AN INSITU MOSSBAUER SPECTROSCOPIC INVESTIGATION OF THE HYDROGEN PRETREATMENT OF TITANIA-SUPPORTED IRON-IRIDIUM CATALYSTS

The effects of pretreatment in hydrogen of some titania-supported iron-iridium catalysts have been examined in situ by57Fe Mössbauer spectroscopy. The Fe3+ in the supported phase which is formed during the initial preparation of the catalyst in air undergoes partial reduction to Fe2+ when treated in hydrogen at low temperatures. Further treatment in hydrogen at moderate temperatures results in some of the Fe2+ being oxidised to Fe3+ which, on further exposure to hydrogen at elevated temperatures, is predominantly reduced to Fe0 in an iron-iridium alloy. The extent of the anaerobic oxidation is optimised in materials with an iron: noble metal mole ratio of ca. 1:2.5 when supported on high surface area titania by a preparation involving slow initial drying of the catalyst in air at low temperatures and subsequent treatment in hydrogen at ca. 400°C. The results are associated with metal-metal and metal-support interactions which result from the preparative procedure. © 1990 J.C. Baltzer A.G. Scientific Publishing Company.