Stability Studies of Highly Active Cobalt Catalyst for the Ammonia Synthesis Process

Abstract

Ammonia is currently considered a promising compound for the chemical storage of hydrogen and as an energy carrier. However, large-scale ammonia production is not possible without an active and stable catalyst enabling efficient, long-term work without the need for its replacement. In this paper, the extended stability studies of the highly active promoted cobalt catalyst for ammonia synthesis were carried out. The long-term activity measurements in NH3 synthesis reaction under conditions close to the industrial ones (400–470 °C, 6.3 MPa, H2/N2 = 3) were compiled with the characterization of catalyst properties on different stages of its work using N2 physisorption, XRPD, STEM-EDX, and H2-TPD. The accelerated aging method was used to simulate the deterioration of catalyst performance during industrial operation. Textural and structural characteristics revealed that the tested catalyst is highly resistant to high temperatures. The lack of significant changes in the specific surface area, morphology of the catalyst particles, surface distribution of elements, and chemisorption properties of cobalt surface during long-term heating (436 h) at 600 °C suggests that stable operation of the catalyst is possible in an ammonia synthesis reactor in the temperature range of 400–470 °C without the risk of losing its beneficial catalytic properties over time. The decline in catalyst activity during the long-term stability test was less than 10%.

Keywords

• ammonia synthesis
• cobalt catalyst
• stability
• catalyst deactivation
• accelerated aging