Iron–cobalt spinel oxide nanoparticles with different Fe/Co ratios have been prepared by the combination of chemical precipitation with simultaneous ultrasonic treatment and subsequent mechanical milling. For comparison, their analogues obtained by thermal synthesis were also studied. Phase composition and structural properties of iron–cobalt oxides are investigated by X-ray diffraction and Moessbauer spectroscopy. Their catalytic behavior in methanol decomposition to CO and methane is tested. A well-defined effect of the preparation method and Fe/Co ratio on the reduction and catalytic properties of iron–cobalt samples is established.

Mechanochemically synthesized nano-dimensional iron–cobalt spinel oxides as catalysts for methanol decomposition

Size and crystallinity-dependent magnetic properties of copper ferrite nano-particles

The alkylation of phenol with methanol is conducted over Ni 1− x Co x Fe 2 O 4 ( x =0, 0.2, 0.5, 0.8 and 1.0) type systems prepared via low temperature route. Alkylation leads to predominantly ortho methylation of phenol, yielding o -cresol and 2,6-xylenol as the products. Under optimized conditions, the total ortho selectivity was ≥94%, regardless of the catalyst composition. Only traces of anisole is formed and hardly any other xylenol or cresol isomers are detected. Phenol conversion and the individual selectivities for o -cresol and 2,6-xylenol depend strongly on the catalyst composition. Selectivity for o -cresol was maximum for NiFe 2 O 4 (i.e., when x =0), whereas upon progressive substitution of Co 2+ ions for Ni 2+ ions, the 2,6-xylenol selectivity increases with a concomitant decrease in the o -cresol selectivity. Maximum phenol conversion and 2,6-xylenol selectivity (also total ortho selectivity) were observed over CoFe 2 O 4 ( x =1). The activity and selectivity were shown to be strongly dependent on the surface acid–base properties of the system. The influences of surface acidity, cation distribution in the spinel lattice and various reaction parameters are discussed.

Ferrospinels based on Co and Ni prepared via a low temperature route as efficient catalysts for the selective synthesis of o-cresol and 2,6-xylenol from phenol and methanol

Decomposition of 1-octanol on the spinel system Ga1−x FexCuMnO4

Preparation of simple and mixed ferrospinels of nickel, cobalt and copper and their sulphated analogues by the room temperature coprecipitation method yielded fine particles with high surface areas. Study of the vapour phase decomposition of cyclohexanol at 300 ◦ C over all the ferrospinel systems showed very good conversions yielding cyclohexene by dehydration and/or cyclohexanone by dehydrogenation, as the major products. Sulphation very much enhanced the dehydration activity over all the samples. A good correlation was obtained between the dehydration activities of the simple ferrites and their weak plus medium strength acidities (usually of the Brnsted type) determined independently by the n-butylamine adsorption and ammonia-TPD methods. Mixed ferrites containing copper showed a general decrease in acidities and a drastic decrease in dehydration activities. There was no general correlation between the basicity parameters obtained by electron donor studies and the ratio of dehydrogenation to dehydration activities. There was a leap in the dehydrogenation activities in the case of all the ferrospinel samples containing copper. Along with the basic properties, the redox properties of copper ion have been invoked to account for this added activity. © 2002 Elsevier Science B.V. All rights reserved.

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Study of cyclohexanol decomposition reaction over the ferrospinels, A1−xCuxFe2O4 (A=Ni or Co and x=0, 0.3, 0.5, 0.7 and 1), prepared by ‘soft’ chemical methods

C.S. Narasimhan

Papers

Studies on the decomposition of isopropyl alcohol on Mg Al2-xFexO4