A surface spectroscopic study of Coz.sbnd;MoAl2O3 catalysts using ESCA, ISS, XRD, and Raman spectroscopy, I

Abstract Laser Raman spectroscopy, X-ray photoelectron spectroscopy, low-energy ion-scattering spectroscopy, and X-ray diffraction have been used to characterize a series of Coz.sbnd;Mo Al 2 O 3 catalysts containing 15 wt% MoO 3 and 0 to 8 wt% CoO in their oxide, reduced, and sulfided forms. These data show that the catalyst surface contains CoMoO 4 and irreducible Co 2+ ions of tetrahedral symmetry when the CoO concentration is 0 to 6%. With 7 to 8% CoO, additional surface species includes Co 3 O 4 crystallites on the γ-Al 2 O 3 surface. Formation of Co 3 O 4 coincides with an increased Mo reducibility and a decreased BET surface area. These results are compared to previously published data on Coz.sbnd;Mo Al 2 O 3 and suggest that the state of dehydration-dehydroxylation of the Al 2 O 3 surface before impregnation of Co and Mo affects their subsequent speciation. Autoclave studies investigating the hydrodesulfurization (HDS) and hydroconversion of coal using these catalysts are also reported. Significance of the surface speciation with respect to these activity studies is discussed.