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Properties of Pure and Sulfided NiMoO4 and CoMoO4 Catalysts: Tpr, Xanes and Time-Resolved XRD Studdzs

Published online by Cambridge University Press:  10 February 2011

S. Chaturvedi ,
J. A. Rodriguez ,
J. C. Hanson ,
A. Albornoz  and
J. L. Brito
S. Chaturvedi
Affiliation:
Chemistry Department, Brookhaven National Laboratory, Upton, NY 11973, USA
J. A. Rodriguez*
Affiliation:
Chemistry Department, Brookhaven National Laboratory, Upton, NY 11973, USA
J. C. Hanson
Affiliation:
Chemistry Department, Brookhaven National Laboratory, Upton, NY 11973, USA
A. Albornoz
Affiliation:
Centro de Quimica, IVIC, Caracas 1020-A, Venezuela
J. L. Brito*
Affiliation:
Centro de Quimica, IVIC, Caracas 1020-A, Venezuela
*
(1)Authors to whom correspondence should be addressed
(1)Authors to whom correspondence should be addressed
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Abstract

X-ray absorption near-edge spectroscopy (XANES) was used to characterize the structural and electronic properties of a series of cobalt- and nickel-molybdate catalysts (AMoO4.nH20, α-AMoO4, β-AMoO4; A= Co or Ni). The results of XANES indicate that the Co and Ni atoms are in octahedral sites in all these compounds, while the coordination of Mo varies from octahedral in the a-phases to tetrahedral in the β-phases and hydrate. Time-resolved x-ray diffraction shows a direct transformation of the hydrates into the β-AMoO4 compounds (following a kinetics of first order) at temperatures between 200 and 350 °C. This is facilitated by the similarities that the AMoO4.nH20 and β-AMoO4 compounds have in their structural and electronic properties. The molybdates react with H 2 at temperatures between 400 and 600 °C, forming gaseous water and oxides in which the oxidation state of Co and Ni remains +2 while that of Mo is reduced to +5 or +4. After exposing α-NiMoO4 and P-NiMoO4 to H2S, both metals get sulfided and a NiMoSx phase is formed. For the β phase of NiMoO4 the sulfidation of Mo is more extensive than for the a phase, making the former a better precursor for catalysts of hydrodesulfurization reactions.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 497: Symposium Z – Recent Advances in Catalytic Materials , 1997 , 41
Copyright
Copyright © Materials Research Society 1998

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References

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