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 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.