FISCHER-TROPSCH SYNTHESIS OVER FRESHLY REDUCED IRON-RUTHENIUM ALLOYS

Surface analysis of unsupported FeRu alloys was accomplished using x-ray photoelectron spectroscopy (XPS) and secondary ion mass spectrometry (SIMS) after the catalysts were reduced in flowing H2 at 673 K for 4 h in a pretreatment chamber and introduced directly into the UHV instrument without exposure to the air. XPS lines show Fe and Ru to be metallic after reduction. Quantitative analysis of the first several layers using XPS shows enrichment of the surface region in Fe as expected. Analysis of the secondary ion emission as a function of composition shows a marked decrease in the Ru+ emission from 97Ru3Fe compared to the pure Ru catalyst, suggesting alteration of the electronic properties of the surface upon addition of a small amount of Fe. Semiquantitative analysis of the uppermost layer using SIMS suggests greater Fe enrichment in the first layer than the average enrichment calculated from XPS for the first several layers. The initial activity and selectivity of the catalysts for Fischer-Tropsch synthesis were measured at 1 atm and 573 K in 3.3H2 + CO at conversions below 3%. Selectivity to methane decreases through a minimum with increasing Fe content in the first layer. High propylene and ethylene yields were found for the alloy catalysts. A marked increase in the selectivity of the catalysts to propylene and, particularly, ethylene for 3Fe97Ru compared to pure Ru correlates with the sharp changes in SIMS yields. © 1979.