The micromorphology of the activated iron catalyst used for ammonia synthesis

Abstract

The internal microstructure of an industrial iron catalyst for ammonia synthesis was investigated using surfaces of electropolished grains of the catalyst which had operated for 240 h in ammonia synthesis under atmospheric pressure. Optical microscopy and SEM/EDX were used to investigate the disposition of several structural motives. The heterogeneity of distribution of the promoter oxides was confirmed to exist on all levels of resolution. The microstructural discrimination of the iron metal into several distinct features and the porous structure of the iron crystals were made visible. An EXAFS experiment on these catalyst particles confirms that all iron structures are made-up from bcc iron unit cells and that the discrimination of the iron species should result from textural rather than from atomic structural differences.