The effect of cobalt on the activity of iron catalyst supported on magnesium hydroxide carbonate (MHC) in the ammonia synthesis

Abstract

AbstractThe effect of cobalt on the activity of the magnesium hydroxide carbonate supported iron catalysts for ammonia synthesis was studied. The addition of cobalt has been found to increase considerably the activity of the catalyst samples. A sample containing ca 20 wt% Co as metallic phase showed maximum activity in the ammonia synthesis (X‐ray fluorescence (XRFS) was used to analyze the sample compositions). The precursor reduction temperature proved an important factor affecting properties of the samples studied, and catalyst reduced at the relatively high temperature of 873 K was the most active. On the basis of the activity measurements, phase structure studies with the X‐ray diffraction (XRD) method, temperature‐programmed reduction studies, and a Mössbauer spectroscopic investigation, a conclusion has been drawn that the formation of an intermetallic iron‐cobalt compound is crucial to the catalyst activity. It has been postulated that this might be due to the surface restructuring by exposing the most active iron surface, Fe(111). Considering the support and promoter natures the catalysts studied can be called ‘super‐basic’. Negligible potassium addition (0.2 wt% K) in the form of KOH can cause very high increase in the catalytic activity in ammonia synthesis.