Effect of iron oxide precursor on the properties and ammonia synthesis activity of fused iron catalysts

Triply (Al, Ca and K) promoted wustite-based iron catalyst was prepared and compared with a similarly prepared magnetite catalyst for textural properties and performance in ammonia synthesis. The catalysts were synthesized by fusion method using Fe3O4 and metallic iron with similar nominal loading of promoters in both catalysts. The samples were characterized by N-2 adsorption/desorption, XRD, H-2-TPR, H-2-TPD and EDS-mapping techniques. The Fe2+/Fe3+ ratio in the samples was measured by chemical titration. The stability and activity tests were performed in a fixed-bed reactor under kinetically controlled conditions (T=350-530 degrees C, P=30bar, catalyst loading=1g, feed flow rate=120 Nml/min and H-2/N-2=3/1mol/mol). The catalysts exhibited different distribution of the promoters. Catalytic test results for ammonia synthesis showed that the activity of the wustite catalyst was higher than that of magnetite catalyst under the same reaction conditions. The former was also more readily activated by H-2-reduction. The wustite catalyst showed similar thermostability and mechanical strength as the magnetite catalyst. The ammonia synthesis reaction was not intra-particle diffusion limited on either catalyst. The favorable properties of wustite-based catalysts can be employed to reduce the energy consumption and related emissions of ammonia plants significantly.