Physical characterization of [formula omitted] model supported catalysts : II. Electron spectroscopic studies of reduction behavior

Abstract

X-Ray photoelectron spectroscopy (XPS) and conversion electron Mössbauer spectroscopy (CEMS) have been used to characterize Fe TiO 2 model supported catalysts following hydrogen reductions at progressively higher temperatures. Reduction at temperatures near 707 K converted the initially present Fe 3+ and Fe 2+ into metallic iron. After further treatment at 773 K, the metallic iron peaks in the Mössbauer spectrum were observed to broaden, consistent with the spreading of iron crystallites over the support. Upon reduction at temperatures of ca. 875 K or higher, decreases were seen in the XPS and CEMS spectral iron areas. In addition, CEMS indicated the formation of a new, metallic species that did not show magnetic hyperfine splitting at room temperature, and XPS indicated that part of the Ti 4+ was reduced to lower valence states. These results suggest that hydrogen treatment at these temperatures leads to a reduction of the support and to the diffusion of iron into the support, as a dispersed and strongly interacting species (e.g., γ-Fe; Fe x Ti, 1 ≲ x ≲ 2).