EXAFS investigation of structural changes induces during the pretreatment of a titania-supported iron–ruthenium catalyst

Abstract

The localised structural changes which are induced in a titania-supported iron–ruthenium catalysts following treatment in hydrogen have been examine in situ by EXAFS. The ruthenium K-edge EXAFS showed that the initial exposure of the catalyst to hydrogen at 130 °C induced the partial reduction of ruthenium dioxide to ruthenium metal. Subsequent treatment with hydrogen at temperatuer exceeding 500 °C resulted in complete reduction to ruthenium metal. The iron K-edge EXAFS recorded from the material heated in hydrogen at 130 °C complemented the ⁵⁷Fe Möossbauer coexist with Fe³⁺ in a structure related to that of both α-Fe₂O₃ and Fe₃O₄. The iron K-edge EXAFS data recorded from the material treated at 500 °C in hydrogen indicated that Fe³⁺, which was shown by ⁵⁷Fe Möossbauer spectroscopy to result in ca. 67 % reduction of the total iron content to Fe°, gave a material from which the iron K-edge EXAFS showed the presence of both oxygen and ruthenium. NO evidence was found in the ruthenium K-edges EXAFS for the the occurrence of ruthenium–iron scattering. The results suggest that the iron component of the catalyst formed by treatment in hydrogen at 700 °C is highly dispersed on the titania and is coordinated to the oxygen atoms of the support. The ruthenium component of the reduced catalyst, which the ruthenium Ki-edge EXAFS showed to be present as ca. 20 Å metallic clusters, may be envisaged as being anchored to the supportvia iron–ruthenium bonds.