Novel Catalyst Composites of Ni- and Co-Based Nanoparticles Supported on Inorganic Oxides for Fatty Acid Hydrogenations

Abstract

In the quest to develop nanometrically defined catalytic systems for applications in the catalytic valorization of agri-food wastes, small Ni-based nanoparticles supported on inorganic solid supports have been prepared by decomposition of organometallic precursors in refluxing ethanol under H₂ atmosphere, in the presence of supports exhibiting insulating or semi-conductor properties, such as MgAl₂O₄ and TiO₂, respectively. The efficiency of the as-prepared Ni-based nanocomposites has been evaluated towards the hydrogenation of unsaturated fatty acids under solvent-free conditions, with high selectivity regarding the hydrogenation of C=C bonds. The influence of the support on the catalytic performance of the prepared Ni-based nanocomposites is particularly highlighted.

Keywords: C=C bonds hydrogenation; fatty acids; industrial waste; magnesium aluminum oxide spinel; nickel-based nanoparticles; titanium dioxide anatase; valorization.

Figure 1

(a) Synthesis of both mono-metallic Ni and Co nanocomposites supported on MgAl₂O₄ or TiO₂; (b) synthesis of bi-metallic NiCo nanocomposites supported on MgAl₂O₄ or TiO₂.

Figure 2

TEM micrographs of nickel-based nanocomposite materials: (a) NiNP@MgAl₂O₄ after synthesis and glycerol extracts with particle size distribution (1.4 ± 0.4 nm for 1466 particles); (b) CoNP@MgAl₂O₄ after synthesis and glycerol extracts with particle size distribution (1.2 ± 0.3 nm for 1103 particles); (c) NiCoNP@MgAl₂O₄ after synthesis and glycerol extracts; (d) NiNP@TiO₂ after synthesis and glycerol extracts with particle size distribution (1.6 ± 0.5 nm for 2046 particles); (e) CoNP@TiO₂ after synthesis and glycerol extracts with particle size distribution (1.3 ± 0.3 nm for 1493 particles); (f) and NiCoNP@TiO₂ after synthesis and glycerol extracts with particle size distribution (1.2 ± 0.4 nm for 3868 particles) (see Figures S1–S6 for further TEM micrographs of each material in the Supplementary Materials).

Figure 3

STEM-BF analysis of NiCoNP@TiO₂ showing elemental distribution of Ti (red), Co (green), Ni (cyan), and O (blue).

Figure 4

Magnetization curves with magnification: (a) NiNP@MgAl₂O₄; (b) NiNP@TiO₂; (c) CoNP@TiO₂; (d) NiCoNP@TiO₂; (e) NiCoNP@MgAl₂O₄.

Figure 5

XPS analyses: XPS survey spectra of MgAl₂O₄ support, NiNP@MgAl₂O₄ and NiCoNP@MgAl₂O₄ composites (left column); high-resolution spectrum at the binding energy region of Ni 2p; black, red, and blue continuous traces correspond to Ni(0), NiO, and Co(OH)₂ envelopes used to fit the experimental data (dotted line); the fit was carried out on the Ni 2p_3/2 binding energy (middle column); high-resolution spectrum at the binding region of Co 2p; black, orange, and blue continuous traces correspond to Co(0), CoO, and Co(OH)₂ envelopes used to fit the experimental data (dotted line); the fit was carried out on the Co 2p_3/2 binding energy (right column). For the peak fitting procedures, see the experimental section.