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抗湿性高活性的过渡金属催化剂的制备及其催化燃烧甲苯的性能
Preparation of Transition Metal Oxide Catalysts with High Moisture Resistance and Activity and Their Performance for Catalytic Combustion of Toluene
【作者】 李欣；
【导师】 李忠；
【作者基本信息】 华南理工大学 ， 化学工程， 2012， 博士
【摘要】 催化燃烧法是一种有效治理挥发性有机化合物VOCs (Volatile organic compounds)污染的技术之一。目前面临急迫解决的一个突出问题是,在实际工况中由于水蒸气的存在会导致催化剂活性的急剧下降而影响VOCs的降解效率,因此,研究和开发高活性同时又具备高憎水性的非贵金属催化剂,这对于治理我国南方潮湿环境下的VOCs污染具有非常重要的意义。本文围绕着在高湿度环境下催化燃烧VOCs面临的催化剂抗湿性能差的难题,从理论层面上研究了催化剂的表面性质与其催化氧化VOCs活性和抗水蒸气负面影响的关系；从技术层面上,研制出新型高活性高憎水性的过渡金属基负载型催化材料。本文研究了单组分负载型堇青石催化剂(CoOx/Cordierite, MnOx/Cordierite, CrOx/Cordierite)催化燃烧甲苯的活性。研究结果表明：催化剂CoOx/Cordierite催化燃烧甲苯的活性最高；用乙二醇法制备的催化剂CoOx/Cordierite-EG的催化活性要高于采用浸渍法制备的CoOx/Cordierite的活性,发现这是因为Co物种在催化剂CoOx/Cordierite-EG表面主要是以Co2+的化学价态存在,并且具有更好的分散性。这是本文的创新之处。本文研究了水蒸气对催化剂CoOx/Cordierite, MnOx/Cordierite和CrOx/Cordierite的活性的影响。水蒸汽的存在会导致这三种催化剂的活性下降,这是由于水分子在表面上形成竞争吸附,它们受水蒸汽负面影响大小的顺序为：CoOx/Cordierite> MnOx/Cordierite> CrOx/Cordierite。H2O-TPD分析表明：水蒸气与催化剂CrOx/Cordierite表面的结合能力要弱于其他二种催化剂,因此它的抗水蒸汽影响的能力最强。本文研究了二元复合型催化剂,分别将不同的元素(Mn、Ce、Fe、Cr)掺杂到催化剂CoOx/Cordierite中。研究结果表明：Mn和Ce元素掺杂到CoOx/Cordierite中,能够有效提高催化剂的抗水蒸气的能力；然而Fe和Cr元素的掺杂却会导致催化剂的抗水性能下降。H2O-TPD分析结果表明催化剂CoCe(0.4)Ox/cordierite与水分子的吸附力最弱,使得该催化剂的催化活性受到水蒸气的负面影响最小,其抗湿性能也最好。Ce元素掺杂后的催化剂CoCe(0.4)Ox/cordierite,其表面的Co2+的百分含量得到了增加,而Co3+的百分含量却明显减少,从而削弱了其表面对水分子的吸附能力、增强了其抗湿性能。当相对湿度从55%增至90%时其对甲苯转化率基本维持稳定,其憎水性能明显优于目前文献报道的催化剂。这是本文的创新之处。本文研制了铜锰负载型催化剂并考察了其催化燃烧甲苯的性能。结果表明：复合型铜锰催化剂催化燃烧甲苯的活性要高于各自单组分催化剂的活性。当Cu/Mn匕为1：1时,催化剂CuMn(1)Ox/γ-Al2O3催化氧化甲苯的活性最高,其T90为229℃;XRD、TPR和XPS等分析结果表明：在此催化剂表面存在着Cu1.5Mn1.5O4晶相,从而使得其能够在较低的温度下催化燃烧甲苯。这也是本文的新意之处。本文采用级数动力学模型、MVK动力学模型模拟了催化剂CuMn(1)Ox/γ-Al2O3催化燃烧甲苯的动力学过程。研究结果表明：基于氧化-还原机理的MVK动力学模型适合用来描述甲苯在催化剂CuMn(l)Ox/γ-Al2O3上的催化燃烧反应过程。本文研究了不同载体(γ-Al2O3, TiO2, Cordierite)负载的铜锰催化剂催化燃烧甲苯的活性和抗湿性能。三种催化剂的活性受水蒸汽负面影响大小的顺序为：CuMn(1)Ox/γ-Al2O3> CuMn(1)Ox/TiO2> CuMn(1)Ox/Cordierite。H2O-TPD分析表明：水蒸气与催化剂表面的结合能力的大小顺序为CuMn(1)Ox/γ-Al2O3> CuMn(1)Ox/TiO2> CuMn(1)OX/Cordierite。综合分析表明：催化剂CuMn(1)Ox/Cordierite与水分子结合能力最弱,因此它的催化活性受到水蒸气的负面影响最小,其抗湿性能最强。这是本文的新意之处。本文研制了MnCe(y)Ox/TiO2催化剂并考察了其催化燃烧甲苯的性能。研究结果表明：催化剂MnCe(y)Ox/TiO2对甲苯均有优良的催化活性,其中催化剂MnCe(0.1)Ox/TiO2催化燃烧甲苯的活性最好,这是因为掺杂适量Ce元素能够提高催化剂活性组分的分散和晶格氧的迁移能力,从而提高了催化剂活性。同时,催化剂MnCe(0.1)Ox/TiO2抗水蒸气负面影响能力也得到明显提高。这是本文的创新之处。本文研究了采用超声-氢气还原联合制备CuMnCe(y)Ox/TiO2三元复合催化剂。研究表明：当Cu:Mn:Ce的摩尔比为1：1：0.25时,催化剂CuMnCe(0.25)Ox/TiO2催化燃烧甲苯的活性最高,在甲苯浓度为5.956g/m3以及空速为23000h-1的条件下,甲苯的转化率达到90%时的温度为201℃,其活性已超过目前文献报道的各种非贵金属负载型催化剂的催化活性,已达到或接近国际上报道的贵金属催化剂的活性水平,是本文的创新之处。
【Abstract】 Catalytic combustion is one of the effective techniques for the destruction of VOCs. One of the prominent problems is that the presence of water vapor had a negative effect on catalytic activity, and thus decreased the degradation efficiency of VOCs. Therefore, the studies of non-noble metal catalysts with high activity and moisture resistance is great important for the destruction of VOCs under conditions of high humidity.In order to solve the problem about catalyst deactivation in high humidity circumstance, the effect of surface chemical properties of the catalysts on their activity and moisture resistance was studied. The novel transition metal oxide catalysts with high moisture resistance and activity were prepared from the technical level.The activity of the catalysts CoOx/Cordierite, MnOx/Cordierite and CrOx/Cordierite for toluene oxidation was investigated. The results showed that the activity of the catalyst CoOx/Cordierite was the highest among the three catalysts. The catalyst CoOx/Cordierite-EG prepared by chemical reduction with ethylene glycol had the better activity than the catalyst CoOx/Cordierite prepared by impregnation method. It was mainly attributed to the cobalt (II) species with better dispersion presented on the CoOx/Cordierite-EG catalyst. This is one of the innovations in this work.The influence of water vapor on the catalytic activity of the catalysts CoOx/Cordierite, MnOx/Cordierite and CrOx/Cordierite for toluene oxidation was investigated. The presence of water vapor had a negative effect on the catalytic activity. It was mainly attributed to the competition of water molecules with toluene molecules for adsorption on the active sites. The degree of degradation in the catalytic activity of the catalysts due to presence of water vapor followed the order:CoOx/Cordierite> MnOx/Cordierite> CrOx/Cordierite. H2O-TPD studies showed that the strength of interactions between water molecules with the surface of the catalyst CrOx/Cordierite was weaker than the other two catalysts. As a consequence of that, CrOx/Cordierite exhibited the best durability to water vapor among the three catalysts.In order to further improve the catalytic performance, various transition metals (Mn、Ce、 Fe%Cr) were separately added to the catalyst CoOx/Cordierite. The results showed that the dopping of Ce or Mn on the catalyst CoOx/cordierite can improve its durability towards water vapor poisoning. H2O-TPD showed that the interaction between water molecules with the surface of CoCe(0.4)Ox/cordierite was the weakest. As a result, this catalyst had the best moisture resistance. The dopping of Ce on the catalyst CoOx/cordierite can result in an increase in its Co2+content and a decrease in its Co3+content, which weakened adsorption of the catalyst surface towards water vapor, and thus increased the durability to water vapor. The conversion of toluene on the catalyst CoCe(0.4)Ox/cordierite maintained stabilization when relative humidity varied from55%to90%. The durability of the catalyst CoCe(0.4)Ox/cordierite towards water vapor was much better than that of the catalysts reported in the literatures. This is one of the innovations in this work.The bimetallic catalysts CuMn(y)Ox/y-Al2O3were prepared, and their catalytic activity for the toluene oxidation was examined. The results showed that the activity of the bimetallic catalysts was higher than that of the monometallic catalysts CuOx/γ-Al2O3and MnOx/γ-Al2O3. The activity of CuMn(1)Ox/γ-Al2O3was the best among these catalysts, and its T90, the temperature required for90%toluene conversion, was229℃. It was mainly attributed to the formation of the phase Cu1.5Mn1.5O4in the bimetallic catalyst CuMn(1)Ox/γ-Al2O3. This is one of new points in this work.The catalytic combustion kinetics of toluene over the catalyst CuMn(1)Ox/γ-Al2O3was investigated. The results showed that MVK model based on redox mechanism was suitable to describe the catalytic combustion kinetics of toluene over CuMn(1)Ox/γ-Al2O3.Copper and manganese based catalysts with different supports were prepared. The effect of water vapor on the activity of the catalysts for toluene oxidation was investigated. The degradation of the catalytic activity of the catalysts by water vapor followed the order: CuMn(1)Ox/γ-Al2O3> CuMn(1)Ox/TiO2> CuMn(1)Ox/Cordierite. H2O-TPD studies showed that the strength of interactions between water molecules with the surfaces of the three catalysts followed the order:CuMn(1)Ox/γ-Al2O3> CuMn(1)Ox/TiO2> CuMn(1)Ox/Cordierite. As a consequence of that, CuMn(1)Ox/Cordierite exhibited the best durability to water vapor. This is one of new points in this work.The catalysts MnCe(y)Ox/TiO2were prepared and their catalytic activity for toluene oxidation was investigated. The results showed that the catalyst MnCe(0.1)Ox/TiO2had higher activity and better durability towards water vapor than other catalysts MnCe(y)Ox/TiO2tested. It is ascribed to the higher dispersion of manganese species on the support. This is one of the innovations in this work.The ternary metal oxide catalysts CuMnCe(y)Ox/TiO2were prepared, and their catalytic activity for toluene oxidation was investigated. The results showed that when Cu:Mn:Ce molar ratio=1:1:0.25, the prepared catalyst CuMnCe(0.25)Ox/TiO2exhibited the best activity among the catalysts tested. Under the condition (Toluene concentration=5.956g/m3, GHSV=23000h-1), its T90, the reaction temperature required for90%toluene conversion, was only 201℃. The activity of the CuMnCe(0.25)Ox/TiO2was better than that of the non-noble metal catalysts, and reached or come close to that of the noble metal catalysts reported in the literatures. This is one of the innovations in this work.