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

Abstract

The effect of sulfi dation on 129 Xe NMR spectra of Co _ Mo/Al2O3 hydrodesulfurization catalysts was investigated. Before sulfidation, catalysts containing cobalt such as Co/Al2O3 and Co _ Mo/Al2O3 showed remarkable 129 Xe NMR peak broadening, whereas one sharp 129 Xe NMR peak was observed for Mo/Al2O3 and Al2O3, mainly caused by the paramagnetic effect of cobalt oxides such as CoAl2O4 and CoO. In contrast, after sulfi dation, the remarkable broadening of the 129 Xe NMR peak did not occur. We consider that the paramagnetic effect of cobalt was much reduced due to the transformation of paramagnetic oxides such as CoAl2O4 and CoO into antiferromagnetic sulfi des such as the Co _ Mo _ S phase and Co9S8. In addition, XPS of the sulfi ded catalysts showed that the Co 2p binding energy of the sharp peak for Co _ Mo/Al2O3 was 0.7 eV higher than that for Co/Al2O3. This result strongly suggests that cobalt was mainly present as the Co _ Mo _ S phase on the surface and is closely related to the observation that the 129 Xe NMR peak of sulfi ded Co _ Mo/Al2O3 was shifted further downfi eld in comparison with sulfi ded Mo/Al2O3. 129Xe NMR spectroscopy is sensitive to the formation of the Co _ Mo _ S phase on Co _ Mo/ Al2O3 hydrodesulfurization catalyst.

In Situ Imaging and Computational Modeling Reveal That Thiophene Complexation with Co(II)porphyrin/Graphite Is Highly Cooperative

“…19,26 Particular attention has been focused on in situ HDS studies monitoring the reaction of thiophenes with molybdenum, tungsten, and rhenium with Co, Mg, or Ni promoters adsorbed on metal oxides (Al 2 O 3 , SiO 2 ) and graphite. 9,27−30 thiophene adsorption, and reaction dynamics employed Xray, 31 IR, 32,33 nuclear magnetic resonance (NMR), 34,35 and DFT methods. 36,37 Proposed thiophene binding modes to the different metal centers on the surface included η 1 (S) and η 5 (C�C) coordination.…”

“…Current keen interest in thiophene reactive adsorption to metal complexes supported on surfaces is limited by a dearth of information about the local structure of the molecules under reaction conditions. To date, studies of thiophene binding to transition metal complexes supported on solid substrates have been limited (vide infra). , Particular attention has been focused on in situ HDS studies monitoring the reaction of thiophenes with molybdenum, tungsten, and rhenium with Co, Mg, or Ni promoters adsorbed on metal oxides (Al 2 O 3 , SiO 2 ) and graphite. ,− Studies involving catalyst characterization, thiophene adsorption, and reaction dynamics employed X-ray, IR, , nuclear magnetic resonance (NMR), , and DFT methods. , Proposed thiophene binding modes to the different metal centers on the surface included η 1 (S) and η 5 (CC) coordination . However, because the catalyst surface is complex, the mode(s) of thiophene absorption and reaction dynamics are still not well established.…”