Co-precipitation synthesis of mesoporous maghemite for catalysis application

Abstract

Mesoporous magnetic nanoparticles (MNPs) were synthesized using the chemical co-precipitation method. The structure, morphology and magnetic properties of the MNPs were examined by X-ray diffraction (XRD), Mossbauer spectroscopy (MS), Brunauer–Emmett–Teller (BET) method, Transmission Electron Microscopy (TEM) and Vibrating Sample Magnetometer (VSM). The results of XRD and MS indicated that the MNPs were composed of γ-Fe2O3. TEM microphotography showed that the magnetic material was an aggregate of small spherical particles with a size of 6–12 nm. According to the BET data, the agglomeration of individual maghemite nanoparticles lead to formation of a complex mesoporous structure with the specific surface area of 88.3 m2 g−1. The average pore diameter was 5–7 nm, which correlates with the γ-Fe2O3 particles size. The VSM measurement (MS = 40.54 emu g−1, Mr = 5.27 emu g−1, HC = 88 Oe) indicated that the γ-Fe2O3 exhibited weak ferromagnetic and soft magnetic properties confirming the agglomeration of the small γ-Fe2O3 nanoparticles. The synthesized mesoporous maghemite showed excellent ability to absorb polymer protected colloidal palladium particles (Pd-PAM). The magnetic properties of MNPs were not significantly changed after modification with Pd-PAM. The resulting catalyst of Pd-PAM/MNPs showed activity (WC≡C = 3.3 × 10–6 mol s−1) and selectivity (93%) in the hydrogenation of phenylacetylene under mild conditions of 40 °C and 0.1 MPa. The Pd-PAM/MNPs catalyst can be easily recovered with an external magnet and reused for at least seven runs without significant degradation in the catalytic activity and selectivity.