【作者】 吴军良；

【导师】 李忠；

【作者基本信息】 华南理工大学 ， 能源环境材料及技术， 2014， 博士

【摘要】 低温等离子体催化技术可在常温常压下氧化挥发性有机污染物，具有非常广阔的应用前景。该技术目前还存在能耗过高，系统性能易受水蒸气影响等关键问题，研究开发高效的、耐水蒸气影响的催化剂对于提升等离子体催化系统的性能具有重要的研究价值和实际意义。本文主要研究了锰基、镍基、铬基金属有机骨架材料（MIL-101）等催化剂在干湿空气条件下在等离子体催化系统中催化氧化甲苯的性能。本文首先研究了氧化锰催化剂制备条件对其在等离子体催化系统中氧化甲苯活性的影响。研究结果表明，当活性组分Mn负载量为1wt%，焙烧温度为500℃制备的MnOx/γ-Al2O3催化剂具有很高比表面积，1wt%的负载量最接近MnOx在载体γ-Al2O3上的单层负载量。此催化剂应用于等离子体催化反应系统时，其对甲苯的转化率接近100%（能量密度为21J/l），并具有良好的稳定性。本文研究了系列过渡金属氧化物催化剂协同等离子体催化氧化甲苯的性能，实验结果表明，这些催化剂性能的高低顺序如下：NiO/γ-Al2O3> MnO2/γ-Al2O3> CeO2/γ-Al2O3>Fe2O3/γ-Al2O3> CuO/γ-Al2O3。其中的NiO/γ-Al2O3展示出最高的活性，原因是其在等离子体空间分解臭氧，促进活性氧原子生成的性能最强。当Ni负载量为5wt%时，其值接近NiO在载体γ-Al2O3上的单层分散量，使得此氧化镍催化剂在等离子体催化系统中对甲苯转化率最高。本文研究了气体的相对湿度对不同载体(γ-Al2O3、SBA-15、TiO2)制备的镍基催化剂协同等离子体催化氧化甲苯的性能。结果表明，在干气流条件下，镍基催化剂协同等离子体催化氧化甲苯的活性大小顺序为：NiO/γ-Al2O3> NiO/SBA-15> NiO/TiO2，催化剂活性取决于NiO在三种载体上的分散程度，分散程度越高，催化剂的活性越强。在湿气流条件下，水蒸汽浓度对镍基催化剂的活性有明显的负面影响，水蒸汽浓度越高，催化剂活性下降幅度越大，其主要原因是水分子的存在会湮灭等离子体区的高能电子，减少活性物种数量，从而减少甲苯分子和活性物种之间的反应几率；此外，水分子会在催化剂表面上与甲苯、臭氧等物种形成竞争吸附，由于水分子占据了相当部分的反应活性中心位，导致了催化剂活性的下降。三种催化剂受水蒸气负面影响的大小顺序为：NiO/γ-Al2O3> NiO/SBA-15> NiO/TiO2。H2O-TPD表征结果显示，水蒸气在三种催化剂上的脱附活化能顺序是：NiO/γ-Al2O3> NiO/SBA-15> NiO/TiO2，这与三种催化剂受水蒸气负面影响的大小顺序一致。这揭示了催化剂表面与水蒸气的相互作用越强，催化剂活性受水蒸气的负面影响也就越大。本文自行设计了集成DBD等离子体反应器的红外原位池，研究低温等离子体环境下，水蒸气和甲苯在催化剂表面的吸附以及催化剂种类对甲苯降解途径的影响。结果表明：在等离子体催化反应过程中，催化剂表面吸附的水来自于气相中的水蒸气以及甲苯氧化生成的水。甲苯在单独的等离子体场和等离子体催化氧化甲苯反应过程中，都会产生苯甲醛等多种中间产物。有催化剂MnOx/γ-Al2O3或NiO/γ-Al2O3存在，有助于减少等离子体催化反应体系中催化剂表面中间产物产生与累积，其中装载了MnOx/γ-Al2O3，明显减少了反应中间产物的种类，而装载了NiO/γ-Al2O3，明显减少了中间产物的浓度。本文研究了MIL-101在等离子体催化系统中分解甲苯的性能。该材料展现了比CrOx/γ-Al2O3更高的氧化甲苯活性，碳平衡和CO2选择性，其原因是MIL-101具有更强的分解臭氧生成活性氧物种的能力。微波辐射合成法制备的MIL-101对甲苯的氧化性能高于溶剂热合成法制备的MIL-101，其原因可能是前者具有更大的比表面积和孔容，有利于等离子体场内活性物种的扩散和反应。在MIL-101上负载MnOx可进一步提高其催化氧化甲苯和分解臭氧性能。在反应器后部增加Ag/γ-Al2O3催化剂，可完全消除反应尾气中残留的臭氧。更多还原

【Abstract】 Non-thermal plasma technique has unique advantage of rapid oxidation of VOCs at roomtemperature and atmospheric pressure. It is a promising solution to treat VOCs pollution.Nowadays, its two challenges are as follows: one is its low energy efficiency, and the other isthat the performance of the plasma catalysis system would be decreased in the presence ofwater vapor in the gas stream. The key to solve these problems is to develop catalysts withhigh activity and durability to water vapor. In this work, a series of manganese, nickel andchromium-based catalysts were prepared, characterized, and evaluated in plasma under bothdry and moist conditions.The effects of preparation conditions for the MnOx/γ-Al2O3catalysts for toluene oxidationwere investigated in a plasma catalysis system (PCS). Results showed that the catalystMnOx/γ-Al2O3with1wt%Mn loading and calcined at500oC had the higher surface area andthe pore volueme compared to the other MnOx/γ-Al2O3catalysts prepared under differentconditions, and the1wt%Mn loading was close to the monolayer dispersion threshold ofMnOx on γ-Al2O3. The toluene conversion of the PCS reached100%at an input energy of21J/l when the MnOx/γ-Al2O3catalyst with1wt%Mn loading and calcined at500oC wasuesed.The performance of the PCSs with a series of transition metal oxides supported on γ-Al2O3was further investigated. The activities of the catalysts decreased in the following order:NiO/γ-Al2O3> MnO2/γ-Al2O3> CeO2/γ-Al2O3> Fe2O3/γ-Al2O3> CuO/γ-Al2O3. The NiOcatalyst exhibited better performance than the other catalysts, which can be attributed to itsgenerating more toluene-destroying oxygen species by decomposing ozone. When the nickelloading of the NiO/γ-Al2O3catalyst was5wt%, which was close to the monolayer dispersionthreshold of NiO on γ-Al2O3, it improved the performance of the PCSs for toluene conversiondue to its high activity.The effect of water vapor on the performance of a PCS with nickel oxide catalysts loadedon different supports (γ-Al2O3、SBA-15、TiO2) was investigated. The activities of catalysts forthe toluene conversion in dry air decreased in the following order: NiO/γ-Al2O3>NiO/SBA-15> NiO/TiO2, which was dependent on the NiO dispersion on the support. Thehigher NiO dispersion led to the higher activity. The presence of water vapor in the feedstream had a significant negative impact on the performance of the PCS. This reduction inperformance was primarily due to the quenching by water vapor of active species in theplasma and the competitive adsorption of water on the catalyst surfaces. The impact of water vapor on the performance of the catalyst decreased in the following order: NiO/γ-Al2O3>NiO/SBA-15> NiO/TiO2. H2O-TPD results indicated that the desorption activation energiesof water vapor on the catalysts decreased in the following order: NiO/γ-Al2O3>NiO/SBA-15> NiO/TiO2. The catalyst with lower water vapor desorption activation energyhad higher resistance to water vapor.A novel in situ FTIR system was constructed and used to obtain in situ FTIR spectra of thereactive surfaces of the catalysts during the plasma catalysis reaction. It revealed that watermolecules adsorbed on the catalyst surfaces came from both water vapor present in the gasstream and from water vapor formed during the oxidation of toluene. The intermediateproducts such as benzaldehyde were formed during the oxidation of toluene in both cases ofthe plasma system and the PCSs. The presence of catalysts MnOx/γ-Al2O3or NiO/γ-Al2O3reduced the formation of these intermediate products. Interestingly, for the PCSs, the loadingof the catalyst MnOx/γ-Al2O3greatly reduced the species of the intermediate products formed,and the loading of the catalyst NiO/γ-Al2O3greatly decreased the amounts of the intermediateproducts formed during the oxidation of toluene.Catalytic performance of MIL-101in the PCS for toluene removal was finally studied.Results showed that MIL-101catalyst had higher performance for toluene decomposition thanγ-Al2O3and CrOx/γ-Al2O3. It was attributed to the higher dispersion of CrOx on the MIL-101than on the γ-Al2O3support, leading to a better performance of decomposing ozone toproduce atom oxygen species. The MIL-101prepared by microwave heating method showedbetter performance compared to hydrothermal synthesis method. The loading of MnOx onMIL-101further promoted its performance. When Ag/γ-Al2O3was placed behind the plasmacatalyst reactor, outlet ozone was nearly eliminated and then the toluene oxidation was furtherimproved.更多还原