.