Promoting effect of fluorine on cobalt—molybdenum/ titania hydrodesulfurization catalysts (original) (raw)
Related papers
The Role of Titania Support in Mo-Based Hydrodesulfurization Catalysts
Journal of Catalysis, 1999
has been prepared to study the role of titania in Mo-based HDS catalysts. The catalysts were tested in the thiophene hydrodesulfurization reaction at atmospheric pressure and were characterized by UV-vis diffuse reflectance spectroscopy (DRS), TPR-S (after reaction), and highresolution electron microscopy (HREM). The results show that the titanium species formed during sulfidation and HDS reaction act as promoter of the Mo phase giving rise to a synergy effect. This synergy effect seems to be related to the electronic properties of the partially reduced and/or sulfided TiO 2 surface and, in particular, to the presence of Ti 3+ ions. Finally, estimation of the number of sulfur vacancies created on the used catalysts during TPR-S indicate that only a small proportion of all the edge/corner Mo atoms present in the MoS 2 crystallites, estimated from HREM observations, are active in HDS and that a low number of sulfur vacancies are required. )) × 100 = 0, 20, 50, 80, 90, and 100%) were prepared from appropriate amounts of each previously calcined 59
Support effect on the properties of iron–molybdenum hydrodesulfurization catalysts
Catalysis Letters, 2006
Two series of Mo and Fe containing catalysts have been prepared over alumina and titania supports using H 3 PMo 12 O 40 heteropolyacid (HPMo) and Fe salt of HPMo. Catalysts have been characterized by BET, SEM, IR, TPR, XPS methods and by their HDS activity in the reaction of thiophene conversion. The TiO 2 -supported catalysts with low Mo concentration (6 wt%) show higher HDS activity than the catalyst with 12 wt% Mo. Iron promoting effect (Fe/Mo $ 0.1) is observed with both, the aluminaand titania-supported catalysts. Iron supported over alumina increases Mo reducibility and decreases it on TiO 2 -supported catalysts. Compared to alumina-supported catalysts, the TiO 2 -supported catalysts show higher surface concentration of Mo 6+ and Mo 5+ in octahedral coordination -Mo(Oh). Iron increases the Mo(Oh) concentration even more. After sulfidation the Fe-containing catalysts show formation of different Mo valence states (Mo 4+ , Mo 5+ , Mo 6+ ), Fe-P, Mo-P and/or Fe-Mo-P bonds, which affect the HDS catalytic activity.
TiO2-supported iron–molybdenum hydrodesulfurization catalysts
Applied Catalysis A: General, 2005
TiO 2 -supported Mo (6 and 12 wt.%) and Fe (0.25-1.0 wt.%) containing catalysts have been prepared using H 3 PMo 12 O 40 heteropolyacid (HPMo) and Fe salt of HPMo. Catalysts have been characterized by BET, SEM, IR, TPR, XPS methods and by their HDS activity in the reaction of thiophene conversion. Promoting effect of TiO 2 on Mo catalysts was confirmed, higher in case of catalysts with low Mo concentration (6 wt.%) than in case of the catalyst with 12 wt.% Mo. The highest HDS activity and stability was observed after introducing Fe in the form of HPMo countercation (Fe/Mo $ 0.1). Iron increases concentration of Mo 6+ and Mo 5+ in octahedral coordination. After sulfidation, the Fe-containing catalysts show presence of different Mo valence states (Mo 4+ , Mo 5+ , Mo 6+ ), Fe-P, Mo-P and/or Fe-Mo-P bonds that affect the HDS catalytic activity. #
Journal of the Japan Petroleum Institute, 2005
Mo catalysts were prepared by impregnation of titania synthesized by the pH swing method which provides a TiO2 carrier with a high specific surface area (134 m 2 g −1) and excellent mechanical properties. Dibenzothiophene (DBT) hydrodesulfurization (HDS) activity was estimated over the obtained catalysts under typical HDS reaction conditions for various Mo contents. The activity increased linearly with Mo content up to ca. 16 wt% MoO3 and then decreased for higher Mo loadings. The sulfur behavior on the sulfided Mo/TiO2 catalysts was elucidated under the reaction working conditions using a 35 S radioisotope tracer method, or the HDS of 35 S-labeled DBT. The results indicated that at a given temperature the H2S release rate constant (kRE) was almost constant irrespective of the Mo content, and the amount of labile sulfur (S0) increased linearly with the Mo content in parallel with the activity up to ca. 16 wt% MoO3. The optimal Mo dispersion was 5.2 atom/nm 2 , which is higher than the optimal Mo dispersion on 70 m 2 g −1 TiO2 (4.2 atom/nm 2). Comparison of kRE and S0 of the titania-based catalysts and the alumina-based catalysts suggested that the active phase consists of a 'TiMoS' phase exhibiting a promoting effect similar to the well-known 'CoMoS' phase (promotion of the MoS2 active phase by Ti atoms).
Journal of Catalysis, 1997
Activity and product selectivity have been measured for thiophene hydrodesulfurization (HDS) over model silica-supported molybdenum catalysts at a pressure of 1 atm and at temperatures ranging from 398 to 673 K. The model catalysts feature isolated molybdenum atoms in the +2, +4, and +6 oxidation states and molybdenum dimers with each molybdenum atom in the +4 oxidation state. Silica-supported MoS 2 , prepared by deposition and decomposition of (NH 4) 2 MoS 4 , was used for reference. There is a correlation between thiophene HDS activity and molybdenum oxidation state, with Mo(II) most active. Thiophene HDS activity does not show a significant structure dependence for isolated Mo(IV) versus dimeric Mo(IV) catalysts. Activation energies of 51.5 and 49.9 kJ/mol were determined for thiophene HDS over Mo(II) and MoS 2 /SiO 2 catalysts, respectively. Butane and butenes are the major products of thiophene HDS with little butadiene detected. Activity and selectivity trends suggest the HDS reaction is initiated by η l binding of thiophene on the supported metal catalysts.
Applied Catalysis, 1989
The nature of the support effect in unpromoted (MO) and promoted (CO-MO) catalysts was examined by comparing the thiophene hydrodesulphurization activities of the catalysts supported on A1203, TiO, and SiOz-A1z03. Catalyst samples were prepared by the incipient wetness impregnation method and characterized by photoelectron spectroscopy (XPS) and high-resolution electron microscopy (HREM). The activity per atom of molybdenum was higher for the TiO,-unpromoted and-promoted catalysts, but the synergistic effect was higher for the Al*O~-sup~~ catalysts. The absence of a significant shift in the titanium and molybdenum binding energies for catalyst supported on TiOz and A&O5 with respect to unsupported MO& catalyst does not support an electronic effect as the main cause of the great differences in activity between TiOz-and A1,03supported catalysts. The HREM results show clear evidence of the existence of smaller MoSz particles on the TiO~-suppo~d catalysts. Also, the addition of the promoter leads to the formation of smaller particles on the surface of the TiOz-supported catalysts. The differences in activity and synergistic effect for the different catalysts could be explained in terms of different activities for the smaller and larger particles. It is proposed that the difference in activity between the smaller and larger particles is related to the MO& crystallite orientation on the surface of the support.
Applied Catalysis, 1989
The nature of the support effect in unpromoted (MO) and promoted (CO-MO) catalysts was examined by comparing the thiophene hydrodesulphurization activities of the catalysts supported on A1203, TiO, and SiOz-A1z03. Catalyst samples were prepared by the incipient wetness impregnation method and characterized by photoelectron spectroscopy (XPS) and high-resolution electron microscopy (HREM). The activity per atom of molybdenum was higher for the TiO,-unpromoted and -promoted catalysts, but the synergistic effect was higher for the Al*O~-sup~~ catalysts. The absence of a significant shift in the titanium and molybdenum binding energies for catalyst supported on TiOz and A&O5 with respect to unsupported MO& catalyst does not support an electronic effect as the main cause of the great differences in activity between TiOz-and A1,03supported catalysts. The HREM results show clear evidence of the existence of smaller MoSz particles on the TiO~-suppo~d catalysts. Also, the addition of the promoter leads to the formation of smaller particles on the surface of the TiOz-supported catalysts. The differences in activity and synergistic effect for the different catalysts could be explained in terms of different activities for the smaller and larger particles. It is proposed that the difference in activity between the smaller and larger particles is related to the MO& crystallite orientation on the surface of the support. 0166-9834/89/$03.50 0 1989 Elsevier Science Publishers B.V.