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

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.