Ce–UiO-66 Derived CeO₂ Octahedron Catalysts for Efficient Ketonization of Propionic Acid

Abstract

CeO2–UiO octahedron catalysts derived from cerium-based metal–organic frameworks Ce–UiO-66 were synthesized for vapor-phase ketonization of propionic acid. Characterizations showed the CeO2–UiO octahedron is assembled from nanosized CeO2 crystallites with mesopores. XPS and Raman results indicated that more oxygen vacancies are formed in CeO2–UiO-450 catalyst than in CeO2–P prepared by a precipitation method. Intrinsic ketonization rates on CeO2–UiO-450 are improved relative to CeO2–P. At 350 °C, the turnover frequency based on acid–base pair on CeO2–UiO-450 (7.45 s–1) is 1.38 times higher than that on CeO2–P (5.41 s–1). Consistently, the activation energy is lowered from 130.5 kJ/mol for CeO2–P to 109.0 kJ/mol for CeO2–UiO-450. Infrared spectroscopy results showed that monodentate carboxylate is the active adsorption configuration, and its consumption is much faster on CeO2–UiO-450 than on CeO2–P. A linear correlation between the concentration of oxygen vacancy and intrinsic ketonization rate is found, indicating that the oxygen vacancy promotes ketonization on CeO2.