Evidence for bulk-phase nitrogen dissolution in iron in catalytic ammonia synthesis

Experiments were carried out in which the reactants, nitrogen and hydrogen were admitted to a fixed bed of triply-promoted iron catalyst in the form of concentration step-functions. Temperature was about 400°C, and total pressure was 2.38 MPs. The bed was stabilized with equimolal flows of hydrogen and nitrogen and then stepped up to pure hydrogen or down to pure nitrogen. From the rate of ammonia production, catalyst properties, and bed temperature behaviour, it was inferred that nitrogen is dissolved by the bulk phase of the iron catalyst. This result has important implications for a general model of transient and forced cyclic operation of catalyst beds.