The Preparation Of Mn-Based Catalysts And Their Catalytic Activities For Deep Catalytic Oxidation Of O-xylene

Benzene, toluene and xylene as important chemical raw materials and good organic solvents are widely used in pharmaceutical, chemical and building decoration materials in industrial production. This kind of Volatile Organic Compounds(VOCs) is harm to the environment and human health after discharge into the environmrent. In many VOCs control method, the catalytic technology is the most promosing method at present. In this paper, a series of catalysts with excellent performance at lower temperature have been prepared for o-xylene catalytic. The main results are as follows:(1) Ag-OMS-2-0.05-400 were synthesized by a one-step method using propionaldehyde, silver ammonia and KMn O4 as precursors. Among them, KMn O4 and silver ammonia were as oxidants, propionaldehyde was as reducing agent. Propionaldehydecould react with Ag+ to produce Ag0. At the same time, II-type manganese oxide octahedral molecular sieve(OMS-2) was obtained by the reaction of KMn O4 and propionaldehyde. The results of catalytic combustion showed that catalyst could make o-xylene completely transformed into CO2 and H2 O at 180℃. For comparing, silver doped catalyst 2Ag+-OMS-2 was also prepared by impregnation method. XRD results showed that manganese oxide were all OMS-2(JCDPS-00-020-0908) before and after doped with Ag. The difference is that the absorption peak of Ag2 O appeared in the 2Ag+-OMS-2. While, 2Ag-OMS-2-0.05-400 did not appear any peaks of Ag, which indicated that silver was dispersed in the OMS-2 lattice. BET results showed that the specific surface area of 2Ag-OMS-2-0.05-400 was increased comparing with OMS-2, which maybe due to silver doped into the OMS-2 crystal lattice and increasing the distance between Mn-O-Mn. XPS test results showed that 2Ag-OMS-2-0.05-400 contained rich surface oxygen. 2Ag-OMS-2-0.05-400 existed Ag0 and Ag. there was only Ag+ presenced in 2Ag+-OMS-2. H2-TPR and O2-TPD results showed that 2Ag-OMS-2-0.05-400 had better redox ability.(2) For further research in preparation methods of the one-step method, the amount of silver, silver dispersion and calcination temperature were changed. The results showed that the catalyst with Ag/Mn molar ratio of 2:100, silver of degree 0.05% and calcination temperature 400℃could complete catalytic oxidation of o-xylene at 180℃ due to silver highly dispersed into the lattice of manganese oxide, which can effectively activate lattice oxygen and obviously improve the catalytic properties of the catalysts.(3) In our previous study, we finded that the catalyst of a-Mn O2, which was prepared by KMn O4 as oxidant, Mn(Ac)2 as the reducing agent with p H=8 showed high catalytic activity due to no hydroxide group or H2 O in the catalyst. However, the specific surface area of the material was samller. Morever, they have good catalyst acitivity. However, the specific surface area of the K-Mn catalyst in this system for preparing relatively small, so in order to increase its surface area, the reaction system were added to the surfactant sodium dodecyl benzene sulfonate(SDBS), sodium dodecyl sulfate(SDS), sodium oleate(SO), cetyl trimethyl ammonium bromide(CTAB)). The type of the surfactant, the order of addition of the surfactant and the amount of addition of surfactants were studied. XRD results showed that manganese oxide were all α-Mn O2 before and after added surfactant. BET results showed that the specific surface area of catalyst was increased after added surfactant. SEM results showed that the addition of surfactants, morphology of α-Mn O2 by nano particles to nano wire fluffy. When the addition of SDBS was 0.15 mmol, the catalyst had the maximum specific surface area. The catalyst keep the original system of no hydroxide group or H2 O structural characteristics. It could make o-xylene completely transformed into CO2 and H2 O at 190℃.This dissertation was supported by the National Natural Science Founadation of China(No.21147004), the National Natural Science Founadation of Hebei(No. B2013205100), the Science Foundation of Hebei Normal University(No. L2010Z06) and the Academic Technology Innovation Project of Hebei Normal University(CG2013329355 and CG20141212203448).