【作者】 张金桥；

【导师】 李瑞丰；

【作者基本信息】 太原理工大学 ， 工业催化， 2007， 博士

【摘要】 煤、石油、天然气等物质的燃烧满足了人类对于能源的需求，但排放的燃烧尾气造成了严重的环境污染，SO₂，NO_x（90％为NO），CO，CO₂等污染物的排放对人类的生存环境产生了极大的威胁。尤其是NO_x不仅能形成酸雨和光化学雾，而且能引起温室效应，人类的很多疾病都或多或少与NO_x的排放有关。如何有效地消除尾气中的NO_x是一项世界性的难题，尽管NH₃作还原剂选择还原NO_x在固定源（发电厂）NO_x等行业已经投入商业运营，但由于NH₃容易泄漏、腐蚀性强、设备投资大、操作难度高、能形成硫酸铵等造成管道堵塞，将该技术应用于移动源NO_x（汽车尾气）的治理几乎是不可能。三效催化剂（TWC）应用于汽车等移动源尾气时能同时脱除尾气中的CO，HC和NO_x，但该技术只能应用在空燃比（A/F=14.6）附近狭窄的范围内。富氧燃烧是当前提倡节约能源和减少废气排放的发展趋势，而TWC催化剂在这种燃烧条件下对脱除NO_x基本没有活性。碳氢化合物为还原剂选择催化还原NO_x（HC-SCR）是目前研究非常热门的课题，自从发现CH₄能选择催化还原NO（CH₄-SCR），CH₄-SCR被认为是最具应用前景的脱除氮氧化物技术。选择具有高活性、选择性和抗SO₂和H₂O毒化性能的催化剂是将该技术投入实际应用必须首先解决的课题，正是在上述研究背景下提出了本论文的研究课题。本文首次采用了一种具有FAU和BEA两种拓扑结构的复合沸石分子筛（FBZ）为载体，系统的研究了Co和Mn交换FBZ催化剂（CoH-FBZ和MnH-FBZ）催化CH₄还原NO的催化性能，并应用XRD，FT-IR，DRS-UV-Vis，SEM，NH₃-TPD，H₂-TPR等现代的分析技术对催化剂进行了表征，采用NO，NO+O₂，NO₂吸附和程序升温脱附的方法研究了N、O的吸附态与催化剂表面的相互作用。考察了复合结构催化剂的抗H₂O和SO₂毒化性能，采用SO₂-TPSR技术对比研究了SO₂毒化单一结构催化剂CoH-Beta和复合结构催化剂CoH-FBZ表面形成的含硫物种与催化剂表面之间的相互作用。并对传统催化剂CoH-ZSM-5的催化性能进行了研究，应用NO，NO+O₂，NO₂，NO+NO₂吸附和程序升温脱附技术对氮氧化物与催化剂CoH-ZSM-5表面的相互作用进行了研究，以期获得具有应用价值的催化剂，并探讨CH₄-SCR反应的机理。研究结果表明沸石分子筛的拓扑结构直接影响催化剂的CH₄-SCR性能，催化剂抗SO₂和H₂O的毒化性能也与沸石载体的拓扑结构有关。本论文主要取得了以下几方面研究进展：（一）Co，Mn系列复合结构催化剂CH₄-SCR的研究结果1采用两步水热晶化法能成功的合成具有FAU和BEA复合拓扑结构的沸石分子筛FBZ，FBZ的XRD图中仅观察到FAU和BEA两种拓扑结构的特征衍射峰且没有其它杂晶峰，应用XRD结果可获得复合结构沸石中两种拓扑结构的质量相对含量；FBZ的FTIR图谱中能观察到FAU和BEA两种拓扑结构的特征吸收峰，两种拓扑结构吸收峰的相对强度与XRD图一致；FBZ的SEM图中没有观察到八面体型（典型FAU的晶型晶貌），为均一椭球型的晶型晶貌，由于BEA结构生长在FAU结构的外表面，因此FBZ的SEM图与单一Beta沸石的SEM图较为相近。2 NH₃-TPD结果表明，H-FBZ上产生了一种新的强酸位，该强酸位能够被金属离子交换，且Co，Mn离子交换后该酸位的平均酸强度有所增强。程序升温氧化（TPO）和H₂程序升温还原（H₂-TPR）研究结果表明，处于离子交换位置的Co，Mn对氧化和还原处理不敏感，在所研究的选择催化CH₄还原NO过程中能保持氧化态不发生变化。3 CoH-FBZ催化剂的DRS-UV-Vis图谱与单一结构催化剂CoH-Beta和CoH-Y的DRS-UV-Vis图谱存在一定的差异，结合NH₃-TPD和复合沸石分子筛的结构特点，可以推断在CoH-FBZ中产生了新Co位，氮氧化物在催化剂表面的吸附支持这一推论。4研究结果表明复合结构催化剂CoH-FBZ与机械混合催化剂（CoH-Y+CoH-Beta）存在显著的差异，催化剂的CH₄-SCR催化性能受沸石分子筛的拓扑结、沸石分子筛中的酸位、金属性质、金属的所处的晶体场、反应条件等因素的影响。具体如下：a．催化活性测试结果表明，与CoH-Beta和CoH-Y单一拓扑结构机械混合催化剂相比，负载Co的复合结构催化剂CoH-FBZ上NO还原为N₂的转化率明显较高，且当BEA的质量相对含量为60-80％时，复合结构催化剂显示出较高的催化活性和CH₄选择性；催化剂的催化活性随着其中Co含量的增大而提高，高空速使NO还原为N₂的转化率下降；沸石分子筛载体的酸性能促进CH₄-SCR反应进行；O₂能促进CoH-FBZ催化剂催化CH₄还原NO，当反应体系中无O₂时，CH₄还原NO的活性很低(2180×10^-6NO+2050×10^-6CH₄)，随着反应气流中O₂的浓度增大（反应温度773 K），CH₄还原NO的催化活性迅速增大，当O₂的浓度为2.00％时，催化活性达到极大，继续提高O₂的浓度催化剂的催化活性有所下降。O₂的主要作用是能与NO在催化剂表面形成能活化CH₄的中间吸附态-NO_y，然而过高的O₂浓度使CH₄直接燃烧速率加快，从而抑制了SCR反应的进行。反应体系中存在H₂O或SO₂时，催化剂的催化活性明显下降，两种毒化物质同时存在使催化剂中毒更加严重，但复合结构催化剂较单一结构催化剂显示出更好的抗H₂O或SO₂毒化性能。b．Mn系列复合结构催化剂的催化性能与Co系列复合结构催化剂的催化性能非常类似，与MnH-Beta和MnH-Y单一拓扑结构机械混合催化剂相比，负载Mn的复合结构催化剂MnH-FBZ上NO还原为N₂的转化率明显较高，且当BEA拓扑结构的质量相对含量为60-80％时，复合结构催化剂显示出较高的催化活性和CH₄选择性；催化剂的催化活性随其中Mn含量增大而提高；沸石分子筛载体的酸性能促进CH₄-SCR反应进行。同样，复合结构催化剂较单一结构催化剂显示出更好的抗H₂O或SO₂毒化性能。c．单一拓扑结构沸石分子筛为载体时，Co系列催化剂的催化活性较Mn系列催化剂的催化活性高，但复合结构催化剂MnH-FBZ催化剂的催化性能与CoH-FBZ的催化性能基本相同，在一定的反应条件下，MnH-FBZ的催化活性甚至较CoH-FBZ的催化活性高。进一步证实所制备的复合结构催化剂并非单一结构催化剂的简单机械混合，且沸石分子筛载体对催化剂的CH₄-SCR活性起着很重要的作用。两类Mn系列催化剂均较Co系列催化剂显示好的抗H₂O毒化性能，但当反应体系中存在SO₂时，Mn系催化剂在抗毒化性能方面的优势被削弱。5 NO-，NO₂-和NO+O₂-TPD研究结果表明，载体对N、O化物与催化剂表面相互作用有很大的影响。NO-TPD结果表明催化剂表面形成的吸附态NO不稳定，在573 K前基本脱附完全，且CoH-FBZ系列催化剂上形成的吸附态NO相对更稳定。NO₂与NO+O₂能在催化剂表面形成稳定的含N、O的吸附态-NO_y。与单一拓扑结构的CoH-Beta和CoH-Y相比，CoH-FBZ表面形成的吸附态-NO_y相对更稳定，且NO+O₂（或NO₂）在CoH-FBZ表面吸附和程序升温脱附曲线上至少存在两个NO₂脱附中心。由于氮氧化物只能吸附在催化剂中的Co位上，表明复合结构催化剂中形成了一种新的Co位，由于复合结构的拓扑结构、强酸位和新Co位的协同效应使CoH-FBZ具有新的CH₄-SCR催化活性。6 SO₂-TPSR研究结果表明，被SO₂毒化后的催化剂表面形成了稳定的含硫化合物，含硫化合物占据部分的活性，导致催化剂表面形成活性吸附态-NO_y含量下降是SO₂使催化剂催化活性下降的主要原因。由于复合结构催化剂CoH-FBZ表面形成的含硫化合物相对于单一结构催化剂CoH-Beta表面形成的含硫化合物不稳定，提高反应温度更多含硫化合物脱附释放出部分活性位，使复合结构催化剂显示出较好的抗SO₂中毒性能。（二）CoH-ZSM-5催化剂CH₄-SCR的研究结果本论文中系统的研究了CoH-ZSM-5催化剂上的NO_x（O₂）-TPD，并研究了有氧和无氧条件下，CoH-ZSM-5上CH₄选择催化还原NO或NO₂。1研究结果表明在无氧条件下，CH₄选择催化还原NO的活性很低，加入O₂极大的提高了CH₄-SCR催化活性。在NO／CH₄／O₂和NO₂／CH₄／O₂反应体系中，CH₄还原NO和NO₂为N₂的转化率基本相同，CH₄的转化率也基本相同。而无氧体系反应NO₂／CH₄，673 K前CH₄还原NO₂的催化性能与有氧条件下相同，继续提高反应温度，CH₄还原NO₂为N₂的催化活性有所下降。2 TPD研究结果表明在CoH-ZSM-5表面形成的含N、O吸附态均吸附在催化剂中的Co位上，吸附量随催化剂中Co含量增大而增大，吸附条件对NO，NO₂和NO+O₂在催化剂表面形成的吸附态的量有很大影响。NO在催化剂表面形成的吸附态很不稳定，523 K前基本脱附完全，吸附过程中NO的浓度对催化剂表面形成NO吸附态的量影响不大；随着吸附温度上升，NO吸附态的量迅速下降。NO₂在催化剂表面形成的吸附态-NO_y的量随吸附过程NO₂浓度增大而增大，提高吸附过程的温度吸附态-NO_y的量则明显下降。尽管NO较-NO_y在催化剂表面的吸附弱，但NO与NO₂共吸附时，由于竞争吸附使吸附态-NO_y的量明显下降。3在1000×10^-6NO₂，1000×10^-6 NO+1000×10^-6NO₂和2000×10^-6NO+2％O₂三种吸附过程中，由于最后一过程NO₂的浓度最低，且存在NO的竞争吸附，因此，在催化剂表面形成的吸附态-NO_y的量应该最少，但实际形成吸附态-NO_y的量处于另外两种吸附过程形成吸附态-NO_y的量之间。这表明NO+O₂能不经过NO₂直接在催化剂表面形成吸附态-NO_y。4 O₂的主要作用是与NO在催化剂表面形成能活化CH₄的吸附态-NO_y，从而促进CH₄-SCR反应进行。更多还原

【Abstract】 The combustion of coal, petroleum and natural-gas etc. meets the mankind’s needs of energy. However, the emission of flue gas has caused serious environmental pollutions. SO₂, NO_x （NO accounts for 90%）, CO and CO₂ results in great threat to environment, particularly NO_x can not only lead to formation of acid rain and photochemical smog, but also to "green-house" effect. Many diseases are more or less related to NO_x. How to abate NO_x in the flue gas is a tough task in the worldwide. Although selective catalytic reduction of NO_x with NH₃ has been put into commercial application in the disposal of stationary source of NO_x such as emission gas in the electric power plant, application of this technology in the moving source of NO_x such as the traffic flue gas is impossible because of the well-known reasons such as storage and leakage of NH₃, costly equipment, strict operation conditions and formation of sulfate leading to pipe jam. Three-Way-Catalysts （TWC） is an effective way to abate CO, HC, and NO_x in the traffic flue gas simultaneously. However, this type of catalysts is only effective in the narrow range of air to fuel ratio adjacent to 14.6. Combustion of fuel in the presence of excess oxygen is not only an effective way to improve the fuel utilizing efficiency, but also can decrease the emission of pollutants. However, TWC catalysts exhibit low activity for NO_x reduction in these conditions. Selective catalytic reduction of NO_x with hydrocarbon （HC-SCR） is considered to be the potential technology substituting for NH₃-SCR, particularly selective catalytic reduction of NO_x by methane （CH₄-SCR）. Preparing catalysts with high activity, selectivity and SO₂ and H₂O tolerance should be solved before practical application of the CH4-SCR technology. The investigating tasks are put forward under this research background in this paper.A type of new zeolite composite FBZ with FAU and BEA topology structure was synthesized. Selective catalytic reduction of NO_x in the presence of excess oxygen was investigated systemically over the Co- or Mn- ion-exchange H-FBZ catalysts. XRD, FT-IR, DRS-UV-Vis, FE-SEM, NH₃-TPD, H₂-TPR techniques were applied to characterize the catalysts. Combined NO, NO+O₂、NO₂ adsorption and temperature programmed desorption （TPD） were applied to investigate the adsorption species contained N and O over the catalysts. The H₂O and SO₂ tolerance of the catalysts were also studied. SO₂ temperature programmed surface reaction （TPSR） was applied to investigate the sulfur species formed during the poisonous tests. CH₄-SCR was also investigated over the traditional catalyst CoH-ZSM-5. Combined NO, NO+O₂, NO₂ and NO+NO₂ adsorption and TPD were carried out over CoH-ZSM-5 to investigate the interaction of the N and O contained species with the catalyst surface. This paper would focus on acquiring novel catalyst, and valuable information for the reaction mechanism by which the CH₄-SCR occurs over Co-zeolite catalyst. It is found that the topology structure of the carrier strongly affects the catalytic properties of the catalysts. The SO₂ and H₂O tolerance of the catalysts is also affected by the carrier. The main research results obtained in this paper will be shown as follows:I) Research progresses of CH₄-SCR in the Co and Mn contained zeolite composite CoH-FBZ and MnH-FBZ1 Zeolite composite with FAU and BEA topology structure can be synthesized succefully with two step hydrothermal crystalyzing method. Only characteristic peaks of FAU and BEA topology structure are observed over the XRD patterns of FBZ. The relative content of the two kinds of topology structure can be obtained by the XRD results. Characteristic peaks of FAU and BEA topology structure are observed in the FTIR spectra of the catalysts. No octahedral morphology is observed in the SEM images of the zeolite composite, whereas it cannot be excluded completely. Homogenous ellipse morphology is observed in the SEM image of zeolite composite. The morphology is similar to that of the Beta zeolite because the zeolite composite FBZ is synthesized by overgrowing or epitaxially growing a layer of zeolite Beta on the pseudo-crystal of FAU zeolite.2 NH₃-TPD results show that a new kind of strong acidic sites is formed on H-FBZ. These acidic sites can be ion-exchanged by the metal ions. The average acidity of this type of acidic sites increases after ion-exchange of Co or Mn cations. Temperature programmed oxidizing （TPO） and temperature programmed reducing （TPR） results show that the ion-exchange Co and Mn cations in the zeolite are resist to the reducing and oxidizing process.3 Different DRS-UV-Vis spectra are obtained over CoH-FBZ, CoH-Y, CoH-Beta and the physical mixture of both. Combining the NH₃-TPD results and the properties of the zeolite composite, new ion-exchange Co sites could be formed in CoH-FBZ. The combined NO, NO+O₂ and NO₂ adsorption and TPD as shown in the follows support this viewpoint.4 It is found that the composite catalysts CoH-FBZ and the physical mixture catalysts of CoH-Y and CoH-Beta exhibit significant different properties. The topology structure of the carrier, acidity of the zeolite carrier, the metal cations and their ligand and the reaction conditions significantly affects the catalytic properties of the catalysts, which are discussed in detail as follows:a. Activity test results show that the catalytic activity is significantly affected by the topology structure of the catalyst. Compared to the physical mixture catalysts of CoH-Y and CoH-Beta, with comparable FAU and BEA topology structure, CoH-FBZ catalysts exhibit much higher catalytic activity, particularly the catalysts with the mass content of BEA topology structure between 60 % and 80%. CoH-FBZ catalysts also exhibit higher CH₄ selectivity than the physical mixture catalysts of CoH-Y and CoH-Beta. The catalytic activity increases with the cobalt content in the catalysts. Higher gas hourly space velocity （GHSV） results in lower NO to N₂ conversion. The acidity of the carrier can promote the CH₄-SCR. O₂ is another essential factor in the CH₄-SCR. In the reaction system absence of oxygen at 773 K, i.e. 2050×10^-6 CH₄/2180×10^-6 NO, the catalytic activity is very low in the whole test temperature range. Increasing the oxygen concentration, the NO to N₂ conversion increases significantly and reaches a maximum while the oxygen concentration is up to 2.00%. Further increasing the oxygen concentration, the catalytic activity decreases. O₂ can react with NO to form adsorbed -NO_y, species over the catalyst. Too higher oxygen concentration leads to the rate of direct CH₄ combustion increase quickly, and the CH₄-SCR is inhibited.In the presence of H₂O or SO₂, the catalytic activity of the catalyst decreases considerably. Co-existence of H₂O and SO₂, NO to N₂ conversion decreases further, whereas, the composite catalyst CoH-FBZ exhibits better H₂O and SO₂ than the catalysts CoH-Beta with single topology structure.b. Similar catalytic properties are obtained over MnH-FBZ and CoH-FBZ catalysts. MnH-FBZ catalysts exhibit much higher catalytic activity than physical mixture catalysts with comparable FAU and BEA topology, particularly over the catalysts with BEA topology structure mass content between 60-80%. The catalytic activity increases with the Mn content in the catalysts. As that in CoH-FBZ catalysts, the acidity of the catalyst promotes the CH₄-SCR activity. The composite catalyst MnH-FBZ exhibits better H₂O and SO₂ than the catalysts MnH-Beta with single topology structure.c. The CH₄-SCR activity over the Co ion-exchange catalysts with single topology structure is higher than that over the Mn ion-exchange catalysts with comparable metal content. However, the activity of the two types of composite catalysts is almost comparable on both kind catalysts. In some reaction conditions, the catalytic activity of MnH-FBZ is even higher than that of CoH-FBZ. These results illustrate that the zeolite composite exhibit different properties to the physical mixtures, and the CH₄-SCR activity is influenced by the topology structure of the zeolite singnificantly. Mn catalysts with either single topoloigy structure or composite topology structure better H₂O tolerance than Co catalysts, whereas addition of SO₂, the difference decreases.5 Combined NO, NO₂, NO+O₂ adsorption and TPD results show that the N and O contained species formed over the catalyst are significantly affected by the topology structure of the carrier. NO-TPD results show that the NO species formed over the catalysts is unstable and desorbed at temperature lower than 573 K. The NO species is adsorbed more strongly on CoH-FBZ catalysts. Compared with the CoH-Beta and CoH-Y with single topology structure, adsorbed -NO_y species formed by NO+O₂ co-adsorption （or NO₂ adsorption） is adsorbed more strongly on CoH-FBZ than on CoH-Y and CoH-Beta. Furthermore, at least two NO₂ desorption centers are observed over TPD profiles of CoH-FBZ. N and O contained species are only adsorbed on Co sites. This supports that new Co sites are formed over CoH-FBZ.6 SO₂-TPSR results show that stable sulfur compounds are formed over the SO₂ poisoning catalysts. The sulfur compounds occupy part of the active sites, lead to the amount of the active species -NO_y decrease, and the catalytic activity of the catalysts is inhibited. In contrast to that over the catalysts CoH-Beta with single topology structure, the sulfur compounds is less stable over the catalysts CoH-FBZ with composite topology structure. Increasing the reaction temperature, part of the sulfur compounds is desorbed and the active sites are released. As a result, the composite catalyst CoH-FBZ exhibit better SO₂ tolerance than CoH-Beta due to the less stable adsorption of sulfur species over CoH-FBZ than over CoH-Beta, as revealed by SO₂-TPSR results.II) Research progresses of CH₄-SCR in CoH-ZSM-5Combined NO₂, NO （O₂） adsorption and temperature programmed desorption （TPD） have been studied systematically to probe into the selective catalytic reduction of NO by methane （CH₄-SCR） over CoH-ZSM-5 （SiO₂/Al₂O₃=25）. Selective catalytic reduction of NO or NO₂ by CH₄ over CoH-ZSM-5 are also investigated.1 Catalytic activity results show that in the absence of oxygen, low NO to N₂ conversion is obtained. Addition of oxygen, the catalytic activity increases significantly. In the reaction system of NO/CH₄/O₂ and NO₂/CH₄/O₂, same NO or NO₂ to N₂ conversion is obtained, the CH₄ conversion is also comparable. In the absence of oxygen, same NO₂ to N₂ conversion is obtained in the NO₂/CH₄ reaction as that in the presence of oxygen at temperature lower than 673 K. Further increasing the reaction temperature, catalytic activity decreases.2 Adsorption conditions significantly affect the adsorption of NO, NO₂ and NO+O₂. Adsorbed NO species are unstable and desorbed below the reactive temperature 523 K. Increasing adsorption temperature results in the decrease of the adsorbed NO species amount.3 The amount of-NO_y species formed from NO₂ adsorption increases with the increase of NO₂ concentration in the adsorption process, while decreases significantly with the increase of adsorption temperature. Though NO species are adsorbed weakly on CoH-ZSM-5, competitive adsorption between NO and -NO_y species decreases the amount of adsorbed -NO_y species. Similar desorption profiles of NO₂ was obtained over CoH-ZSM-5 while it was contacted with NO₂ or NO+O₂ followed by TPD. If NO₂ was essential to form adsorbed -NO_y species, the amount of adsorbed -NO_y species for NO+O₂ adsorption should be the least among the adsorption of NO₂, NO+O₂ and NO+NO₂ because of the lowest NO₂ concentration and highest NO concentration. In fact, the amount of adsorbed -NO_y species is between the other two adsorption processes. These indicate that formation of adsorbed -NO_y species may not originate from NO₂.4 O₂ promotes the CH₄-SCR activity by reacting with adsorbed NO or NO₂ to form sufficient amount of active -NO_y species.更多还原