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.

Advanced Nickel-Based Catalytic Materials on Hydroxyapatite: Effect of the Metal Particle Size on Tri-reforming of Methane

“…Importantly, the Ni 2p XPS core level spectrum of 10Ni@HAP showed three contributions: Ni(0) (51%), NiO (31%), and Ni­(OH) 2 (18%) (Figure b). These results highlight that the organometallic approach is efficient to obtain zero-valent NiNPs, albeit its partial oxidation given its prone oxidation from oxygen traces even under ultra-high vacuum during XPS analysis and manipulation under Ar atmosphere (glovebox), as observed in the characterization of NiNPs catalysts previously reported. , Moreover, the observed Ca/P atomic ratio by ICP AES (1.8) corresponds to the pristine HAP, confirming that the structure of the support remained unaltered during the synthesis (see Table S3 and Figure S14 in the Supporting Information). The organometallic synthetic methodology precludes the formation of Ni 3 (PO 4 ) 2 via the exchange of Ca­(II) by Ni­(II) ions in HAP as reported using incipient impregnation methods, thus avoiding structural changes known to weaken the support structure …”

“…For all of the materials prepared by the organometallic approach, the direct observation of metal nanoparticles was not possible probably due to their small size (see Figure S8 in the Supporting Information). With the purpose of extracting the nanoparticles immobilized on the support and thus determining their mean size, we dispersed the catalytic materials in glycerol taking advantage of the high affinity of metal nanoparticles by this solvent as proven previously by our group . Actually, we could extract more than 80% of nickel from the solid materials as evidenced by ICP-AES for the catalytic materials prepared by the organometallic procedure; for those prepared by the IWI method, the glycerol extraction was not efficient due to the low affinity of the large particles formed for a polar solvent such as glycerol (see Table S2 in the Supporting Information).…”

“…Ni-based materials were prepared through a one-pot organometallic methodology based on our previously reported works. ,,, Thus, in-situ decomposition of bis­(1,5-cyclooctadiene)­nickel(0) was carried out under hydrogen (3 bar), in the presence of hydroxyapatite (HAP) as support and quinidine (QD) as stabilizer (molar ratio Ni:support:stabilizer = 1:4.1:0.9) at 100 °C in ethanol during 18 h ( x Ni-QD@HAP , where x = 5 and 10, meaning the expected weight percentage of nickel on the catalytic material; Scheme ), obtaining a black dispersion. The main parameters were optimized (metal loading, pressure, and reaction time; see the Supplementary Information).…”

“…With the purpose of extracting the nanoparticles immobilized on the support and thus determining their mean size, we dispersed the catalytic materials in glycerol taking advantage of the high affinity of metal nanoparticles by this solvent as proven previously by our group. 19 Actually, we could extract more than 80% of nickel from the solid materials as evidenced by ICP-AES for the catalytic materials prepared by the organometallic procedure; for those prepared by the IWI method, the glycerol extraction was not efficient due to the low affinity of the large particles formed for a polar solvent such as glycerol (see Table S2 in the Supporting Information). Given the negligible vapor pressure of glycerol, TEM analyses were carried out directly from glycerol phases showing the formation of spherical nanoparticles of mean diameters in the range of 2.6−4.4 nm (Table 1 and Figure 1), smaller for those materials containing a lower nickel loading, i.e.…”

“…The design of nickel nanocatalysts exhibiting high surface areas and enhanced reactivity profiles arising from low-coordination sites due to structural defects, and synergistic effects between metal–support interfaces, represents an innovative strategy toward the kinetic stabilization of small nanoparticles that has been widely applied by our group for zero-valent Ni systems immobilized both in a liquid phase (glycerol) and on solid supports (MgAl 2 O 4 , TiO 2 , halloysite).…”