Magnetic Fe3O4@SiO2-Pt and Fe3O4@SiO2-Pt@SiO2 Structures for HDN of Indole.

The effect of a second porous SiO2 shell in the activity and selectivity of the Fe3O4@SiO2-Pt catalyst in the hydrodenitrogenation of indole is reported. The double Fe3O4@SiO2-Pt@SiO2 structure was prepared by coating Fe3O4 nanoparticles with tetraethyl orthosilicate (TEOS) with a further impregnation of 1.0 wt.% of Pt on the (3-aminopropyl)triethoxysilane functionalized Fe3O4@SiO2 structures. The second porous SiO2 shell, obtained by using a hexadecyltrimethylammonium bromide (CTAB) template, covered the Fe3O4@SiO2-Pt catalyst with a well-defined and narrow pore-sized distribution. The full characterization by TEM, inductively coupled plasma-optical emission spectroscopy (ICP-OES), XRD, and N2 adsorption isotherm at 77 K and vibrating sample magnetometry (VSM) of the catalysts indicates homogeneous core@shell structures with a controlled nano-size of metallic Pt. A significant effect of the double SiO2 shell in the catalytic performance was demonstrated by both a higher activity to eliminate the nitrogen atom of the indole molecule present in model liquid fuel and the improvement of the catalytic stability reaching four consecutive reaction cycles with only a slight conversion level decrease.

Magnetic Fe2O3⁻SiO2⁻MeO2⁻Pt (Me = Ti, Sn, Ce) as Catalysts for the Selective Hydrogenation of Cinnamaldehyde. Effect of the Nature of the Metal Oxide.

The type of metal oxide affects the activity and selectivity of Fe2O3⁻SiO2⁻MeO2⁻Pt (Me = Ti, Sn, Ce) catalysts on the hydrogenation of cinnamaldehyde. The double shell structure design is thought to protect the magnetic Fe2O3 cores, and also act as a platform for depositing a second shell of TiO2, SnO2 or CeO2 metal oxide. To obtain a homogeneous metallic dispersion, the incorporation of 5 wt % of Pt was carried out over Fe2O3⁻SiO2⁻MeO2 (Me = Ti, Sn, Ce) structures modified with (3-aminopropyl)triethoxysilane by successive impregnation-reduction cycles. The full characterization by HR-TEM, STEM-EDX, XRD, N2 adsorption isotherm at -196 °C, TPR-H2 and VSM of the catalysts indicates that homogeneous core-shell structures with controlled nano-sized magnetic cores, multi-shells and metallic Pt were obtained. The nature of the metal oxide affects the Pt nanoparticle sizes where the mean Pt diameter is in the order: ⁻TiO2⁻Pt > ⁻SnO2⁻Pt > ⁻CeO2⁻Pt. Among the catalysts studied, ⁻CeO2⁻Pt had the best catalytic performance, reaching the maximum of conversion at 240 min. of reaction without producing hydrocinnamaldehyde (HCAL). It also showed a plot volcano type for the production of cinnamic alcohol (COL), with 3-phenyl-1-propanol (HCOL) as a main product. The ⁻SnO2⁻Pt catalyst showed a poor catalytic performance attributable to the Pt clusters' occlusion in the irregular surface of the ⁻SnO2. Finally, the ⁻TiO2⁻Pt catalyst showed a continuous production of COL with a 100% conversion and 65% selectivity at 600 min of reaction.