Co-precipitation synthesis of mesoporous maghemite for catalysis application

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 gamma-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 m(2) g(-1). The average pore diameter was 5-7 nm, which correlates with the gamma-Fe2O3 particles size. The VSM measurement (M-S = 40.54 emu g(-1), M-r = 5.27 emu g(-1), H-C = 88 Oe) indicated that the gamma-Fe2O3 exhibited weak ferromagnetic and soft magnetic properties confirming the agglomeration of the small gamma-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 (W-C equivalent to C = 3.3 x 10(-6) mol s(-1)) and selectivity (93%) in the hydrogenation of phenylacetylene under mild conditions of 40 degrees 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.