【作者】 宋磊；

【导师】 陈天虎；

【作者基本信息】 合肥工业大学 ， 矿物学、岩石学、矿床学， 2013， 博士

【摘要】 VOCs(Volatile Organic Compounds)是很多工业过程中排放的主要气体污染物之一,催化氧化可将VOCs在较低的温度下转化为无害的CO2和H2O,是最有前景的处理方法之一。但高活性和长寿命催化剂的缺乏、典型污染物催化氧化过程机理的不明确等问题制约了催化氧化技术的工业应用。针对以上问题本研究以甲苯和甲醛作为目标污染物,采用预处理后的凹凸棒石(Palygorskite,简称：PG)为催化剂载体,负载金属氧化物、尖晶石型氧化物、钙钛矿型氧化物为催化剂,进行了甲苯和甲醛的催化氧化过程研究且对催化剂制备过程进行了优化；并进一步对优选后催化剂的催化氧化动力学机理进行了剖析。研究首先对凹凸棒石载体进行了提纯,提纯后可以得到纯度较高的凹凸棒石粘土,透射电镜镜检和X射线衍射显示无明显杂质且凹凸棒石晶束得到了有效的分散。以提纯后的凹凸棒石作为催化剂载体,用浸渍法、共沉淀法和机械混合法等方法负载了铜、锰金属氧化物、尖晶石型氧化物、钙钛矿型氧化物等活性组分；并通过XRD、BET、TEM、TPR、抗压强度等手段对本文制备的一系列催化剂进行了表征：TEM结果表明用浸渍法和共沉淀法制备的催化剂活性组分以纳米级颗粒均匀分散在凹凸棒石载体的表面,用机械混合法制备的钙钛矿型催化剂活性组分粒径约为50～200nm。XRD结果显示金属氧化物以非晶体的形式负载在凹凸棒石载体的表面,催化剂经过不同温度的煅烧在载体上有尖晶石型化合物与钙钛矿型化合物形成,这两种化合物的形成对甲苯和甲醛的去除均有重要影响；抗压强度测定结果显示共沉淀法制备的钙钛矿型催化剂颗粒强度>16N,而机械混合法制备的钙钛矿型催化剂随着活性组分负载量的增加抗压强度呈减小趋势,当负载量达到40%时,抗压强度降为8.6N。用共沉淀法可使Cu和Mn氧化物在凹凸棒石表面形成纳米结构的复合金属氧化物催化剂,这种催化剂对甲苯有良好的催化氧化作用,助剂Ce的加入能促进铜锰尖晶石结构的形成并能提高甲苯的转化率,通过实验确定Ce/Cu=0.3且催化剂500℃煅烧后对甲苯的去除率最高,6%CuMn2Ce0.3/PG-500在288℃时甲苯转化率可以达到99%。用共沉淀法可制备纳米结构的La1-xSrxMnO3/PG钙钛矿型催化剂,催化剂经过700℃煅烧后凹凸棒石载体出现非晶化现象而棒状形貌依旧保持。掺杂量x=0～0.3和活性组分La1-xSrxMnO3负载量为3%～11%时随着锶掺杂量的增加和负载量的增加甲苯的转化率随之增高,9%La0.7Sr0.3MnO3/PG催化剂对甲苯完全转化温度(T99)为285.3℃,继续增加锶掺杂量和负载量催化剂活性变化不明显,另外应保持催化氧化反应体系中氧气含量在5vol.%以上以维持反应系统所需的氧气量。在9%La0.7Sr0.3MnO3/PG催化剂的100h稳定性实验中,甲苯转化率保持在95%以上且较为稳定。用机械混合法制备的La1-xSrxMnO3/PG活性组分以微米级别分散于PG表面,当x=0.3时30%La0.7Sr0.3MnO3/PG催化剂甲苯完全转化温度(T99)为302.7℃,高于共沉淀法制备的催化剂约17℃。尖晶石型6%CuMn2Ce0.3/PG-500催化剂和共沉淀法制备的钙钛矿型催化剂9%La0.7Sr0.3MnO3/PG催化氧化甲苯的动力学研究结果表明：简单的级数动力学模型不适合描述甲苯催化氧化反应的动力学过程,而Mars and Van Krevelen Model (MVK)动力学模型适合描述甲苯催化氧化反应的动力学过程,甲苯在催化剂6%CuMn2Ce0.3/PG-500和9%La0.7Sr0.3MnO3/PG上的催化氧化反应是基于氧化-还原机理进行的。甲苯在催化剂6%CuMn2Ce0.3/PG-500上的活化能(表面还原活化能17.26kJ/mol和表面氧化活化能23.62kJ/mol)小于催化剂9%La0.7Sr0.3MnO3/PG上的反应活化能(22.77kJ/mol和30.54kJ/mol),证明了甲苯的氧化反应在6%CuMn2Ce0.3/PG-500催化剂上更容易发生。用Cu、Mn金属氧化物和尖晶石型以及钙钛矿催化剂催化氧化甲醛同样有明显的效果,6%CuMn2Ce0.5/PG-500在179.3℃时甲醛转化率为99%,助剂Ce的添加同样有促进甲醛转化率的作用,与催化氧化甲苯不同的是Ce与Cu的最佳比例为0.5。当La0.7Sr0.3MnO3钙钛矿作活性组分负载在凹凸棒石上的比例为0.14时,195.7℃时甲醛的转化率为99%,继续增加钙钛矿活性组分比例甲醛转化率增加不明显。更多还原

【Abstract】 VOCs (Volatile Organic Compounds) is one of major gaseous pollution emissions in many industrial processes. It is a mostly promising approach for catalytic oxidation, by which VOCs can be degraded into CO2and H2O at low temperatures. However, the undefined typical pollutants removal mechanism restrict the high active and patience catalyst to the industrial applications of catalytic oxidation. To solve the problem, toluene and formaldehyde are taken as the target pollutants, while pretreatment palygorskite(PG) as catalyst support, loaded metal oxides(MOC),, spinel-type oxide(STC) or perovskite-type oxide(POC) as the activity components(AC). A study has been carried on catalytic oxidation process of toluene and formaldehyde as well as the catalyst optimition. Thus the kinetic mechanism of the optimized catalytic oxidation is also going to be suggested.PG is purified to get high purity catalyst support. It shows no obvious impurities, but PG crystal beams with effectively dispersion exist characterized by transmission electron microscope and X-ray diffractions. A series catalysts loaded on the Cu, Mn MOC, SOC and POC respectively were prepared by impregnation、hydrolysis coprecipitation and mechanical mixing methods. The catalysts were characterized by means of XRD, BET, TEM, TPR and compressive strength test. TEM results show that AC loaded by impregnation and coprecipitation are uniformly dispersed in the surface of PG. Othwise, the particle size of mechanical mixed AC in the POC is50～200nm. It is indicated PG-supported MOC, STC and POC are synthesized by calcination under different temperatures from XRD patterns. STC and POC play important effects on the removal of toluene and formaldehyde. The compressive strength test simultaneously demonstrates that the particle strength of POC prepared by coprecipitation is more than16N, while the POC prepared by mechanical mixing tend to weaken with the increase of AC. When the loaded wt%ratio reached40%, the compressive strength decreased to8.6N. It is through hydrolysis coprecipitation method that MOC can be made with nano structure in PG surface. Obviously MOC have promising catalytic oxidation for toluene, moreover the addition of Ce will promote the formation of copper manganese spinel’s structure and also improve the conversion of toluene. The results prove that when Ce/Cu=0.3, the catalyst annealed at500℃has the highest removal rate of toluene,99%toluene can be removed by6%CuMn2Ce0.3/PG-500at288℃. Coprecipitation can be used to get the nano-structral La1-xSrxMnO3/PG POC after calcination at700℃, which exhibits amorphous phenomenon on PG, but remains the rod morphology when doped amount x=0～0.3and La1-xSrxMnO3is up to3%～11%. The conversion of toluene increases with the increase of doped strontium and amount of capacity,9%La0.7Sr0.3MnO3/PG catalyst transformations toluene completely with the temperature (T99) of285.3℃, and catalystic activity changes unconspicuously when a further increase of doped strontium and AC. In addition, the oxygen content in the catalytic oxidation reaction system should be kept above5vol%, in order to maintain the amount of oxygen required by the reaction system. In the stability experiments of9%La0.7Sr0.3MnO3/PG catalyst for100h, a relatively stable95%toluene conversion can be obtained. Micrometer-level La1-xSrxMnO3/PG made by mechanically mixing is established to be dispersed in PG surface when x=0.3. The temperature(T99) of30%La0.7Sr0.3MnO3/PG catalyst for a complete toluene conversion is302.7℃, with a promotion of17℃for that of the coprecipitated catalysts..Several steps are used in the kinetic study of toluene catalytic oxidation with. a POC(9%La0.7Sr0.3MnO3/PG) and a STC(6%CuMn2Ce0.3/PG-500). The kinetic results show that:the simple series Model is not suitable for describing toluene catalytic oxidation reaction kinetics, while Mars and Van Krevelen Model (MVK) Model is more suitable. The catalytic oxidation reaction of toluene in both catalysts is based on oxidation-reduction mechanism. The activation energy (surface reduction activation energy17.26kJ/mol and surface oxidation activation energy23.62kJ/mol) of toluene in the STC is less than that (22.77kJ/mol and30.54kJ/mol) of the POC, which proves that the reaction is more likely to occur in the STC.MOC, STC and POC have substantial advantage on catalytic oxidation of formaldehyde as well. A99%conversion rate of formaldehyde is performed at179.3℃for6%CuMn2Ce0.5/PG-500, the effect of doped Ce also has been proved in the promotion in formaldehyde conversion rate. However the favorable doped ratio of Ce and Cu is0.5, which is different to the toluene catalytic oxidation. A0.14ratio of La0.7Sr0.3MnO3perovskite to PG can substantially improve the conversion of formaldehyde to99%at195.7℃. In spite of this, experimental results demonstrate that a further increase of AC ratio will bring little promotions.更多还原