【作者】 唐磊；

【导师】 鲍卫仁；

【作者基本信息】 太原理工大学 ， 化学工艺， 2011， 硕士

【摘要】 随着全球能源危机的加剧,动力性更强、经济性更好的柴油车和贫燃汽油车的使用量大大增加。在燃烧过程中加入过量空气,既提高了燃油的经济性,同时也显著降低了碳氢化合物(HC)和CO的排放量。但在富氧条件下,利用常规的三效催化剂很难有效地脱除NOx。因此,如何在贫燃条件下催化净化NOx已成为当前必须面对的问题。选择性催化还原NOx的反应中,要求催化剂不仅具有热稳定性好、使用寿命长的特点,而且需要再含有大量水分的湿热气氛中依然可保持良好的催化活性。催化剂的载体性能对催化剂的活性和使用寿命影响较大。汽车发动机的实际工况要求车用催化剂的载体必须满足,排气阻力小、升温快、耐高温、低热膨胀系数、高机械强度、质量轻、安装方便等条件。基于此,本文选择堇青石为催化剂载体,以氧化铜为铜源,采用一步水热合成法制备了Cu-SAPO-34/堇青石整体式催化剂。采用XRD、SEM、TG-DTG、ICP、XPS等手段对催化剂进行了表征,模拟实际柴油车和贫燃汽油车尾气的操作条件,分别以丙烷和氨气作为还原剂,评价了整体式催化剂的脱硝(deNOx)性能。通过实验研究得到以下几方面的结果：(1)一步水热合成法在合成分子筛时将硅源和杂原子源同时加入到合成体系中,使得杂原子可以进入到分子筛的骨架中,明显提高分子筛中杂原子的含量。一次合成的Cu-SAPO-34分子筛在堇青石载体上的负载量可达到22%左右。堇青石蜂窝陶瓷载体表面的Cu-SAPO-34分子筛与其结合具有一定的牢固度,超声波处理60min后,催化剂的损失率低于1%。(2)制备的整体式催化剂对柴油机车尾气表现出较高C3H8-SCR的脱硝活性。适当增加C3H8浓度、降低O2浓度或空速都有利于NOx-SCR活性的提高。在原料气中添加10%的水蒸气后,NOx转化率降低,加水停止后,催化剂活性可部分恢复。在NH3-SCR中,活性组分铜的添加对催化剂的催化活性有明显的促进作用。空速的降低有利于NOx-SCR活性的提高,但其对催化剂的活性影响并不明显。向原料气中添加大量的水蒸气,在一定程度上抑制了催化剂的活性,但若同时存在少量的SO2气体,则在一定程度上促进了催化剂活性的提高。(3)催化剂经过热处理之后,其晶体结构和表面性质基本没有发生变化。在550℃下,经过25小时的实验,催化剂仍然能够保持较高的催化活性和水热稳定性,整个反应时间内NOx的转化率都保持在80%以上更多还原

【Abstract】 As global energy crisis intensifying, the amounts of vehicles with stronger motive power and better economic performance increase gradually. The addition of excess O2 not only improve the efficiency of fuel but also significantly reduce the emissions of HC and CO. But NOx, which is the main environmental pollutant, is purified difficultly by the conventional three-way catalysts in the rich oxygen conditions. Recently, the catalytic conversion of NO in the presence of excess O2 has been intensively studied to decrease the NOX in the exhaust gas from diesel engines and lean-burn facilities.The catalyst for NOX-SCR needs to meet the demands of resist-thermal and long-life but also exhibits high activity for the selective reduction of NO under an atmosphere containing water vapor and rich O2. Catalyst carrier properties have the great effect on catalyst activity and service-life. Due to the influence of actual conditions of engine, vehicle exhaust catalyst carrier must have the traits of small resistance, warming faster, high temperature resistance, high mechanical strength, light quality, convenient installation, and et al.Based on these, the cordierite monoliths were used as the catalyst carriers, CuO was used as the copper source and Cu-SAPO-34/cordierite samples were synthesized via one-step hydrothermal procedure. The samples were characterized by XRD, SEM, TG-DTG, ICP, XPS techniques. The performance of Cu-SAPO-34/cordierite monolithic catalysts for removal NO in simulated diesel-engine exhaust conditions was explored using propane and ammonia as the reducing agent, respectively. The main results and conclusion obtained from experiments and studies were given as follow:(1) The method of one-step hydrothermal procedure can make the metal active components directly synthesize on the molecular sieve and obviously increasing the content of miscellaneous atoms of molecular sieve. The loading amount is more than 22% after one synthesis operation. The Cu-SAPO-34 coatings obtained by the in situ synthesis are firm and compact. The loss of the catalysts is lower than 1% after ultrasonic treatment.(2) For the C3H8-SCR process, Cu- SAPO-34/cordierite catalyst shows a high conversion of NO. NO conversion decreases with the increase of space velocity and the decrease of concentration of O2. The NOx conversion decreases after the addition of 10% water vapor to the feed gas but the deactivation caused by water vapor is not permanent. For the NH3-SCR process, the active Cu component prepared through in situ synthesis can significantly improve the activity of selective catalytic reduction. The conversion of NO is decreased slightly with the increase of space velocity. The H2O in the feed gas decreases the NO conversion and the coexistence of SO2 and H2O have the slight promoting influence on the NO reduction activity. (3) The aging experiments clearly show that almost no changes of the characteristic diffraction peaks can be recognized in XRD patterns of catalysts before and after the heat treatment. Cu-SAPO-34/cordierite shows the good thermal and chemical stability. The conversion of NOX is more than 80% in the entire experimental periods.更多还原