Abstract
The functionalized Shvo’s catalyst precursor {3,4-[p-(EtO)3Si(CH2)3OPh]2-2,5-Ph2(η4-C4CO)}Ru(CO)3 (1) was covalently immobilized to the surface of magnetic nanoparticles, MNPs, including magnetite (Fe3O4) and magnetite covered by one, two and three independently added silica (SiO2) coatings (Fe3O4@SiO2, Fe3O4@SiO2@SiO2, Fe3O4@SiO2@SiO2@SiO2) resulting in the corresponding ruthenium catalysts Fe3O4@Ru (2a), Fe3O4@SiO2@Ru (2b), Fe3O4@SiO2@SiO2@Ru (2c), and Fe3O4@SiO2@SiO2@SiO2@Ru (2d). These catalysts were characterized by FT-IR, TEM, EDX, powder XRD, BET surface area analysis and BJH pore size and volume analysis. The catalytic performances of 2a–2d were tested for the conversion of levulinic acid (LA) to gamma-valerolactone (GVL) using formic acid (FA) as the hydrogen source. The catalysts were separated from the reaction mixture by using an external magnet. Catalysts on the silica coated MNPs showed higher activity than that of immobilized directly to Fe3O4. There were no significant differences in TONs, TOFs and yields of GVL using catalysts 2b–2d. Leaching test of the four catalysts showed that by increasing the number of independent silica coatings on the surface of magnetite significantly decreased iron leaching. The recyclability of 2b was investigated and it was reused several times without significant loss of the catalytic activity. Hot filtration test of 2c and 2d has established that the catalytic activity was due to the supported ruthenium catalyst and not from some active ruthenium species leached from the solid support to the solution under the reaction conditions.
Highlights
Sustainable chemistry and chemical processes should use resources, including energy, at a rate at which they can be replaced naturally, and the generation of waste cannot be faster than the rate of their remediation [1]
We have recently reported the synthesis of silica supported Shvo's catalysts, which were successfully tested for the conversion of levulinic acid (LA) and formic acid (FA) to GVL in good to high yields [18]
2.5 Hot filtration test of immobilized Shvo's catalysts To a solution of 1 mL LA (1.28 g, 11.02 mmol) and 1 mL FA (1.14 g, 24.77 mmol) in 2 mL of d6-DMSO in a 25 mL three-neck round-bottom flask equipped with a condenser and a mechanical stirrer, a certain amount of magnetic nanoparticles (MNPs)–supported Shvo–type catalyst
Summary
Sustainable chemistry and chemical processes should use resources, including energy, at a rate at which they can be replaced naturally, and the generation of waste cannot be faster than the rate of their remediation [1]. 2.1 Preparation of magnetite and silica-coated magnetite supports 2.1.1 Magnetite (Fe3O4) To a stirred solution of FeCl3 × 6 H2O (5.07 g, 18.76 mmol) and FeCl2 × 4 H2O (1.86 g, 9.38 mmol) in deionized water (150 mL) in a 250 mL three–neck round–bottom flask equipped with a condenser and a mechanical stirrer, NaOH was added (3.00 g, 75.00 mmol) at room temperature under nitrogen.
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