XAFS Characterization of Pt–Mo Bimetallic Catalysts for CO Hydrogenation

doi:10.1006/jcat.1997.1578

Journal of Catalysis

Volume 167, Issue 2, 15 April 1997, Pages 364-371

https://doi.org/10.1006/jcat.1997.1578 Get rights and content

Abstract

Molybdenum–platinum bimetallic catalysts supported on alumina exhibited high activities in CO hydrogenation than supported monometallic catalysts of Mo or Pt. The structure of Mo–Pt bimetallic catalysts, which were prepared by incipient wetness impregnation of γ-alumina with the variation of the order of Mo and Pt addition, was studied by XAFS and CO chemisorption. Since molybdenum contains overlapping contribution of the first and the second shells, EXAFS of these two shells and the first shell of platinum was analyzed for the bimetallic catalysts. EXAFS showed equivocally the formation of bimetallic bonds between Mo and Pt for all bimetallic catalysts. For all bimetallic catalysts, molybdenum seemed to segregate to the surface irrespective of the sequence of the impregnation. Strong interaction of Mo atoms with the support was also identified with EXAFS and XANES for both monometallic Mo catalysts and bimetallic catalysts. Regarding the activities of CO hydrogenation, it was concluded that reduced Mo sites were responsible for the high activity and that Pt helped Mo sites become more reduced.

References (29)

Y.I. Yermakov et al.
J. Catal.
(1976)
T.M. Tri et al.
J. Catal.
(1983)
T.M. Tri et al.
J. Catal.
(1984)
G. Leclercq et al.
J. Mol. Catal.
(1984)
J.C.J. Bart
Adv. Catal.
(1986)
J.S. Lee et al.
Appl. Catal. B
(1996)
P. Lagarde et al.
J. Catal.
(1983)
S.N. Khanna et al.
Surf. Sci.
(1983)
J.S. Lee et al.
J. Catal.
(1990)
J.S. Lee et al.
Catal. Lett.
(1993)

M.A. Vannice

J. Catal.

(1975)

M. Saito et al.

J. Catal.

(1980)

J.S. Lee et al.

J. Mol. Catal.

(1990)

J.J. Rehr et al.

J. Am. Chem. Soc.

(1991)

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Regular ArticleXAFS Characterization of Pt–Mo Bimetallic Catalysts for CO Hydrogenation

Abstract

J. Catal.

J. Catal.

J. Catal.

J. Mol. Catal.

Adv. Catal.

Appl. Catal. B

J. Catal.

Surf. Sci.

J. Catal.

Catal. Lett.

J. Catal.

J. Catal.

J. Mol. Catal.

J. Am. Chem. Soc.

Regular Article
XAFS Characterization of Pt–Mo Bimetallic Catalysts for CO Hydrogenation