Chemical State Of Iron Research Articles

X-ray photoelectron spectroscopic studies of iron oxide catalysts prepared from the calcination of iron sulfates at high temperature

Surfaces of iron sulfates calcined at various temperatures ranging from 500 to 900 °C were examined by X-ray photoelectron spectroscopy and X-ray diffraction. The sulfates when calcined in air at 700 °C, showed the highest catalytic activity for the Friedel-Crafts benzylation, benzoylation, and isopropylation of toluene, and were found to have the following surface properties: (1) the iron sulfate completely decomposes to form α-Fe 2O 3 at temperatures from 675 to 700 °C. At higher temperatures, the crystalization proceeds rapidly, but any change in the chemical state of iron and oxygen ions on the surface due to the decomposition process can not be deteted. (2) A small amount of sulfur (0.15 wt%) remains as SO 4 on the surface at temperatures greater than 700 °C after decomposition. The conclusion was confirmed by the benzylation with the differently sulfur-treated ferric oxide catalysts.

The chemical state of iron in reduced PdFe/Al2O3 catalysts

Mossbauer spectroscopic studies show that ferric ions in low concentrations (0.05 wt%) on η-Al2O3 are unaffected by hydrogen at room temperature and can only be reduced to the ferrous state at temperatures as high as 700 °C. Ferric ions in PdFeη-Al2O3 catalysts, however, are reduced to the ferrous state at room temperature and to the metallic state at 500 °C with formation of PdFe alloys. The results of this investigation are consistent with a model in which the reduction of iron to the metallic state and formation of PdFe alloys requires contact between a palladium particle and the oxide of iron which is reduced. Hydrogen “spillover” does occur but only across the interfacial contacts between palladium particles and the iron oxide. No evidence was found to support a model, proposed by others, in which ferromagnetic iron metal is formed in reduced PdFeAl2O3 catalysts as a result of the diffusion of hydrogen over the support surface from palladium particles to an oxide of iron.