EFFECT OF PRELIMINARY HEATING ON THE ACTIVATION OF MODEL IRON CATALYST FOR AMMONIA-SYNTHESIS .1. MOSSBAUER STUDIES OF THE CATALYST REDUCTION

The oxidized form of a model, fused iron catalyst for ammonia synthesi s, containing large amounts of wustite (ca. 40 wt.-%), was activated b y reduction. The reduction of catalyst samples with different thermal history and different grain size was continuously monitored by thermog ravimetry as well as periodically by Mossbauer spectrometry. Prior to the reduction, the samples were annealed in nitrogen atmosphere, The l onger the time of primary annealing was, the faster was the reduction process. Some conclusions could be drawn about the nature of the accel eration - the induction period seemed to be shorter, whereas the reduc tion mechanism seemed to remain unchanged, The wustite phase dispropor tionates during the initial annealing, forming metallic iron and magne tite as the final products. Magnetite originating from the decompositi on of wustite showed a faster reduction rate than the primary magnetit e.