【作者】 姚杰；

【导师】 郑锺植； 马放；

【作者基本信息】 哈尔滨工业大学 ， 环境科学与工程， 2009， 博士

【摘要】 为降解挥发性有机物,并解决挥发性有机物带来的环境问题,分别以γ-Al₂O₃、SiO₂为载体,以V₂O₅、TiO₂、V₂O₅-TiO₂作为活性成分,采用溶胶-凝胶法负载TiO₂和浸渍法负载V₂O₅,制备出了负载型催化剂。同时,以甲苯的催化氧化为模型反应,建立了动态催化氧化反应体系。利用该反应体系研究了催化剂的催化活性,以及影响催化性能的因素。通过对不同载体不同活性组分催化剂的活性测试,可以得出V₂O₅-TiO₂/SiO₂对甲苯的降解能力最强。同时,对载体粒径、不同前驱物及催化剂负载量与催化剂性能的关系进行了测试和分析,得出γ-Al₂O₃最佳载体粒径为60～80目;采用偏钒酸铵的乙二酸溶液作为前驱物制备的催化剂效果最好;V₂O₅的最佳负载量为1wt.%,V/Ti比值为0.127。对催化反应中的三个主要因素:反应温度、进气流量、进气浓度进行了研究。实验结果表明V₂O₅-TiO₂/SiO₂催化剂具有较低的起燃温度,而且它对甲苯的去除率随温度的升高迅速上升,和贵金属的催化特性相似;进气流量及浓度的增加,并没有使V₂O₅-TiO₂/SiO₂催化剂对甲苯的去除效果发生太大的变化;相反却导致V₂O₅-TiO₂/Al₂O₃催化剂对甲苯去除率的降低。与V₂O₅-TiO₂/Al₂O₃相比,V₂O₅-TiO₂/SiO₂具有较强的抗冲击能力。采用XRD、SEM、EDX、XPS对制备的催化剂的体相结构和表面特性进行了表征。结合表征和活性测试的结果,分析了催化剂结构与催化性能之间的关系。结果发现较少的V₂O₅负载量使得V离子嵌入了TiO₂的晶体结构中,而不是形成晶形V₂O₅,并形成了V-O-Ti键;TiO₂与SiO₂发生了化学反应,有Ti-O-Si键形成,而对于Al₂O₃载体来说,TiO₂和它之间只是简单的物理结合。由活性测试的结果可看出,这些化学键有可能是催化剂的活性位,它们的生成有利于提高催化剂的催化性能,有利于增加催化剂各组分间的结合力,增强催化剂的强度。分别以γ-Al₂O₃、SiO₂为载体,CuO为活性组分,添加Ce,用浸渍法制备了负载型催化剂。同时,以甲苯的催化氧化为模型反应,建立了动态催化氧化反应体系。利用该反应体系研究了催化剂的催化活性,以及影响催化性能的因素。在以不同载体制备的各种催化剂中,以60～80目的γ-Al₂O₃作载体的催化剂对甲苯的去除效果最好。相对于CuO/Al₂O₃催化剂,添加Ce后的CuO-CeO₂/Al₂O₃催化剂对甲苯催化氧化的起燃温度和完全转化温度均有明显的降低。研究表明,当以60～80目的γ-Al₂O₃作载体,Cu的负载量为5wt.%,Cu与Ce的比为1:1,催化剂的焙烧温度为500℃,焙烧时间为6小时的CuO-CeO₂/Al₂O₃催化剂的催化活性最高。针对甲苯和二甲苯催化反应中的三个主要因素（反应温度、空速、进气浓度）进行了研究。在测试范围内,CuO-CeO₂/Al₂O₃对甲苯的最佳空速为8000h-1,对CuO/Al₂O₃为6000h-1。以二甲苯为目标物的催化性能影响因素实验所得结果与甲苯的相似,CuO-CeO₂/Al₂O₃和CuO/Al₂O₃的最佳空速均为8000 h-1。和催化氧化甲苯的实验相比,CuO/Al₂O₃催化剂对二甲苯的处理效果相对较好,在不同的空速和进气浓度下去除率都在90%以上,虽然能够达到二甲苯去除要求,但与CuO-CeO₂/Al₂O₃相比仍不能达到最佳的处理效果。CuO-CeO₂/Al₂O₃催化剂具有较强的抗冲击能力,能够更好的适用于实际应用中。采用XRD、SEM、EDX、XPS对所制备的催化剂进行了表征。结果表明,添加了铈后的CuO-CeO₂/Al₂O₃催化剂表面氧化物颗粒的粒径有所减小,分散也更为均匀。在CuO/Al₂O₃催化剂中添加适量的CeO₂可促进催化剂表面Cu+含量的增加,从而有利于甲苯、二甲苯催化氧化活性的提高。为实现用NH3对NOx的选择性催化还原,研究了一种V₂O₅/TiO₂/Al₂O₃/Al金属丝网蜂窝催化剂。以铝丝网为载体,先对其进行阳极氧化,使其表面变得多孔易于吸附,然后用溶胶凝胶方法负载TiO₂,最后采用浸渍法负载V₂O₅;制成V₂O₅/TiO₂/Al₂O₃/Al筛网蜂窝型催化剂。这种催化剂具有高开孔结构,较高的传质系数和适中的压力降。而且金属筛网良好的延展性,使其具有可变性,适合于各种形状反应器的安装。此外,该催化剂具有机械强度高、抗震性能好、成本低等优点。与此同时,采用60～80目的氧化铝小球为载体,用同样的方法负载同样的组分,制成V₂O₅/TiO₂/Al₂O₃催化剂,用于与筛网蜂窝催化剂做比较。对两种催化剂进行活性考察,结果表明两种催化剂具有较宽的活性温度范围,在200～400℃下得到较好的处理效果,其中筛网蜂窝催化剂的最高NO转化率为86%,粉末催化剂为93.8%;两种催化剂均能在较大的空速范围内有较好的处理效果;对于两者来说提高氨氮比和进料气浓度都可以提高NO的转化率。采用XRD、SEM、EDX、XPS对制备的催化剂进行了表征。结果表明,在TiO₂煅烧的过程中发生了烧结,铝网上的氧化铝与二氧化钛粘结在一起,在筛网蜂窝催化剂上较好地负载了TiO₂;少量的V₂O₅负载到载体上,在载体上并未发现V₂O₅晶型。对两种催化剂进行了反应动力学的初步研究。研究结果认为V₂O₅/TiO₂催化剂进行选择性催化还原NO是按Eley-Rideal机理进行的,为一级反应。筛网蜂窝催化剂在低温下反应主要受化学动力学的控制,高温下反应受传质控制。为探索组合电化学催化和光催化氧化过程降解反应性黑5的可行性,在三种不同的金属丝网电极上研究了染料反应性黑5的电化学催化氧化和光助电化学催化氧化。它们是H₂气氛中,800℃烧结10小时涂钛的金属丝网电极; H₂气氛中,800℃下烧结10小时然后在空气中600℃煅烧3小时的TiO₂/Ti涂层金属丝网电极和纯钛金属丝网电极。试验结果表明以HCl为支持电解质和添加剂,对染料反应性黑5处理20分钟的脱色率:H₂气氛中,800℃烧结10小时涂钛的金属丝网电极和H₂气氛中,800℃下烧结10小时然后在空气中600℃煅烧3小时的TiO₂/Ti涂层金属丝网电极上高达85%。在TiO₂/Ti金属丝网电极上利用紫外辐射研究了染料反应性黑5的光助电化学催化氧化。向电化学反应系统引入紫外辐射会提高染料反应性黑5的脱色效果,尤其在H₂气氛中,800℃下烧结10小时然后在空气中600℃煅烧3小时的TiO₂/Ti涂层金属丝网电极上。恰是空气中煅烧形成的TiO₂在紫外辐射下光催化降解了染料反应性黑5。比较单独使用电化学和光催化降解过程可以肯定存在两种过程的协同作用。更多还原

【Abstract】 In order to decompose volatile organic compounds （VOCs） and solve the problems caused by VOCs to the environment, catalysts for the catalytic oxidation of toluene were prepared by sol-gel and impregnation methods, usingγ-Al₂O₃ or SiO₂ as carriers, V₂O₅, TiO₂ or V₂O₅-TiO₂ as active components. Dynamic catalytic oxidation reaction system was established, from which, the activity of catalysts and reaction conditions were investigated. The results indicated that V₂O₅-TiO₂/SiO₂ illustrates the best ability for the degradation of toluene. The influence of carriers’ size, precursor and loading amount on the activity of catalysts was experimented and analyzed. The best size ofγ-Al₂O₃ was 60-80 mesh; the best precursor was ammonium vanadate in an oxalic acid solution; the best loading amount of V₂O₅ was 1wt. %; and the molar ratio of nV/nTi was 0.127 in terms of treatment efficiency and costs.Three main factors in catalytic oxidation reaction: reacting temperature, space velocity, inlet concentration were investigated. The experimental results indicated that V₂O₅-TiO₂/SiO₂ had low ignition temperature, and efficiency of toluene conversion rose quickly as temperature increases, proving that V₂O₅-TiO₂/SiO₂ possess similar temperature characteristics to noble metal. When space velocity and concentration were changed, efficiency of toluene conversion on V₂O₅-TiO₂/SiO₂ did not change too much. By contrast, efficiency of toluene conversion on V₂O₅-TiO₂/Al₂O₃ descended as space velocity and concentration increased. Compared with V₂O₅-TiO₂/Al₂O₃, V₂O₅-TiO₂/SiO₂ shows better resistance against impact.The prepared catalysts were characterized on structure and morphology by X-ray diffraction （XRD）, Scan Electron Microscope （SEM）, energy dispersion X-ray energy spectrum （EDX） and X-ray photoelectron energy spectrum （XPS）. According to the result of activity test and characterization, the relationship between catalyst structure and catalytic activity was analyzed. The results showed that vanadium ion was imbedded in the crystal structure of TiO₂, instead of creating V₂O₅ crystal form because of limited V₂O₅ loaded amount. The chemical bonds of V-O-Ti and Ti-O-Si were formed. However, there was only physical combination betweenγ-Al₂O₃ and TiO₂. The result of activity test indicated that these chemical bonds might be the active sites of catalysts which increase the catalytic capability of catalysts and strengthen the binding strength among the components of catalysts.The CuO-CeO₂/Al₂O₃ catalysts were prepared by impregnation methods, usingγ-Al₂O₃ or SiO₂ as carriers, CuO as active component, and with addition of Ce. Using the catalytic oxidation of toluene and xylene as the model reaction, dynamic catalytic oxidation reaction system was established from which the activity of catalysts and reaction conditions were investigated. In all kinds of catalysts using different carriers, the one usingγ-Al₂O₃ （60～80mesh） as carrier had the best ability on the degradation of toluene. Compared with CuO/Al₂O₃ catalyst, CuO-CeO₂/Al₂O₃ catalyst which was added with Ce had lower initial combustion temperature and complete oxidation. The prepared process was optimized and the results showed that the catalyst with 5 wt.% Cu loading amount, molar ratio of Cu/Ce 1:1 and calcined at 500℃for 6 hours has the highest catalytic activity.Three main factors such as reacting temperature, space velocity, inlet concentration in the catalytic oxidation reaction were researched for toluene and xylene degradation. In test range, the optimal space velocity of toluene on CuO-CeO₂/Al₂O₃ was 8000h-1, and 6000h-1 for CuO/Al₂O₃. The results of influencing factors experiment on catalytic capability of xylene were similar to that of toluene, and the optimal space velocity of xylene on CuO-CeO₂/Al₂O₃ and CuO/Al₂O₃ was 8000h-1. Compared with the catalytic oxidation of toluene, the xylene removal efficiency on CuO/Al₂O₃ was preferable, and it was over 90% in different space velocity and inlet concentration. The removal purpose of xylene could be achieved but it was not preferable compared to CuO-CeO₂/Al₂O₃. CuO-CeO₂/Al₂O₃ has better resistance against impact and can be better applied in the practice.The prepared catalysts were characterized by XRD, SEM, EDX and XPS. The results indicated that surface particle diameter of CuO-CeO₂/Al₂O₃ catalyst became smaller when Ce added, and the dispersion was well proportioned. The presence of CeO₂ increased the Cu+ content on the surface of CuO/Al₂O₃ catalysts. So the activity of catalysts for toluene and xylene catalytic oxidation could be improved. To realize the selective catalytic reduction （SCR） of NOx with NH3, a new type of V₂O₅/TiO₂/Al₂O₃/Al wire-mesh honeycomb （WMH） catalyst was developed. The wire-mesh honeycomb made of aluminum was first oxidized as anode electrochemically to form porous layer, and then TiO₂ was adsorbed by sol-gel method, and V₂O₅/TiO₂ catalyst powder was wash-coated onto the wire surface of the honeycomb. V₂O₅/TiO₂/Al₂O₃/Al/WMH catalyst was applied for SCR of NOx with NH3. The catalyst shown high mass transfer coefficient and moderate pressure drop because of its porous structure. Wire-mesh has high extendibility and flexibility, and is suitable to reactors with different structures.The selective catalytic reduction activity of two types of catalysts, V₂O₅/TiO₂/Al₂O₃/Al WMH catalyst and powder catalyst, were investigated, and the results showed that they had wide active temperature range and high treatment efficiency within the temperature range of 200⁴00℃, the highest conversion of NO over V₂O₅/TiO₂/Al₂O₃/Al WMH catalyst being up to 86% and over powder catalyst 93.8%. They could both get high treatment efficiency in a wide range of space velocity. Increasing molar ratio nNH3/nNO and concentration of influent gas could enhance NO conversion for both of them. And the treatment effectiveness over powder catalyst was better than that over WMH catalyst, but bed pressure drop of powder catalyst was severely high which would limit its application. The manufactured catalysts were characterized by XRD, SEM, EDX and XPS and the results showed that TiO₂ was well combined with Al₂O₃ and V₂O₅ was fully dispersed. Reaction kinetics of two types of catalysts was primarily studied, and the results indicated that SCR of NOx with NH3 over V₂O₅/TiO₂ catalyst accorded with Eley-Rideal mechanism and belonged to first order reaction. Reaction over WMH catalyst was mainly controlled by chemical kinetics at low temperature and was affected by mass transfer characteristics at high temperature. For powder catalyst with 60⁸0 meshes, the reaction was controlled by reaction kinetics and not by mass transfer.To investigate the feasibility to combine the electrochemically catalytic oxidation process and photo catalytic process to decompose Reactive Black 5, the efficiency of the electrochemically catalytic oxidation process and photo-electric catalytic process for the degradation of Reactive Black 5 were studied on three different wire-mesh electrodes. They are Ti coated wire-mesh electrode sintered at 800℃for 10 hours with H₂; TiO₂/Ti coated wire-mesh electrode sintered at 800℃for 10 hours with H₂ and calcined at 600℃for 3 hours with air and fresh titanium wire-mesh electrode. The experiment result shown that with HCl as supporting electrolyte and additive, the coloring removing efficiency of Reactive Black 5 reach as high as 85% less than 20 minutes at Ti coated wire-mesh electrode sintered at 800℃for 10 hours with H₂ and at TiO₂/Ti coated wire-mesh electrode sintered at 800℃with H₂ for 10 hours and calcined at 600℃for 3 hours with air. Electrochemically promoted photo catalytic degradation of Reactive Black 5 was studied with UV irradiation on TiO₂/Ti wire-mesh electrodes. It is found that the introduction of UV irradiation to the electrochemical system would enhance the color removing efficiency for Reactive Black5 degradation especially on TiO₂/Ti coated wire-mesh sintered at 800℃for 10 hours with H₂ and calcined at 600℃for 3 hours with air. It is the TiO₂ formed after calcined at 600℃for 3 hours with air that photo-catalyzed the degradation decomposition of Reactive Black 5 with UV irradiation. Compared with decolourization efficiency obtained by individual application of electrochemical and photo catalytic oxidation procedures, a significant synergic function from these two processes could be concluded.更多还原