Preparation and properties of iron oxide and metallic iron catalysts.

Abstract

After an introduction dealing with the applications of iron oxide and metallic iron catalysts, the preparation of iron (oxide) catalysts is discussed. The aqueous chemistry of iron(III) and iron (II) is surveyed as well as two reactions where the extent of hydration of the iron oxide is important, viz. the removal of hydrogen sulfide and the oxidation of carbon monoxide. The activity of iron oxide in the carbon monoxide shift conversion is subsequently considered. It is argued that the reduction of (supported) iron oxide is governed by the transport of water vapor out of the pores of the system being reduced. Especially with iron oxide supported on highly porous carriers the transport of water out of the system and thus the reduction is difficult. Interaction with the support causes the reduction to proceed through an intermediate iron(II) oxide phase. Experiments on single crystals have shown that a monolayer of oxygen on the Fe(100) surface is very stable and almost impossible to remove by reduction with hydrogen. Oxygen present on the closely packed Fe(110) surface, on the other hand, is easily removed by reaction with hydrogen. The implications for the determination of iron surface areas by hydrogen adsorption and the ammonia synthesis are discussed.