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. 2019 Aug 9;9(8):1140.
doi: 10.3390/nano9081140.

Fabrication of Bimetal CuFe2O4 Oxide Redox-Active Nanocatalyst for Oxidation of Pinene to Renewable Aroma Oxygenates

Lindokuhle S Mdletshe  1   2 , Peter R Makgwane  3   4 , Suprakas S Ray  5   6
Affiliations

Fabrication of Bimetal CuFe2O4 Oxide Redox-Active Nanocatalyst for Oxidation of Pinene to Renewable Aroma Oxygenates

Lindokuhle S Mdletshe et al. Nanomaterials (Basel). .

Abstract

This study report on the synthesis of spinel CuFe2O4 nanostructures by surfactant-assisted method. The catalysts were characterized by X-ray diffraction (XRD), laser Raman, transition electron microscope (TEM), scanning electron microscope (SEM), energy dispersive X-ray (EDX), hydrogen temperature programmed reduction (H2-TPR), and Brunauer-Teller-Emmett-Teller (BET) surface area techniques. CuFe2O4 was active for pinene oxidation using tertiary butyl hydroperoxide (TBHP) to pinene oxide, verbenol, and verbenone aroma oxygenates. Under optimized reaction conditions, the spinel CuFe2O4 catalyst could afford 80% pinene conversion at a combined verbenol/verbenone selectivity of 76% within the reaction time of 20 h. The changes in catalyst synthesis solvent composition ratios induced significantly varying redox, phases, and textural structure features, which resulted in various catalytic enhancement effect. Characterization results showed the spinel CuFe2O4 catalyst possessing less than 5 wt% impurity phases, Cu(OH)2, and CuO to afford the best catalytic performance. The CuFe2O4 catalyst was recyclable to up to five reaction cycles without loss of its activity. The recyclability of the bimetal CuFe2O4 oxide catalyst was simply rendered by use of an external magnet to separate it from the liquid solution.

Keywords: biomass; copper oxide; iron oxide; nanoparticles; pinene; selective oxidation.

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Conflict of interest statement

The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.

Figures

Scheme 1
Scheme 1
Oxidation reaction of α-pinene to major aroma chemical molecule.
Figure 1
Figure 1
XRD patterns of (a) CuO, (b) Fe2O3, (c) CuFe-1, (d) CuFe-2, (e) CuFe-3, and (f) CuFe-4 catalysts.
Figure 2
Figure 2
Raman vibration modes patterns of CuFe2O4-based catalysts.
Figure 3
Figure 3
Field emission scanning electron microscope (FESEM) microstructure images morphology of CuFe2O4 catalysts.
Figure 4
Figure 4
High-resolution transition electron microscope (HRTEM) different spots images of (a–c) CuFe-4, and (d) its selected area electron diffraction (SAED) rings.
Figure 5
Figure 5
N2 sorption isotherms and pore distribution profiles of CuFe2O4 catalysts. Cu = copper oxide, Fe =iron oxide and EG = ethylene glycol.
Figure 6
Figure 6
H2-TPR profiles of the spinel CuFe2O4-based catalysts.
Scheme 2
Scheme 2
Plausible reaction path for the formation of verbenol and verbenone major products in the oxidation of pinene by tertiary butyl hydroperoxide (TBHP).
Figure 7
Figure 7
Effect of temperature on catalytic performance of CuFe-4 catalyst. Other conditions: Pinene (1 mmol), TBHP (2 mmol), catalyst (100 mg), acetonitrile (10 mL), t = 20 h.
Figure 8
Figure 8
Recyclability performance of CuFe-4 catalyst for pinene oxidation. Other conditions: Pinene (1 mmol), TBHP (2 mmol), catalyst (100 mg), acetonitrile (10 mL), t = 20 h, T = 90 °C.
Figure 9
Figure 9
Comparisons of atmospheric vs. high-pressure conditions for pinene oxidation reaction using CuFe-4 catalyst. Other conditions: Pinene (3 mmol), TBHP (6 mmol), catalyst (300 mg), acetonitrile (30 mL), T = 90 °C, t = 10 h.
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