Morphology Effects of CeO₂ Nanomaterials on the Catalytic Combustion of Toluene: A Combined Kinetics and Diffuse Reflectance Infrared Fourier Transform Spectroscopy Study

Abstract

CeO2 with varied morphologies (nanopolyhedra, nanorods, and nanocubes) were synthesized via a hydrothermal method and applied to the catalytic combustion of toluene. The physicochemical properties of all catalysts were characterized by transmission electron microscopy, N2-physisorption, X-ray diffraction, H2-temperature-programmed reduction (H2-TPR), X-ray photoelectron spectroscopy (XPS), and in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The CeO2 nanopolyhedra showed superior catalytic activity compared to CeO2 nanorods and nanocubes. Kinetic studies showed that the catalytic combustion of toluene processed through the Mars–van-Krevelen (MvK) mechanism and the oxidation of the reduced CeO2 surface by molecular oxygen are the rate-determining steps in the low-temperature region. The XPS and H2-TPR results showed that CeO2 with varied morphologies had distinct oxygen distribution, especially surface lattice oxygen. A linear relationship between surface lattice oxygen and catalytic activity was observed, indicating that surface lattice oxygen played an important role in the catalytic activity of toluene combustion. Furthermore, the in situ DRIFTS results provided a full roadmap of catalytic combustion of toluene: toluene first rapidly adsorbed onto the surface of CeO2 to form molecularly adsorbed toluene, which then reacted with the surface hydroxyl groups to generate benzyl species without O2. The benzyl species could be further oxidized to benzyloxy, benzaldehyde, and benzoate species, and finally fully oxidized to CO2 and H2O. All these results indicated that the reactivity of surface lattice oxygen was crucial on the catalytic combustion of toluene, providing a basic understanding for the catalytic combustion of toluene on CeO2 with varied morphologies.

Elucidating Ru Distribution State of Ru‐Promoted Pr2Sn2O7 Pyrochlore and its Effect on the Catalytic Performance for Toluene Deep Oxidation

“…Afterwards, a feed with5 % O 2 balanced in Ar was switched into the in situ cell. Figure S5a displays that a peak at 1260 cm −1 is observed, which belong to the surface oxygen species defined as O δ− (0<δ<1) [24] . With time extension, the intensity of the peak increases and reaches stable after 20 min, indicating that the catalyst surface is saturated by O 2 .…”

“…Figure S5a displays that a peak at 1260 cm À 1 is observed, which belong to the surface oxygen species defined as O δÀ (0 < δ < 1). [24] With time extension, the intensity of the peak increases and reaches stable after 20 min, indicating that the catalyst surface is saturated by O 2 . After 30 minutes, an Ar flow was switched into the cell.…”

Effect of CeO2 morphology on the catalytic properties of Au/CeO2 for base-free glucose oxidation

“…The ν 0 , ν′, u 0 and u′ peaks are assigned to Ce 3+ species, and the other six peaks correspond to Ce 4+ species. 34 The contents of Ce 3+ are calculated by the ratio of the Ce 3+ peak areas and the total peak areas of Ce 4+ and Ce 3+ , and the results are also listed in Table 1. For the CeO 2 supports, R-CeO 2 exhibits the highest Ce 3+ content (14.2%), followed by C-CeO 2 (13.7%) and O-CeO 2 (12.7%).…”

Insight into the pH effect on the oxygen species and Mn chemical valence of Co–Mn catalysts for total toluene oxidation

“…55 It appeared after 20 min and increased gradually, suggesting the formation of phenolate by the reaction of benzoate with lattice oxygen in the absence of oxygen. As time goes on, the peaks at 1725, 1797, 1862 and 1945 cm −1 were observed, which were related to the symmetric and asymmetric CO stretching vibrations of anhydride species, [59][60][61][62] and the increasing band intensity implies that the intermediates can interact with lattice oxygen and produce anhydride even without the surface adsorbed oxygen species. The peak at 1390 cm −1 is ascribed to the carbonates.…”