Monodisperse-porous cerium oxide microspheres as a new support with appreciable catalytic activity for a composite catalyst in benzyl alcohol oxidation

A synergistic catalyst in the form of monodisperse-porous CeO2 microspheres supported Pd nanoparticles (Pd NPs) was synthesized. CeO2 microspheres 4 mu m in size were obtained by a newly developed "sol-gel templating method". The catalyst exhibited superior performance in the oxidation of benzyl alcohol (BzOH) with respect to previously synthesized similar catalysts containing various CeO2 nanostructures as the support and Pd NPs as the active center. The catalyst obtained by the attachment of Pd NPs onto aminated-CeO2 microspheres provided a BzOH conversion of 96.3% and a benzaldehyde formation yield of 91.4% and a good stability in BzOH formation yield in recyclability runs. Large particle size, high surface area and considerable pore volume of monodisperse-porous CeO2 microspheres allowed the synthesis of an agglomeration resistant, composite oxidation catalyst by the attachment of Pd NPs 2.6 nm in size, onto them. Plain CeO2 microspheres selected as the support also exhibited appreciable catalytic activity in BzOH oxidation. The catalytic activity of plain CeO2 microspheres was explained by the formation of oxidative oxygen species due to the presence of multiple oxidation states of cerium [i.e. Ce(iii) and Ce(iv)] on CeO2 microspheres as shown by X-ray photoelectron spectroscopy. Then monodisperse-porous CeO2 microspheres were proposed for the first time, as a new support for an oxidation catalyst due to their high surface area, surface hydroxyl groups allowing facile post-functionalization and reversible Ce(iii)/Ce(iv) switching ability providing an additional catalytic activity and a synergistic interaction. A mechanism was also proposed for the superior catalytic activity of Pd NP decorated-CeO2 microspheres based on the synergistic interaction between CeO2 microspheres with Ce(iii)/Ce(iv) reversible switching ability and Pd NPs.