【作者】 林探厅；

【导师】 余倩；

【作者基本信息】 广东工业大学 ， 化学工程， 2011， 硕士

【摘要】 目前,在众多有机废气处理技术中,催化燃烧法是消除挥发性有机化合物（VOCs）污染最有效方法之一,具有设备简单,能耗低,消除效果好等特点,而催化剂是催化燃烧法消除VOCs的关键。本文用堇青石蜂窝陶瓷做第一载体,以贵金属Pd为活性组分,用化学镀法制备了一系列Pd负载型整体式催化剂。以甲苯和甲醛的催化燃烧作为作为考察催化剂的探针反应,考察了催化剂的催化活性和耐高温性,并采用多种方法对催化剂进行表征,将催化燃烧性能与催化剂表面性质进行了关联以及进行了催化机理的探讨。本文的主要研究内容和结果如下：催化剂的制备。采用化学镀法制备Pd/堇青石陶瓷整体式催化剂,通过实验确定了化学镀的最佳反应条件：PdCl₂:0.05-0.5g/L, NH₃·H₂O （25%）:40-120g/L, NH4Cl: 5-20g/L, NaH₂PO₂·H₂O:1-10g/L, HCl（36-38%）:1-4mL/L, pH:9-10,温度：25℃-60℃。研究表明,采用化学镀制备技术可在堇青石陶瓷载体直接负载Pd颗粒,有利于提高钯的利用率,工艺简单,制备周期短。催化剂的表征及活性评价。采用SEM、XRD、UV、EDX、BET、XPS、H₂-TPR、O₂-TPD等手段对整体式催化剂的表面形貌、结构和性能进行表征。通过SEM和EDX的测定,可知Pd晶粒均匀地负载在堇青石陶瓷载体。以甲苯和甲醛作为VOCs的代表污染物,进行催化燃烧处理,对催化剂进行活性评价,研究表明,当活性组分Pd负载量在0.36wt%以上时具有较高的催化活性,对于不同焙烧温度下制备的Pd/堇青石陶瓷整体式催化剂,500℃焙烧下的具有相对较高的催化活性,Pd晶粒在载体表面上均匀负载,晶粒大小均一,范围在100nm左右。之后随着焙烧温度（高于500℃）的升高,催化活性逐渐降低,主要与活性物种PdO颗粒的长大、烧结、晶格氧的减少和比表面积的减小有关。研究了空速、有机废气中甲苯和甲醛的浓度和稳定性等因素对Pd/堇青石陶瓷整体式催化剂催化燃烧性能的影响。实验表明,随着空速的增大,催化剂对甲苯和甲醛的催化处理效率都逐渐降低。催化剂在空速20000h-1以内时,具有较高的甲苯催化处理效率；在3000h-1空速内时,对甲醛具有较高的催化处理效率；对于甲苯,甲苯浓度对催化燃烧处理效率影响较小,在6.0g/m3以内都具有较高的催化处理效率；对于甲醛,甲醛浓度在2.0mg/m3范围内时,催化剂才对其具有较高的处理效率,说明甲醛浓度对催化燃烧处理效率的影响较大,表明有机污染物的种类和浓度对催化处理效率有较明显影响,这也说明催化剂具有选择性。在甲苯催化燃烧的寿命实验中发现,在10h之内,Pd/堇青石陶瓷整体式催化剂的甲苯催化处理效率一直保持在99%左右,之后催化处理效率随着反应时间逐渐下降。重新焙烧再生的催化剂,在9h内甲苯催化处理效率可保持在99%,说明催化剂可多次再生循环使用。研究还探讨了采用浸渍法在堇青石载体上负载一层CeO₂-ZrO₂复合物后,再采用化学镀负载上活性组分Pd,制备Pd/Ceo.gZro.202/堇青石陶瓷整体式催化剂,并采用SEM、EDX、UV漫反射对其进行表征。研究表明,该类催化剂具有良好的催化活性和耐高温性。相对于Pd/堇青石整体式催化剂,与500℃焙烧的催化剂相比,800℃焙烧的Pd/堇青石整体式催化剂,T99%为255℃,提高了25℃。800℃焙烧的0.36wt%Pd/Ce0.8Zr0.202/堇青石陶瓷整体式催化剂,T99%为250℃,与500℃焙烧的催化剂相比,只提高了15℃,主要可能是CeO₂-ZrO₂复合氧化物具有贮氧池的作用,可以向Pd提供品格氧,抑制了PdO晶粒的烧结,该催化剂是具有较好的催化活性的。更多还原

【Abstract】 Among the technologies developed for the treatment of VOCs, catalytic combustion is considered to be one of the most effective measures to destroy VOCs due to its simple equipment and eliminating VOCs at relatively low temperatures. The catalyst is the key of catalytic combustion. Cordierite honeycomb ceamics was the carrier, precous metal palladium was the active componet, the Pd-based monolithic catalyst was prapared by electroless plating. The catalytic activity behavior and thermal stability of the monolithic catalysts for toluene were investigated. In addition, the Pd-based monolithic catalysts were charactrized by various techniques, and the mechanism of catalytic oxidation was also studied. The main contents and results in the thesis could be summarized as follows:Preparation of the catalysts. Pd/cordierite monolithic catalysts were prepared by electroless plating. The experiment showed that the most optimum conditions of electroless plationg were:concentration of PdCl₂ was form 0.05g/L to 0.5g/L, concentration of NH₃·H₂O （25%） was form 40g/L to 120g/L, concentration of NH4C1 was form 5g/L to 20g/L, concentration of NaH₂PO₂·H₂O was form 1g/L to 10g/L, concentration of HC1 （36-38%） was form 1g/L to 4mL/L, pH was 9 to 10, reaction temperature was form 25℃to 60℃. The results showed that palladium nanoparticles were dispersed symmetrically over cordierite, by using this technology, it had the advantages of simple equipment, easy process of manufacture, high utilization of palladium, short period of preparation, low cost, etc.Characterization and catalytic activity evaluation. The surface morphology, structure and performancethe of the Pd-based monolithic catalysts were charactrized by SEM, XRD, UV, EDX, BET, XPS, H₂-TPR and O₂-TPD techniques. The palladium grains were load evenly on the cordierite ceramic substrate. Toluene and formaldehyde were instead of VOCs in the experiment of catalytic activity evaluation. The experiment showed that the catalysts showed more activity when the loading of active component palladium loading over 0.36wt%. The Pd-based monolithic catalysts were prepared under different calcination temperatures, the one prepared under 500℃showed more activity and the palladium grains size were about 100nm, then it was found the efficiency became lower with the rise of calcination temperature, this result might be attributed to the sintering and decomposition of the PdO particles and decrease in the surface area.It was also studied the influence of space velocity, concentration of VOCs and the temperature. It was found that the efficiency of catalytic combustion for toluene and formaldehyde became lower when space velocity became faster. It had a higher catalytic efficiency of toluene when space velocity under 20000h-1. But space velocity was form under 3000h-1, the monolithic catalyst had a high activity for formaldehyde. It was also found that concentration of toluene had weak influence to the catalytic combustion, the monolithic catalyst had high activity when concentration of toluene within 6.0g/m3. It had high activity when concentration of formaldehyde within 2.0mg/m3, this showed that concentration of formaldehyde had strong influence to catalytic combustion. So elements of VOCs had greater impact to the catalytic combustion, this also showed that the catalyst has selectivity. In the Catalytic combustion process, toluene catalytic efficiency of Pd/cordierite monolithic catalyst was maintained at about 99% within 10h in the endurance test, then catalytic efficiency decreased with the reaction time after 10h, mainly because PdO-Pd redox cycle could not be proceed smoothly, most of PdO was reduced to Pd0 by toluene molecule, led to the amount of PdO were not enough, therefore activity decreased.CeO₂-ZrO₂ mixed oxides were investigated due to their excellent oxygen storage capacity, high thermal stability. CeO₂-ZrO₂ mixed oxides were loaded on the catalyst support, and then active component palladium was plated by electroless plating. Meanwhile the washcoats and their supported-Pd catalysts were characterized by SEM, EDX and UV. In addition, it was studied the influene of palladium loading and calcination temperature. It showed that these catalysts had good catalytic activity and temperature resistance. Relative to the Pd/cordierite monolithic catalyst, compared to the catalyst calcined at 500℃, T99% of the catalyst calcined at 800℃was 255℃, increasing by 25℃. Compared to the monolithic catalyst calcined at 500℃, T99% of the monolithic catalyst calcined at 800℃was 250℃, increasing by 15℃. The main reason was that CeO₂-ZrO₂ mixed oxides could act as oxygen storge resercor giving lattice oxygen to Pd, which could stabilize PdO at high temperatures.更多还原