Abstract
Catalytic oxidation is one of the most efficient approaches for industrial volatile organic compounds (VOCs) elimination. MnOx-based catalysts have attracted much attention due to their remarkable low-temperature catalytic activity. Here, octahedral layered birnessite-type manganese oxide (OL-1) with layer spacing of 7 Å and cryptomelane type manganese oxide (OMS-2) with tunneled pore diameter of 4.6 × 4.6 Å were synthesized by a reflux method. Following this, Ce-doped OL-1 and OMS-2 were further prepared by an impregnation method with target to improve catalytic performance in toluene oxidation. Results reveal that the OMS-2 material exhibits the best catalytic activity with 90% of toluene decomposed at 224 °C owing to the presence of a large quantity of active lattice oxygen species. Interestingly, the introduction of Ce leads to the formation of large amounts of acidic sites, which limit the oxidation process and enhance the yield of benzoic acid by-product. The findings in the present work are meaningful for deepening our understanding of the role of ceria on metal oxide catalysts and helping us to design effective catalysts for VOC destruction.
Highlights
Volatile organic compounds (VOCs) are one of the major contributors to the formation of secondary pollutants and photochemical smog, leading to a large decline in air quality and concerns regarding human health (Menon et al, 2011; Wu et al, 2016; He et al, 2019)
The H2 consumption results in Figure 7A reveal that the area of H2 reduction peak is attributing to the amounts of active oxygen species, and the reduction area order is consistent with that of the catalytic performance. This indicates the vital role of the active oxygen species in the catalytic oxidation of toluene over these catalysts. It can be speculated Ce ions occupy a certain amount of active sites and block the toluene oxidation process over manganese oxides
Benzoic acid is the only intermediate that can be detected in toluene oxidation, and the intensity of the bands representing carboxylate group increases with the raising of temperature
Summary
Volatile organic compounds (VOCs) are one of the major contributors to the formation of secondary pollutants (e.g., tropospheric ozone, PAN, and secondary organic aerosols) and photochemical smog, leading to a large decline in air quality and concerns regarding human health (Menon et al, 2011; Wu et al, 2016; He et al, 2019). Sun et al (2011) proposed that the refluxing method is better than solid-reaction method for the preparation of OMS-2 material with superior catalytic performance in toluene oxidation. The specific surface areas of prepared materials decrease as follows: CeOMS (72.1 m2/g) > CeOL (71.1 m2/g) > OMS (67.0 m2/g) > OL (23.4 m2/g).
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