Sulfidation mechanism by molybdenum catalysts supported on silica/silicon(100) model support studied by surface spectroscopy

Abstract

The sulfidation of disk-shaped MOO, particles with a thickness of 5-10 nm supported on a 5-nm-thick layer of Si02 on Si(100) in a mixture of 10% H2S in H2 at atmospheric pressure has been studied as a function of temperature. XPS and SIMS indicate the formation of Mo4+OS, at the surface and Mo(1V) oxides (probably H1.6Mo03 or MOO?) in the interior of the particles at temperatures between 20 and 100 OC, whereas MoS2 forms at temperatures of 125 OC and higher. Sulfur is present in two forms, as S2-and in a second form which is most probably Sz2-or SH-, but not elemental sulfur. The additional sulfur species disappear at temperatures between 150 and 200 OC. Rutherford backscattering analysis indicates S:Moatomicratios of 1-1.5 at sulfidation temperatures below 100 OC and of 2-2.5 above 100 OC. It is concluded that the sulfidation of Moo3 to MoS2 proceeds through a Mo(1V) oxysulfide, formed initially at the outside of the particle, and Mo(1V) oxide in the interior of the particle. Sulfidic species are believed to facilitate the reduction of Moo3 to Mo(1V) species at low temperatures.

NaY-Supported Molybdenum Sulfide Catalysts

“…The sulfidation picture emerging from the TPS results obtained for Mo(5.4)/NaY is approximately the same as that described by others for Mo/Al 2 O 3 (22,23), Mo/carbon (33,34), and Mo/SiO 2 (33,35,36) catalysts: (i) Already at room temperature some sulfidation is observed (some irreversible H 2 S uptake and a color change from white to brownish). (ii) At increasing temperatures the sulfidation proceeds via O-S exchange on Mo 6+ (strong H 2 S and zero …”

Surface Science Model of a Working Cobalt-Promoted Molybdenum Sulfide Hydrodesulfurization Catalyst: Characterization and Reactivity

“…At 450 K the majority of the Mo is transformed to a species with a binding energy of 229.2 eV, which indicates that Mo is mostly in an (oxy)sulfidic form. For a detailed description of the changes in Mo XPS spectra during sulfidation we refer to earlier XPS studies of MoO x /SiO 2 /Si(100) model catalysts 15,16 and of crystalline MoO 3 powders. 17 The important point to note from Figure 1 is that sulfidation of Mo takes place between 350 and 450 K, while at 400 K the larger part of the Mo has already been converted to the sulfided state.…”

Application of ¹²⁹Xe NMR Spectroscopy to Analysis of Co-Mo/Al₂O₃ Hydrodesulfurization Catalyst —Effect of Sulfidation on ¹²⁹Xe NMR Spectra—

“…These findings indicate that molybdenum was mostly transformed into Mo 4+ species such as MoS2 13) . As before sulfi dation, the Mo 3d peak shape of the sulfi ded Co _ Mo/Al2O3 was little different from that of the sulfided Mo/Al2O3.…”