Excellent product selectivity towards 2-phenyl-acetaldehyde and styrene oxide using manganese oxide and cobalt oxide NPs for the selective oxidation of styrene

MnO_x and Co₃O₄ nanoparticles (NPs) were synthesized using the temperature controlled co-precipitation method and were immobilized on the mesoporous metal oxide supports that were synthesized using the inverse surfactant micelle method. The synthesized catalysts were characterized using TEM, SEM, pXRD, N₂-sorption, XPS, and H₂-TPR. From TEM the well-dispersed metal oxide NPs were observed and the interaction of the NPs with the support was confirmed with H₂-TPR. These metal oxide NPs and immobilized metal oxide NPs were employed in the selective oxidation of styrene using tert-butyl hydrogen peroxide (TBHP) as an oxidant. Higher selectivity towards styrene oxide was obtained using Co₃O₄ NPs. MnO_x NPs gave higher selectivity towards 2-phenyl-acetaldehyde while the immobilized metal oxide NPs gave a mixture of products. The catalytic activities of the compared catalysts followed the following decreasing order of MnO_x NPs (646.9 h⁻¹) > Co₃O₄ NPs (338.1 h⁻¹) > Co-MnO₂_350 (54.1 h⁻¹) > Mn-Co₃O₄_350 (44.1 h⁻¹) ˃ MnO₂_350 (35.8 h⁻¹) > Co₃O₄_350 (21.3 h⁻¹) after 8 h of reaction. The catalytic activities and selectivity profiles under various reaction conditions such as solvent type, catalyst amount, styrene to TBHP ratio and temperature are discussed. The catalytic recyclability of immobilized metal oxide NPs on mesoporous metal oxides showed that they are stable, and the structure of the catalyst was retained.