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Investigations of $Cu-Ni/SiO_2$, $Ni-Fe/SiO_2$, $Cu-Fe/SiO_2$ and $Ru-Fe/SiO_2$, bimetallic catalysts by employing EXAFS, Mossbauer and infrared spectroscopies

Kulkarni, GU and Kanna, KR and Arunarkavalli, T and Rao, CNR (1993) Investigations of $Cu-Ni/SiO_2$, $Ni-Fe/SiO_2$, $Cu-Fe/SiO_2$ and $Ru-Fe/SiO_2$, bimetallic catalysts by employing EXAFS, Mossbauer and infrared spectroscopies. In: Advances in Catalyst Design, 1993, pp. 373-400.

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Abstract

In monometallic $Fe/SiO_2$ and $Ni/SiO_2$ catalysts, the transition element undergoes only partial reduction to the metallic state on treatment with hydrogen, unlike in $Cu/SiO_2$ where the reduction is complete. CO adsorption measurements on these catalysts, show that there is hardly any adsorption on the $Fe/SiO_2$ catalyst whereas both bridged and linear CO species are seen on the surfaces of $Ni/SiO_2$ and $Cu/SiO_2$ catalysts. In-situ Moessbauer and EXAFS investigations of $Fe-Ni/SiO_2$ catalysts with different Fe/Ni ratios show that the reducibility of both Fe and Ni is greater in the bimetallic catalysts than the corresponding monometallic catalysts. Reduced bimetallic catalysts show evidence for the formation of fcc. or bcc. alloy phases that are superparamagnetic or ferromagnetic depending on the components. In the case of $Fe-Cu/SiO_2$, the promotion effect of Cu on the reduction of Fe is marginal and alloy formation is observed mainly in Fe-rich compounds. Alloy formation and the reducibility of Ni in $Cu-Ni/SiO_2$ catalysts increase with increasing Cu content. Clearly, mutual promotion of the reducibility of the transition metals is related to the extent of alloy formation between them. When a noble metal is present, like in $Fe-Ru/SiO_2$, both hydrogen spillover and FeRu alloy formation bring about reduction of Fe. In-situ FT- IR investigations of CO adsorption on the bimetallic catalysts show variations in the relative intensities of bridged and linear CO species with the components which in turn may be related to the reactivity of the catalyst surface.

Item Type: Conference Paper
Additional Information: Copyright of this article belongs to World Scientific.
Department/Centre: Division of Chemical Sciences > Solid State & Structural Chemistry Unit
Date Deposited: 04 Jul 2008
Last Modified: 27 Aug 2008 13:30
URI: http://eprints.iisc.ernet.in/id/eprint/14615

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