Investigation into the catalytic roles of oxygen vacancies during gaseous styrene degradation process via CeO2 catalysts with four different morphologies

Abstract

CeO2 catalysts with four different morphologies (sphere, rod, octahedral and cube) were successfully synthesized under hydrothermal conditions and showed quite different thermocatalytic activities for gaseous styrene degradation. Unexpectedly, even though its main exposed lattice plane was (111), spherical CeO2 (CeO2-S), presented the highest styrene catalytic degradation activity (T90 =184 ℃) with a styrene degradation rate of 1.36 × 10−3 molstyrene g−1 h−1 at 200 ℃ that was approximately 12 times higher than that of cubic CeO2. A comprehensive structural characterization and mechanistic study found that the four CeO2 samples exhibit different degrees of lattice distortion and different oxygen vacancy concentrations. CeO2-S has the greatest lattice distortion, resulting in abundant oxygen vacancies. Oxygen vacancies were identified to be the main active sites through increasing reactive oxygen generation. Meanwhile, styrene was activated by adsorption of oxygen vacancies. Based on the results of in-situ DRIFTS and XPS measurements, 18O2 isotope tracing experiment and DFT theoretical calculations, the superior thermocatalytic performance of CeO2-S can be attributed to the lesser accumulation of intermediates on its surface, which follows the Langmuir-Hinshelwood (L-H) mechanism (low temperature) and the Mars-van Krevelen (MVK) mechanism (high temperature). In addition, no obvious decrease was observed in the activity of the CeO2-S catalyst for styrene degradation at 210 °C in the presence of water vapor, which is beneficial for the actual industrial application.