Various MnO2 structures have been extensively applied in catalysis. In this study,γ-MnO2,α-MnO2, and δ-MnO2 with corresponding rod, tube, and hierarchical architecture morphologies were prepared and applied for the...Various MnO2 structures have been extensively applied in catalysis. In this study,γ-MnO2,α-MnO2, and δ-MnO2 with corresponding rod, tube, and hierarchical architecture morphologies were prepared and applied for the catalytic oxidation of chlorobenzene (CB). The redox ability, H2O activation behavior, and acidity of MnO2 were analyzed using a range of techniques, including TPR, H2O-TPD, XPS, and pyridine-IR. The catalytic activities in CB oxidation were assessed;this revealed that γ-MnO2 exhibited the highest activity and best stability, owing to its enriched surface oxygen vacancies that functioned to activate O2 and H2O, and capture labile chlorine, which reacted with dissociated H2O to form HCl. All the MnO2 phases generated toxic polychlorinated by-products, including CHCl3, CCl4, C2HCl3, and C2Cl4, indicating the occurrence of electrophilic chlorination during CB oxidation. In particular, the dichlorobenzene detected in the effluents of α-MnO2 might generate unintended dioxins via a nucleophilic substitution reaction.展开更多
It has been generally unclear over the mechanism of inhibitory influence of silicate on structural rearrangement or solely physical adsorption onto manganese dioxide （MnO2） about the decomposition of hydrogen peroxi...It has been generally unclear over the mechanism of inhibitory influence of silicate on structural rearrangement or solely physical adsorption onto manganese dioxide （MnO2） about the decomposition of hydrogen peroxide （H2O2）. Consequently, several experiments were carried out by using MnO2 as a catalyst for the decomposition of H2O2 in a concentration series under certain concentrations of silicates. The silicates were analyzed by using a molybdenum blue colorimetric method. The results showed that the determination of silicates was inhibited by H2O2, whose inhibitory effect was greatly increased by increasing its concentration, but not limited by pH. SEM-EDX （scanning electron microscopy-energy dispersive x-ray spectrometry） results showed that the adsorption of silicates onto the surface of MnO2 was not purely via a structural rearrangement, with increasing Mn atoms protruding on the outer surface by covering oxygen and silicon atoms. XRD （X-ray diffraction） and FTIR （Fourier transform infrared） spectra results further revealed no significant total crystal structural changes in MnO2 after the adsorption of silicates, but only a small shift of 0.21° at 2e from 56.36° to 56.15° , and a FTIR vibration showed at around 1 050 cm-1. The results, therefore, showed that silicate adsorption onto MnO2 took place via both surface adsorption and structural rearrangement by interfacial reaction.展开更多
Knowledge of the catalytic performances of different crystalline phases of a material is vital for the development of superior catalysts. In this study, different phases of MnO2 （（α,β,γ and δ） have been prepare...Knowledge of the catalytic performances of different crystalline phases of a material is vital for the development of superior catalysts. In this study, different phases of MnO2 （（α,β,γ and δ） have been prepared by the oxidation of Mn^2＋, and their catalytic performances were evaluated using the aerobic oxidation of benzyl alcohol to benzaldehyde as a model reaction, α-MnO2 promoted the reaction to the highest yield. However, when the yields were normalized by the corresponding surface areas, δ-MnO2 exhibited the highest specific activity and a-MnO2 the lowest, indicating that the diverse microstructures resulting from the crystalline phase have a profound effect on catalytic performance, α-MnO2 showed the highest catalytic stability, resulting from its unchanged composition and morphology after use. Informed by the experimental results, a possible reaction mechanism involving the Mars-van Krevelen process was proposed. This work provides useful information for the development of effective catalysts for aerobic oxidation.展开更多
基金supported by the Outstanding Youth Project of Zhejiang Natural Science Foundation(LR19E080004)the National Natural Science Foundation of China(51478418)~~
文摘Various MnO2 structures have been extensively applied in catalysis. In this study,γ-MnO2,α-MnO2, and δ-MnO2 with corresponding rod, tube, and hierarchical architecture morphologies were prepared and applied for the catalytic oxidation of chlorobenzene (CB). The redox ability, H2O activation behavior, and acidity of MnO2 were analyzed using a range of techniques, including TPR, H2O-TPD, XPS, and pyridine-IR. The catalytic activities in CB oxidation were assessed;this revealed that γ-MnO2 exhibited the highest activity and best stability, owing to its enriched surface oxygen vacancies that functioned to activate O2 and H2O, and capture labile chlorine, which reacted with dissociated H2O to form HCl. All the MnO2 phases generated toxic polychlorinated by-products, including CHCl3, CCl4, C2HCl3, and C2Cl4, indicating the occurrence of electrophilic chlorination during CB oxidation. In particular, the dichlorobenzene detected in the effluents of α-MnO2 might generate unintended dioxins via a nucleophilic substitution reaction.
基金Supported by the Provincial Basic Research Program of Hebei Education Department(ZD2015110)the National Special Project on Key Technologies and Demonstration of Wetland Ecological Restoration in the Haihe River Basin(2014ZX07203008)
文摘It has been generally unclear over the mechanism of inhibitory influence of silicate on structural rearrangement or solely physical adsorption onto manganese dioxide （MnO2） about the decomposition of hydrogen peroxide （H2O2）. Consequently, several experiments were carried out by using MnO2 as a catalyst for the decomposition of H2O2 in a concentration series under certain concentrations of silicates. The silicates were analyzed by using a molybdenum blue colorimetric method. The results showed that the determination of silicates was inhibited by H2O2, whose inhibitory effect was greatly increased by increasing its concentration, but not limited by pH. SEM-EDX （scanning electron microscopy-energy dispersive x-ray spectrometry） results showed that the adsorption of silicates onto the surface of MnO2 was not purely via a structural rearrangement, with increasing Mn atoms protruding on the outer surface by covering oxygen and silicon atoms. XRD （X-ray diffraction） and FTIR （Fourier transform infrared） spectra results further revealed no significant total crystal structural changes in MnO2 after the adsorption of silicates, but only a small shift of 0.21° at 2e from 56.36° to 56.15° , and a FTIR vibration showed at around 1 050 cm-1. The results, therefore, showed that silicate adsorption onto MnO2 took place via both surface adsorption and structural rearrangement by interfacial reaction.
基金supported by the National Natural Science Foundation of China (21671152,51672193 and 51420105002)the Funding for 551 talents of Wenzhou
文摘Knowledge of the catalytic performances of different crystalline phases of a material is vital for the development of superior catalysts. In this study, different phases of MnO2 （（α,β,γ and δ） have been prepared by the oxidation of Mn^2＋, and their catalytic performances were evaluated using the aerobic oxidation of benzyl alcohol to benzaldehyde as a model reaction, α-MnO2 promoted the reaction to the highest yield. However, when the yields were normalized by the corresponding surface areas, δ-MnO2 exhibited the highest specific activity and a-MnO2 the lowest, indicating that the diverse microstructures resulting from the crystalline phase have a profound effect on catalytic performance, α-MnO2 showed the highest catalytic stability, resulting from its unchanged composition and morphology after use. Informed by the experimental results, a possible reaction mechanism involving the Mars-van Krevelen process was proposed. This work provides useful information for the development of effective catalysts for aerobic oxidation.
