Catalytic functionalities of supported sulfides: II. Effect of support on Mo dispersion

doi:10.1016/0021-9517(84)90109-X

Journal of Catalysis

Volume 85, Issue 1, January 1984, Pages 53-62

https://doi.org/10.1016/0021-9517(84)90109-X Get rights and content

Abstract

Several Mo and CoMo catalysts on different supports, previously evaluated for thiophene hydrodesulfurization (HDS) and 1-hexene hydrogenation (HYD) activities, were characterized for Mo dispersion in the catalysts. Techniques employed for characterization included XRD, ESCA, and O₂ chemisorption of catalysts, and determination of “active OH” on supports. For the calcined (oxide) form of Mo and CoMo catalysts on Al₂O₃, several SiO₂Al₂O₃ compositions, and SiO₂, it was found that essentially monolayer dispersion of the Mo was present on Al₂O₃ and low SiO₃-containing supports, whereas in the case of high SiO₂-containing and SiO₂ supports evidence was found for three-dimensional crystallites for the Mo phase. The sulfided form of these catalysts gave essentially the same results. These findings are interpreted in terms of the degree of interaction of the Mo phase with the support. To account for changes in HDS and HYD activities of the catalysts, it is proposed that HDS occurs at vacancies on corner sites and HYD at vacancies on edge sites of the MoS₂ phase present.

References (27)

G. Muralidhar et al.
J. Catal.
(1984)
N. Yamagata et al.
J. Catal.
(1977)
Y. Okamoto et al.
J. Catal.
(1980)
C. Defosse
J. Electron Spectrosc. Relat. Phenom.
(1981)
P. Gajardo et al.
J. Catal.
(1980)
K.S. Chung et al.
J. Catal.
(1980)
N. Topsøe
J. Catal.
(1980)
G.C. Stevens et al.
J. Less-Common Met.
(1977)
G.A. Somorjai
R. Candia et al.
J. Cat.
(1982)

J.H. Scofield

J. Electron Spectrosc. Relat. Phenom.

(1976)

D.R. Penn

J. Electron Spectrosc. Relt. Phenom.

(1976)

F. Lepage et al.

C.R. Acad. Sci. Paris Ser. C

(1975)

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Citation Excerpt :
The observed behavior is related to a higher density of sulfides of molybdenum and tungsten formed on the surface of the catalyst in the more active catalysts, as established by the results of X-ray diffraction, in which corresponding peaks are more intense for samples with higher catalytic activity and this is confirmed with the diffuse reflectance spectroscopy results, in which the more active catalysts contain a greater quantity of tetrahedral and octahedral molybdenum and tungsten species (derived from the higher area for both deconvoluted spectral bands), being known that an increase in octahedral species of these metals improves catalytic activity. It has also found in all samples the presence of oxide precursors with cobalt ions with octahedral coordination, which are beneficial in the formation of active sites for catalysis of reactions of hydrodesulfurization [54,56–62]. Additionally, the results of Micro Raman spectroscopy indicates the presence of molybdenum and tungsten species in octahedral coordination in all samples, showing a greater intensity of the bands related with this species the samples prepared by mechanical mixing of pure silicas, which is related with the fact that these catalysts contain the highest number of Mo(W)O terminal bonds, which has been reported as responsible of the catalytic activity in the hydrodesulfurization of dibenzothiophene [54].
A group of hydrodesulfurization (HDS) catalysts, based on transition metal sulfides (Co-Mo-W) and supported on mechanically-mixed mesoporous silicas (SBA-15 and SBA-16), have been synthesized and characterized by physicochemical methods (DRS-UV–vis, Micro Raman spectroscopy, XRD, SEM, HRTEM, EDS and catalytic activity). It has been demonstrated that the use of a mixture of silicas with two different porous structures has an advantage with respect to the use of the SBA-15 and SBA-16 separately for the preparation of supported catalysts for hydrodesulfurization reactions of refractory sulfur compounds, such as dibenzothiophene. This is because the presence of different porous structures has a positive effect over the diffusion processes of the precursors of the active phases on the support, and the whole result is a higher catalytic activity for the HDS reactions of dibenzothiophene, even more than that of the commercial catalyst used as a comparative model; this activity is also related with the stage of the synthesis process in which the mixture is done.

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¹: Research Associate, 1980–1982.

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Catalytic functionalities of supported sulfides: II. Effect of support on Mo dispersion

Abstract

J. Catal.

J. Catal.

J. Catal.

J. Electron Spectrosc. Relat. Phenom.

J. Catal.

J. Catal.

J. Catal.

J. Less-Common Met.

J. Cat.

J. Electron Spectrosc. Relat. Phenom.

J. Electron Spectrosc. Relt. Phenom.

C.R. Acad. Sci. Paris Ser. C