Copper ion substituted hercynite (Cu sub(0.03)Fe sub(0.97)Al sub(2)O sub(4)): A highly active catalyst for liquid phase oxidation of cyclohexane

Copper ion substituted MAl sub(2)O sub(4) (M = Mg, Mn, Fe, Ni and Zn) spinels, Cu sub(x)M sub(1-x)Al sub(2)O sub(4)(x = 0.03 and 0.05), have been synthesized by a single step solution combustion method. Of the various compositions studied the 3 at.% copper ion substituted hercynite, Cu sub(0.03)Fe s...

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Bibliographic Details
Published in:Applied catalysis. A, General General, 2014-09, Vol.485, p.40-50
Main Authors: Mistri, Rajib, Maiti, Sayantani, Llorca, Jordi, Dominguez, Montserrat, Mandal, Tapas Kumar, Mohanty, Paritosh, Ray, Bidhan Chandra, Gayen, Arup
Format: Article
Language:English
Subjects:
Catalysts
Copper
Crystallites
Cyclohexane
Hercynite
Iron
Liquid phase oxidation
Spinel
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Summary:Copper ion substituted MAl sub(2)O sub(4) (M = Mg, Mn, Fe, Ni and Zn) spinels, Cu sub(x)M sub(1-x)Al sub(2)O sub(4)(x = 0.03 and 0.05), have been synthesized by a single step solution combustion method. Of the various compositions studied the 3 at.% copper ion substituted hercynite, Cu sub(0.03)Fe sub(0.97)Al sub(2)O sub(4), reported here for the first time, is shown to be much more active (~92% conversion with ~99% selectivity) than other spinel analogues towards liquid phase oxidation of cyclohexane in acetonitrile with H sub(2)O sub(2) as oxidant in air. Powder XRD analyses have revealed formation of pure hercynite phases. The least-square refined lattice parameters obtained from XRD data together with microstructural data by HRTEM have indicated copper ion substitution in the spinel lattice. The oxidation state of copper has been established as +2 from XPS analysis and it seem to be primarily substituted in the Fe-site of hercynite. Incorporation of the copper in the spinel structure of FeAl sub(2)O sub(4) leading to an ionic interaction is explained to be responsible for the higher oxidation activity observed over the combustion synthesized catalyst than the corresponding impregnated catalyst which contains finely dispersed CuO crystallites. Effect of recycling (repeated thrice) has shown almost no degradation of activity of the copper ion substituted hercynite. In contrast, the analogous impregnated catalyst has shown appreciable loss of activity in the consecutive cycles due to the presence of dispersed CuO crystallites which can agglomerate with ease and subsequently leach out.
ISSN:0926-860X
1873-3875
DOI:10.1016/j.apcata.2014.07.027