Operando ME-DRIFTS study of reaction intermediates during toluene oxidation on CeO2 nanoparticles supported on MgO hexagonal plates

Abstract

Operando DRIFT spectroscopy was employed to investigate the intermediates involved in the oxidation of toluene on highly dispersed ceria nanoparticles supported on magnesium oxide hexagonal nanoplates. Small CeO2 nanoparticles dispersed on magnesium oxide hexagonal nanoplates showed enhanced catalytic performance to total toluene combustion 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. The results revealed a stepwise reaction pathway for toluene oxidation on the catalyst surface. Initially, toluene is molecularly adsorbed and reacts with surface oxygen species to produce intermediate benzyl (C6H5CH2-). Next, benzyl is stepwise oxidized to benzyloxy/benzyl alcohol, benzaldehyde, and benzoate. Further 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, formates species are rapidly oxidized to CO2 on the CeO2/MgO catalyst and do not accumulate on the surface, due to the enhanced redox capacity and higher presence of oxygen vacancies of the supported nanoparticles.