Operando DRIFT study of highly disperse CeO2 nanoparticles supported on MgO hexagonal plates during toluene oxidation

A. AGUIRRE; ESTEBAN FORNERO; BOSCO MARTA; COLLINS SEBASTIÁN

Congreso; Operando VII - the 7th International Congress on Operando Spectroscopy; 2023

Operando DRIFT spectroscopy is used to identify the key reaction intermediates during toluene oxidation on highly disperse ceria nanoparticles deposited on MgO catalyst. Small CeO2 nanoparticles supported on magnesium oxide hexagonal nanoplates showed enhanced catalytic performance to total toluene combustion as compared to a high surface area polycrystalline CeO2. Selective identification of active surface species was carried out by combining concentration-modulation excitation spectroscopy (c-MES) experiments with phase-sensitive detection (PSD) spectral analysis and a chemometric multivariate curve resolution alternating least squares (MCR-ALS) method. Toluene is molecularly adsorbed and reacts with surface oxygen to produce intermediate benzyl (C6H5CH2-) species. Next, benzyl is stepwise oxidized to benzyloxy/benzyl alcohol, benzaldehyde, and benzoate. The CeO2/MgO-h catalyst produces a higher amount of benzoate species than pure CeO2 during the toluene adsorption, while MgO-h oxidizes the toluene up to benzaldehyde. Later oxidation of benzoate and the aromatic ring produces formate and carbonate species. On pure CeO2, formates accumulate on the ceria surface and only a minor part of them reacts to produce CO2 (and CO). Instead, the formates are fast oxidized to CO2 on the CeO2/MgO-h catalyst and do not accumulate on the surface, due to the enhanced redox capacity and higher presence of oxygen vacancies (and peroxide/superoxide species) of the supported nanoparticles.