α-Fe2O3-supported Co3O4 nanoparticles to construct highly active interfacial oxygen vacancies for ozone decomposition

Effects on structure by spectroscopic investigations, valence state and morphology properties of FeCo-containing SnO2 catalysts for glycerol valorization to cyclic acetals

The effects on the structure, valence state and morphological properties of FeCo-containing SnO2 nanostructured solids were investigated. The physicochemical features were tuned by distinct synthesis routes e.g., sol-gel, coprecipitation and nanocasting, to apply them as catalysts in the glycerol valorization to cyclic acetals. Based on Mössbauer and XPS spectroscopy results, all nanosized FeCoSn solids have Fe-based phases, which contain Co and Sn included in the structure, and well-dispersed Fe3+ and Fe2+ surface active sites. Raman, FTIR and EPR spectroscopies measurements of the spent solids demonstrated structural stability for the sol-gel based solid, which is indeed responsible for the highest catalytic performance, among the nanocasted and coprecipitated counterparts. Morphological and elemental analyses illustrated distinct morphologies and composition on solid surface, depending on the synthesis route. The Fe/Co and Fe/Sn surface ratios are closely related to the catalytic performance. The improved glycerol conversion and selectivities of the solid obtained by sol-gel method was ascribed to the leaching resistance and the Sn action as a structural promoter.

Synergistic effects of copper and oxygen vacancies in enhancing the efficacy of partially crystalline CuMnxOy catalyst for ozone decomposition

To tackle the challenge of ground-level ozone pollution, this study proposed a potential catalytic design approach for ozone decomposition using Cu-Mn bimetallic oxide. This approach is grounded in an understanding of the intrinsic reactivity for catalyst and incorporates a novel potassium-driven low-temperature oxidation process for catalyst synthesis. The research highlights the creation of a highly reactive Cu-Mn oxide phase with extensive defect coverage, leading to significantly increased reaction rates. It also identifies the MnO2(100) facet as a crucial active phase, where oxygen vacancies simultaneously enhance O3 adsorption and decomposition, albeit with a concurrent risk of O2 poisoning due to the stabilization of adsorbed O2. Crucially, the incorporation of Cu offsets the effects of oxygen vacancies, influencing conversion rates and lessening O2 poisoning. The synergistic interplay between Cu and oxygen vacancies elevates the performance of the defect-rich Cu-Mn oxide catalyst. By combining computational and experimental methods, this study not only advances the understanding of the Cu-Mn oxide system for ozone decomposition but also contributes valuable insights into developing more efficient catalysts to mitigate ozone pollution.

Effect of Interlayer Anions on NiFe Layered Double Hydroxides for Catalytic Ozone Decomposition

NiFe layered double hydroxides (NiFe-LDH) exhibited an outstanding performance and promising application potential for removing ozone. However, the effect of interlayer anions on ozone removal remains ambiguous. Here, a series of NiFe-LDH with different interlayer anions (F-, Cl-, Br-, NO3-, CO32-, and SO42-) were prepared to investigate the effect of the interlayer anion on ozone removal for the first time. It was found that the interlayer anions are a key factor affecting the water resistance of the NiFe-LDH catalyst under moist conditions. NiFe-LDH-CO32- exhibited the best water resistance, which was much better than that of NiFe-LDH containing other interlayer anions. The in situ DIRFTS demonstrates that the carbonates in the interlayer of NiFe-LDH-CO32- will undergo coordination changes through the interaction with water molecules under moist conditions, exposing new metal sites. As a result, the newly exposed metal sites could activate water molecules into hydroxyl groups that act as active sites for catalyzing ozone decomposition. This work provides a new insight into the interlayer anions of LDH, which is important for the design and development of LDH catalysts with excellent ozone removal properties.

Efficient ozone decomposition in high humidity environments using novel iron-doped OMS-2-loaded activated carbon material

This study effectively addresses the rapid deactivation of manganese-based catalysts in humid environments during ozone decomposition by introducing iron-doped manganese oxide octahedral molecular sieve (Fe-OMS-2) catalysts supported on activated carbon (AC). By optimizing the doping ratio of Fe-OMS-2, the Fe-OMS-20.5/AC catalyst achieves nearly 100% ozone decomposition efficiency across a wide range of relative humidity levels (0 to 60%), even at elevated air flow rates of 800 L·g-1·h-1, outperforming standalone AC, Fe-OMS-2, or a simple mixture of OMS-2 and AC. The Fe-OMS-20.5/AC catalyst features a porous surface and a mesoporous structure, providing a substantial specific surface area that facilitates the uniform distribution of the Fe-OMS-2 active phase on the AC surface. The incorporation of Fe3+ ions enhances electron transfer between valence state transitions of Mn, thereby improving the catalyst's efficiency in ozone decomposition. Additionally, the AC component protects catalytic sites and enhances the catalyst's humidity resistance. In conclusion, this research presents a novel strategy for developing highly efficient and cost-effective ozone decomposition catalysts that enhance dehumidification, significantly contributing to industrial ozone treatment technologies and advancing environmental protection.

Defluorination of perfluorooctanoic acid and perfluorooctane sulfonic acid by heterogeneous catalytic system of Fe-Al2O3/O3: Synergistic oxidation effects and defluorination mechanism

In this study, catalytic ozonation by Fe-Al2O3 was used to investigate the defluorination of PFOA and PFOS, assessing the effects of different experimental conditions on the defluorination efficiency of the system. The oxidation mechanism of the Fe-Al2O3/O3 system and the specific degradation and defluorination mechanisms for PFOA and PFOS were determined. Results showed that compared to the single O3 system, the defluorination rates of PFOA and PFOS increased by 2.32- and 5.92-fold using the Fe-Al2O3/O3 system under optimal experimental conditions. Mechanistic analysis indicated that in Fe-Al2O3, the variable valence iron (Fe) and functional groups containing C and O served as important reaction sites during the catalytic process. The co-existence of 1O2, OH, O2- and high-valence Fe(IV) constituted a synergistic oxidation system consisting of free radicals and non-radicals, promoting the degradation and defluorination of PFOA and PFOS. DFT theoretical calculations and the analysis of intermediate degradation products suggested that the degradation pathways of PFOA and PFOS involved Kolbe decarboxylation, desulfonation, alcoholization and intramolecular cyclization reactions. The degradation and defluorination pathways of PFOA and PFOS consisted of the stepwise removal of -CF2-, with PFOS exhibiting a higher defluorination rate than PFOA due to its susceptibility to electrophilic attack. This study provides a theoretical basis for the development of heterogeneous catalytic ozonation systems for PFOA and PFOS treatment.