(638d) Aldehyde Hydrogenation Over Fe, Cu, and Co Sites of Controlled Dispersion On Alkali-Modified Oxide Supports

Supported metal oxides are known to be active hydrogenation catalysts whose efficiency and selectivity can be controlled by the level of dispersion of the metal phase. Here we describe a simple route to supported Fe(III), Co(II), and Cu(II) catalysts of controlled dispersion. Well-defined active sites are prepared by incipient wetness impregnation of aqueous EDTA complexes of Fe, Cu, and Co on neat and alkali-modified SiO₂. Impregnation and drying is followed by mild heat treatment under O₂ to remove the EDTA ligand, which, depending on the support and alkali, can leave highly dispersed metal oxides or small clusters. The catalysts are characterized by H₂-TPR, XANES and diffuse reflectance UV-visible spectroscopy (DRS) and compared to the corresponding exchanged zeolites and impregnation with more typical precursors. In one example, DRS results of these catalysts are characteristic of isolated Fe³⁺ cations up to 0.9 Fe/nm², greatly exceeding that of typical precursors. Additionally, H₂-TPR and XANES show the Fe(III) to Fe(II) transition expected of highly dispersed Fe³⁺ species and no evidence of bulk iron oxides. Finally, the activity, selectivity, and kinetic behavior of the catalysts are studied for crotonaldehyde hydrogenation with dilute H₂.