Hydrogenation of carbon monoxide on amorphous Fe81B13.5Si3.5C2. Activity and segregational behaviour of the alloy

Abstract

Amorphous Fe₈₁B_13.5Si_3.5C₂ pretreated at 25, 450 and 500 °C in a hydrogen atmosphere has been tested for the hydrogenation of CO in a flow microreactor at 400 °C. Auger electron spectroscopy, combined with Xe⁺ sputtering and X-ray diffraction line-broadening, showed that the pretreatment at 450 and 500 °C caused simultaneously segregation of the main-group elements B, Si and C onto the surface and growth of the iron particles. Pretreatment at 450 °C led to alloys consisting of crystalline α-iron particles with a mean size of d≈ 25 nm which were imbedded in the amorphous iron matrix; pretreatment at 500 °C resulted in completely crystalline alloys with d > 50 nm. With all alloys the main reaction products of CO hydrogenation were methane, ethylene, propene and carbon dioxide. Both activity and product distribution were found to depend on the iron particle size. The amorphous alloy with d⩽ 20 nm exhibited at 400 °C an activity ca. six times higher than the crystalline alloy with d > 50 nm.