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. 2018 Jan 22;8(7):3903-3909.
doi: 10.1039/c7ra13590d. eCollection 2018 Jan 16.

Magnesium surface enrichment of CoFe2O4 magnetic nanoparticles immobilized with gold: reusable catalysts for green oxidation of benzyl alcohol

Wiury C de Abreu  1   2 , Marco A S Garcia  1 , Sabrina Nicolodi  3 , Carla V R de Moura  1 , Edmilson M de Moura  1
Affiliations

Magnesium surface enrichment of CoFe2O4 magnetic nanoparticles immobilized with gold: reusable catalysts for green oxidation of benzyl alcohol

Wiury C de Abreu et al. RSC Adv. .

Abstract

Gold nanoparticles have shown excellent activity for selective oxidation of alcohols; such catalytic systems are highly dependent on the initial activation of the substrates, which must occur on the catalyst surface in heterogeneous catalysts. In many cases, an extra base addition is required, although the basicity of the support may also be of significant importance. Here, we explored the intrinsic basicity of magnesium-based enrichments on CoFe2O4 magnetic nanoparticles for the oxidation of benzyl alcohol using molecular oxygen as oxidant. The MgO and Mg(OH)2 enrichments enabled gold impregnation, which was not possible on the bare CoFe2O4 nanoparticles. The Au/MgO/CoFe2O4 and Au/Mg(OH)2/CoFe2O4 catalysts reached 42% and 18% conversion, respectively without base promotion, in 2.5 hour and 2 bar of O2. When the catalysts were tested with sub-stoichiometric amounts of base, they became more active (>70% of conversion) and stable in successive recycling experiments without metal leaching, under the same reaction conditions. We also showed the oxide phases of the enrichments performed using Rietveld refinements and how the Mg(OH)2 phase interferes with the activity of MgO-based materials.

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Conflict of interest statement

There are no conflicts to declare.

Figures

Fig. 1
Fig. 1. Magnetization as a function of the applied magnetic field for bare CoFe2O4, MgO/CoFe2O4, Mg(OH)2/CoFe2O4 at room temperature. The hysteresis loops were recorded with a magnetic field cycled between −22 kOe and +22 kOe.
Fig. 2
Fig. 2. Rietveld refinement plot for (a) Au/MgO/CoF2O4 and (b) Au/Mg(OH)2/CoF2O4 catalysts, showing the observed, calculated and difference pattern.
Fig. 3
Fig. 3. TEM images of (a) Au/MgO/CoF2O4 and (b) Au/Mg(OH)2/CoF2O4 catalysts and the corresponding size distribution histograms.
Fig. 4
Fig. 4. XPS spectra of samples (a) Au/MgO/CoF2O4 and (b) Au/Mg(OH)2/CoF2O4. Mg 2s is represented by the red line fitting and the Au 4f fitting is represented by the blue line.
Fig. 5
Fig. 5. Influence of the reaction time on the conversion and selectivity in the oxidation of benzyl alcohol over (a) Au/MgO/CoFe2O4 and (b) Au/Mg(OH)2/CoFe2O4 catalysts.
Fig. 6
Fig. 6. Recycling of (a) Au/MgO/CoFe2O4 and (b) Au/Mg(OH)2/CoFe2O4 catalysts in the oxidation of benzyl alcohol.
See this image and copyright information in PMC

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