【作者】 金瑞奔；

【导师】 吴忠标；

【作者基本信息】 浙江大学 ， 环境工程， 2010， 博士

【摘要】 氮氧化物是危害大气的主要污染物之一,使用选择性催化还原(SCR)技术是脱除固定源排放烟气中NOx的有效方法之一。近年来低温SCR技术由于具有节能减耗和运行成本低的特点正得到越来越多研究者的关注。从国内外低温SCR技术的研究现状来看,该技术工业化的主要障碍是低温范围内活性不高、催化剂抗SO2毒化性能差、反应机理和SO2中毒机理不明确等问题。针对以上问题,本文使用以锰氧化物作为主要活性成分的催化剂,对其低温SCR脱硝性能进行了较为系统的研究。本文首先对Mn/TiO2催化剂进行金属元素掺杂改性,通过活性实验和分析测试表征结果发现,Ce掺杂可以大幅度提高催化剂的低温SCR活性(100℃时的催化活性从62%提高到95%左右),Ce的加入能够增强催化剂的储氧能力和表面酸性,促进NH3在催化剂表面的吸附和活化。在此研究基础上,本文使用上述Mn-Ce复合氧化物作为催化剂的活性组分,分别选择了TiO2、Al2O3、ZSM5和活性炭作为催化剂的载体,考察了这几种负载型催化剂的SCR活性,结果发现TiO2和Al2O3负载后的催化剂在低温下SCR活性较高。本文还研究了这两个负载型催化剂的低温SCR反应机理,发现在这两个催化剂上进行的SCR反应均存在多个反应途径。而由于TiO2和Al2O3载体性质的差异会导致各种反应途径在这两个负载型催化剂上所占比例不同。其中Mn-Ce/TiO2上以吸附态的配位铵和气相NO反应为主,而Mn-Ce/Al2O3催化剂上发生SCR反应时主要先进行NO的氧化反应,然后该氧化产物再和NH3之间发生反应完成整个SCR反应。此外,本文还较系统地考察了SO2在低温条件下对Mn/TiO2和Mn-Ce/TiO2催化剂SCR活性的影响,同时对SO2的影响机理进行了研究,发现Mn/TiO2催化剂在SO2反应气氛中失活很快,硫铵盐的沉积和活性组分的硫酸化是催化剂失活的重要原因；Ce的加入可以有效地抑制催化剂活性组分的硫酸化,同时还能降低硫酸盐在催化剂表面的稳定性从而可以提高催化剂的抗硫性。最后,本文研究了低温SCR反应中SO2浓度、水汽浓度、反应温度等工艺参数对催化剂活性的影响,为该技术的工业化应用提供基础数据。重点研究了反应温度对Mn-Ce/TiO2催化剂的影响,发现较低的反应温度可以缓解催化剂活性组分的硫酸化,减缓催化剂的失活。在此基础上对催化剂进行各种再生处理,发现通过简单的水洗过程可使催化剂的绝大部分活性得以恢复。通过本文的系统研究,开发了一种新型的Mn-Ce/TiO2复合氧化物低温SCR催化剂,与现有报道的SCR催化剂相比,该催化剂在低温条件下的催化活性高、抗SO2毒化能力强,为低温SCR工艺实现工业化应用奠定了基础。此外,还探明了在此类催化剂上进行的SCR反应的反应机理以及SO2对催化剂的毒化机理,为今后低温SCR催化剂的进一步改进提供了指导。更多还原

【Abstract】 NOx is one of the main air pollutants and selective catalytic reduction (SCR) is an effective way to remove NOx in the flue gas from stationary sources. Recently, low-temperature SCR process has attracted more and more interests for its low energy consumption and operating cost. Based on the review of the current situation of SCR technology, it was pointed out that the following shortcomings are the main obstacle of the industrial application of the low-temperature SCR technology:low activity at low temperature, poor SO2 resistance of catalysts and uncertainty of reaction and SO2-poisoning mechanisms. In order to solve these problems, the low-temperature SCR reaction was systematically investigated by using MnOx based catalysts in this dissertation.Firstly, several metals were chosen to be doped into Mn/TiO2 catalyst. From activity tests and characterization results, it was found that Ce doping could greatly enhance the low-temperature SCR activity of the catalyst (the activity was enhanced from 62% to 95% at 100℃). The oxygen storage capacity and the surface acidity of the Mn/TiO2 catalyst were improved by the introduction of Ce, which would be beneficial to the adsoroption of NH3 and its activitation.Secondly, Mn-Ce oxides were supported on TiO2, Al2O3, ZSM5 and active carbon respectively. From the comparison results of these catalysts’activity, it was found that Mn-Ce/TiO2 and Mn-Ce/Al2O3 had relatively higher low-temperature SCR acivity than other supported samples. The SCR reaction mechanism of these two catalysts was then studied and the results indicated that there were several reaction paths for both of the samples and these reaction paths made different concentrations to the SCR activity of two catalysts because of the property differences between TiO2 and Al2O3. For Mn-Ce/TiO2 catalyst, the SCR reaction mainly took place between adsorbed NH3 species and gas-phase NO, while in the case of Mn-Ce/Al2O3, the SCR reaction commenced with NO oxidation, then its oxidation products reacted with NH3 to carry out SCR reaction.Fuethemore, the effects of SO2 on the SCR activity of Mn/TiO2 and Mn-Ce/TiO2 catalysts as well as its mechanism were investigated detailedly. A serious deactivation by SO2 was detected on Mn/TiO2 catalyst. The deposition of ammonium sulfate species on catalyst surface and the sulfation of catalyst active phase were proved to be the main reasons for the catalyst deactivation in the presence of SO2 during SCR reaction. Ce doping could effectively inhibit the sulfation of catalyst active phase and decrease the stability of the formed sulfate species. Finally, the relationship between SCR activity of Mn-Ce/TiO2 catalyst and operating parameters such as SO2 and H2O concentrations, reaction temperature, was investigated to provide possible guidances for industrial application. Especially the effects of reaction temperature on catalyst activity were studied in detail and the results suggested that low reaction temperature could relieve the sulfation of catalyst active phase and the deactivation by SO2. The deactivated samples were regenerated by different treatments and it was found that water-washing could effectively recover the most catalyst activity.更多还原