Adsorption and catalytic properties of CoxFe3–xO4 spinels. Part 1.—Preparation and characterisation of precursors to ammonia-synthesis catalysts

Abstract

Precipitation and dehydration has produced a series of cobalt–iron oxides Co_xFe_3–xO₄(0 ⩽x⩽ 3) whose surfaces at intermediate x show only marginal iron enrichment and which are useful precursors to ammonia synthesis catalysts. With increasing x activation energies for electrical conduction increase but surface areas estimated by adsorption of N₂, H₂O and n-hexane decrease (and are significantly different for three adsorbates, S_HC < S_N2 < S_H2O, reflecting increasing surface–adsorbate specific interactions). Even for n-hexane enthalpies of adsorption are stronger than expected from mere physical adsorption.