An investigation of metal-support interactions in some iron, ruthenium and ironȁruthenium catalysts by in situ iron-57 Mössbauer spectroscopy

Abstract

The reduction by hydrogen of alumina- and silica-supported iron catalysts has been studied in situ by iron-57 Mo˝ssbauer spectroscopy. The results from catalysts with loadings of 5% iron show that the stronger metal support interaction between iron and alumina gives rise to small particle iron oxide which is partially reduced in hydrogen to iron(II) whilst silica-supported iron, in which the metal-support interaction is weaker, forms large particle magnetically ordered α-Fe2O3 which is reduced to metallic iron and iron(II). Treatment of these and some alumina- and silica-supported ironȁruthenium catalysts of similar total metal loading in atmospheres of carbon monoxide and hydrogen give Mo˝ssbauer spectra which show that the reducibility of iron depends on both the ruthenium content of the bimetallic catalyst and the character of the support. Such treatment gives rise to the formation of an iron carbide phase in the silica-supported iron catalysts.Alumina- and silica-supported catalysts containing 10% iron, or 5% ruthenium, or 5% iron-5% ruthenium are more active towards carbon monoxide hydrogenation than those with lower iron loadings. The different catalytic properties of these materials, together with the changes induced in the activity and selectivity of alumina- and silica-supported ruthenium by the incorporation of iron, reflect the variation in metal-support interaction as the nature of the metallic phase is altered.