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 degrees 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.