Oxygen activation on ultra-disperse CeOx clusters deposited on MgO hexagonal plates

RAQUEL PROTELLA; MIGUEL BAÑARES; ALEJO AGUIRRE; MARTA BOSCO; SUSANA TRASOBARES; ESTEBAN FORNERO; SEBASTIÁN COLLINS

Congreso; 7th International Congress on Operando Spectroscopy; 2023

A low-loading lanthanide (1.8, 3.5 and 7.2 wt.%) catalysts composed of highly disperse CeO2 nanoparticles (3 nm) and clusters (1-3 nm) and Ce single atoms supported on magnesium oxide hexagonal nanoplates (CeO2/MgO-h) were synthesized. Structural characterization by high resolution transmission electron microscopy indicates that MgO-h exposes -preferably- (111) planes, allowing the anchoring of small and highly defective cerium oxide particles, clusters and single atoms. Detailed HAADF and electron energy loss spectroscopy (EELS) analysis revealed that part of the cerium cluster/atoms remains in a Ce3+ state. Catalysts showed enhanced reducibility and better catalytic performance for CO oxidation reaction as compared to a conventional high surface area CeO2 powder. CeO2/MgO-h catalyst presented a lower apparent activation energy than the bulk CeO2 (57 versus 90 kJ/mol, respectively) for CO oxidation. Operando Raman spectroscopy during CO oxidation shown the presence of the typical symmetrical vibration F2 of CeO2 at 462 cm-1, very weak and broad, but more interesting, a broad and intense band at 598 cm-1 indicative of the presence of oxygen defects (oxygen vacancies. In situ infrared showed that high defective CeOx clusters/atoms activate molecular oxygen as peroxide (O2-2) 860 cm-1 and superoxide (O2-) 1125 cm-1 species, allowing a more efficient path for CO oxidation.