Adsorption of carbon monoxide on platinum alloys: An infrared investigation

doi:10.1016/0021-9517(84)90088-5

Journal of Catalysis

Volume 90, Issue 1, November 1984, Pages 88-95

https://doi.org/10.1016/0021-9517(84)90088-5 Get rights and content

Abstract

The effect of alloying on the absorption band frequency of CO adsorbed on $Pt, v ̃ (CO Pt)$ , has been investigated with the alloys Pt-Pb, Pt-Sn, and Pt-Re. By use of the isotopic dilution method, it has been established that the downward shift of $v ̃ (CO Pt)$ observed upon alloying Pt with Pb is caused partly by a dilution effect and partly by another, possibly electronic effect. Alloying Pt with Sn or Re, on the other hand, caused only a small shift of $v ̃ (CO Pt)$ , which, moreover, could also be explained at least partly by a dilution effect. Oxidation of the alloy samples resulted in a phase separation of the components; the alloy situation could be restored again by a reduction procedure.

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A vast number of studies have attempted to relate the activity of heterogeneous catalysts to their geometric and electronic structures. The majority of the work elucidating the electronic structure of supported Pt and bimetallic Pt-containing nanoparticles relies on IR spectroscopy of chemisorbed CO [5,14–23]. Changes in the C–O stretching frequency of linearly-adsorbed CO can be used to infer the effect of the support or dopant (alloy metal) on Pt.
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This paper reports a study of PtSn/TiO₂ catalysts reduced at two different temperatures (473 and 773 K) by infrared spectroscopy of CO adsorbed at 298 K and XPS, as well as their behaviour in the vapour phase selective hydrogenation of crotonaldehyde at 333 K. Catalysts with 2 wt% Pt and different Pt:Sn atomic ratios were prepared by co-impregnation of a commercial TiO₂ (P25, from Degussa) with aqueous solutions of H₂PtCl₆ and SnCl₂·2H₂O. XPS results show that tin is in oxidized state when the catalysts are reduced at 473 K, whereas a proportion is in the metallic state after reduction at 773 K. The amount of surface platinum decreases when the tin loading and the reduction temperature increase. The presence of Pt-Sn alloy in the catalysts after reduction at high temperature has been assessed by in situ IR spectroscopy of adsorbed CO, although a proportion of platinum remains in a non-alloyed state. The catalytic activity in the vapour-phase hydrogenation of crotonaldehyde increases after high temperature reduction, and the same behaviour is obtained with selectivity towards the hydrogenation of the carbonyl bond to yield the unsaturated alcohol, the best selectivity being obtained for the catalyst with the lowest Pt/Sn ratio.
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Adsorption of carbon monoxide on platinum alloys: An infrared investigation

Abstract

J. Catal.

J. Catal.

J. Catal.

Acta Metall.

Comput. Coupling Phase Diagrams Thermochem.

J. Catal.

J. Catal.

Surf. Sci.

J. Catal.

C. R. Acad. Sci. Paris

J. Catal.

J. Catal.

J. Catal.