ACTIVITY AND REDUCTION BEHAVIOR OF FUSED IRON CATALYSTS CONTAINING COBALT FOR AMMONIA-SYNTHESIS - A STRUCTURE STUDY

Mossbauer effect spectroscopy (MES) studies of cobalt-containing fused iron catalysts show that different cobalt distributions occur in irre gularly shaped catalysts (formed by natural cooling of the fused mass in air) and in ball-shape catalysts (formed in water by sudden cooling ). The Co2+ ions replace Fe2+ ions in the B sites of the inverse spine l structure of Fe2O4 for the former catalyst, while a relatively even distribution over A and B sites occurs for the latter. The above resul ts are supported by X-ray diffraction (XRD), For the irregular catalys ts, the activity and specific surface area increase to some extent wit h increasing cobalt content and decreasing atomic iron ratios (i.e. Fe 2+/Fe3+). For the ball-shape catalyst, in spite of the somewhat smalle r specific surface area, a higher specific activity results in an over all activity that is incomparable to that of the irregular catalyst; t he pore surface distribution is shifted to larger pores. The reaction rate constant decreases with increasing total pressure, The ball-shape d catalyst follows the relation k(T.P)similar to exp(jp), while the ir regular catalyst is fits the Nielsen equation, k(T.P)similar to p(i), where i and j are small negative numbers. The intrinsic reduction kine tics of the ball-shape catalyst are best in line with the contracting sphere model, and reduction of industrial size catalysts also shows th at cobalt promotes the reduction of the catalyst, On the other hand, t he uneven distribution of Co2+ ions in the irregular catalyst causes i ts intrinsic reduction kinetics to deviate from the contracting sphere model. We consider that the easier reduction of the cobalt containing catalyst may be caused by the much easier reduction of the CoFe2O4 pr esent.