Physico-chemical properties and catalytic activity of the sol-gel prepared Ce-ion doped LaMnO3 perovskites

Abstract

Ce-doped LaMnO₃ perovskite ceramics (La_1-xCe_xMnO₃) were synthesized by sol-gel based co-precipitation method and tested for the oxidation of benzyl alcohol using molecular oxygen. Benzyl alcohol conversion of ca. 25-42% was achieved with benzaldehyde as the main product. X-ray diffraction (XRD), thermogravimetric analysis (TGA), BET surface area, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction (H₂-TPR), temperature-programmed oxidation (O₂-TPO), FT-IR and UV-vis spectroscopic techniques were used to examine the physiochemical properties. XRD analysis demonstrates the single phase crystalline high purity of the perovskite. The Ce-doped LaMnO₃ perovskite demonstrated reducibility at low-temperature and higher mobility of surface O₂-ion than their respective un-doped perovskite. The substitution of Ce³⁺ ion into the perovskite matrix improve the surface redox properties, which strongly influenced the catalytic activity of the material. The LaMnO₃ perovskite exhibited considerable activity to benzyl alcohol oxidation but suffered a slow deactivation with time-on-stream. Nevertheless, the insertion of the A site metal cation with a trivalent Ce³⁺ metal cation led to an enhanced in catalytic performance because of atomic-scale interactions between the A and B active site. La_0.95Ce_0.05MnO₃ catalyst demonstrated the excellent catalytic activity with a selectivity of 99% at 120 °C.