Study Of Catalytic Combustion Of VOCs Over Manganese-based Catalysts

Catalytic combustion is an effective technique for the elimination of volatile organic compounds (VOCs) due to its low energy consumption and high efficiency. Also, catalytic combustion has been paid much attention for its simple equipment requirement, safe operation and more importantly without associated pollution such as nitrogen oxides (NOX) production during the process. Highly active catalyst is the key to catalytic combustion. For the elimination of VOCs including chlorinated volatile organic compounds (CVOCs), noble metal catalysts and Cr-based catalysts are usually employed. Noble metal catalysts such as Pd and Au have been proved to be very effective; however, the high costs of the catalysts limit their applications. For the Cr-based catalysts, they should be carefully treated because of their toxicity. but the have practical limitations for the high price. Some chromium-based catalysts have toxic so we had better not to use them freely. Some other non-noble metal catalysts were also reported, but they often have low activities. Therefore, the aim of this thesis is to develop economic catalysts with high efficiency. The mains contents of the thesis are as follows:1. A series of Ce1-xMnxO2 catalysts were prepared using a sol-gel method and tested for catalytic oxidation of CH2Cl2. The results indicated that these catalysts were highly active in the oxidation of CH2Cl2, with a complete oxidation temperature of 480℃. The XRD results suggested that solid solution was formed due to the incorporation of Mn in the CeO2 lattice. The XPS results indicated that the Mn species in the catalysts were in oxidation states of +3 and +4. The H2-TPR showed that the addition of Ce in the catalyst remarkably lowered the reduction temperature of the lattice oxygen in MnOx. The intrinsic reactivity calculated based on the Mn content in the catalyst followed the order of Ce0.8Mn0.2O2> Ce0.6Mn0.4O2> Ce0.5Mn0.5O2> Ce0.4Mn0.6O2> Ce0.2Mn0.8O2> CeO2> MnOx. It could be concluded that the enhancement of the reactivity was due to the easier reduction of the lattice oxygen of MnOx. 2. Manganese oxide octahedral molecular sieves (OMS-2) were synthesized using KMnO4 and MnSO4 as the precursors by a reflux method under acidic conditions. The synthesized OMS-2 was tested for catalytic oxidation of CH2Cl2 and characterized by SEM/XRD techniques. It was found that OMS-2 has high activity on the oxidation of CH2Cl2. The SEM image indicated that the OMS-2 molecular sieve is in form of nanorod, while the XRD result showed that the material was a manganese oxide octahedral molecular sieve with the cryptomelane-type structure.3. Ce/OMS-2 catalysts with different Ce contents were synthesized using OMS-2 as the precursor by an impregnation method. The Ce/OMS-2 catalysts were tested for CH2Cl2 oxidation and their thermal stability was also investigated. It was found that the 1.0Ce/OMS-2 catalyst showed the highest activity for CH2Cl2 oxidation in the Ce/OMS-2 catalysts. the H2-TPR results showed that for the 1.0Ce/OMS-2 catalyst the reduction peaks shifted to lower temperatures compared with others, which implied that the catalyst had better redox property. This may be the main reason to interpret high activity of the 1.0Ce/OMS-2 catalyst. Moreover, the catalyst showed high thermal stability during the reaction.4. Al/OMS-2 catalysts with different Al contents were synthesized using OMS-2 as the precursor by an impregnation method. The Al/OMS-2 catalysts were tested for CH2Cl2 oxidation. The results indicated that the activities of the Al/OMS-2 catalysts first increased and then declined with increasing Al loading. The H2-TPR showed that for the 1.0Al/OMS-2 catalyst the reduction peaks shifted to lower temperatures, indicating that the catalyst had better redox property compared to others; however, there may be more facts that govern the catalytic behaviors of the catalysts, which needs further investigation.