SO2对MnOx/PG催化剂低温脱硝的影响机理研究

采用等体积浸渍法制备了锰氧化物负载凹凸棒石(MnO_x/PG)低温SCR催化剂,通过SO₂暂态响应、程序升温表面反应(TPSR)等实验技术研究了烟气中SO₂对催化剂SCR脱硝活性的影响行为.采用程序升温脱附(TPD)、BET比表面及孔径分布测定、XPS等表征技术对催化剂硫中毒的机理及化学本质进行了深入分析.结果表明,低温下烟气中SO₂对MnO_x/PG催化剂的SCR脱硝活性存在显著的抑制作用,催化剂中毒主要由烟气中SO₂的催化氧化引起.一方面SO₂氧化为SO₃后与NH₃及H₂O竞争反应形成复杂的硫酸铵盐堵塞催化剂孔道,另一方面与活性组分MnO₂结合形成MnSO₄使得部分活性组分形态发生变迁.其中硫酸铵盐的形成可通过适当的热处理得以去除,而MnSO₄则不可恢复,但催化剂SCR活性却显著增加,表明MnSO₄的形成不是催化剂失活的主要因素.吸附态的硫可显著增加催化剂表面酸性,因此对SCR活性有促进作用.催化剂失活主要机理为:由气相SO₂的连续氧化并与NH₃相结合形成硫酸铵盐,并且在低温下难以分解,以致堵塞催化剂活性中心.     

煅烧菱铁矿制备纳米结构化α-Fe2O3及其NH3-SCR脱硝活性研究

利用菱铁矿的热分解特性,在空气中不同温度下(400、500、600、700、800℃)煅烧天然菱铁矿制备具有纳米尺寸形貌特征的α-Fe_2O_3,作为NH_3选择性催化还原(NH_3-SCR)脱硝的催化剂.采用X射线衍射(XRD)、程序升温脱附(NH_3-TPD)、X射线光电子能谱(XPS)、紫外-可见漫反射吸收光谱(UV-Vis DRS)等手段对催化剂结构进行表征,并利用气固相催化反应系统对催化剂的NH_3-SCR脱硝活性和N_2选择性进行评价,同时考察其抗水抗硫及稳定性.结果表明,天然菱铁矿于空气中500℃煅烧相变为α-Fe_2O_3,具有最低的晶体尺寸(约10 nm)、最高的比表面积(39.68 m~2·g~(-1))和最优的脱硝活性;500℃煅烧菱铁矿制备的催化剂在250~400℃温度窗口内脱硝效率达到100%,并能保持较高的N_2选择性,这主要归因于其具有的纳米多孔结构特性和较大的比表面积,以及表面丰富的酸性位点和吸附态氧.当同时存在5%H_2O和0.04%SO_2时,α-Fe_2O_3在250~400℃区间的脱硝效率高于88%,且在300℃下持续反应360 min,脱硝效率维持在75%以上,表明500℃煅烧菱铁矿制备的催化剂具有良好的抗水抗硫和稳定性.     

TiO_2对In-Ag-O/γ-Al_2O_3催化剂上CO选择性还原NO的改性研究

以Ti O2、γ-Al2O3及Ti O2-γ-Al2O3复合氧化物为载体,以In-Ag-O基为活性组分,采用等体积浸渍法制备了一系列In/Ag催化剂,通过XRD、BET、SEM、H2-TPR等技术手段对催化剂表面形态进行分析,并考察了催化剂对CO选择性还原NO的反应活性和载体中Ti O2含量对催化性能的影响.结果表明,Ti O2的添加促进了活性组分铟和银物种的分散,当Ti O2的含量为载体的15%时制备的催化剂活性最高,合适的Ti O2与γ-Al2O3配比使活性组分与载体之间发生了强烈的相互作用,由此提高了CO选择性还原NO的活性.     

Cu-Al2O3中骨架铜类芬顿催化去除水中有机污染物

为解决传统铁基芬顿催化剂在水体通常酸碱(pH6)条件下活性低的问题,采用简单共沉淀法制备了Cu掺杂的Al_2O_3类芬顿催化剂.通过X射线衍射(XRD)、X射线光电子能谱(XPS)和紫外可见(UV-vis)吸收光谱分析表明,Cu-Al_2O_3中铜掺杂的质量分数低于4.77%时,催化剂中铜主要以Cu~(2+)和Cu~+的形式共存于Al_2O_3的骨架结构中,形成Al—O—Cu键;过量的铜掺杂会导致外骨架铜物种如铜氧化物团簇的存在.以难降解有机污染物2-氯苯酚(2-chlorophenol,2-CP)和染料罗丹明B(Rhodamine B,Rh B)为目标污染物,对Cu-Al_2O_3的类芬顿催化性能进行了详细地研究.结果表明,骨架铜物种在中性温和条件下对2-CP和Rh B显示出很高的催化去除效率和稳定性,反应2 h,Cu-Al_2O_3(Cu质量分数4.77%)对2-CP的去除率达到54%,相应的TOC去除率达到49%,而铜离子溶出浓度仅为0.025 5 mg·L-1,而Cu-Al_2O_3(Cu质量分数7.58%)由于外骨架铜的存在导致催化活性增加缓慢和稳定性下降.ESR测试结果表明,·OH和HO_2~-/O_2~-·是反应中主要的活性物种.     

Ce-Zr-Ox/ATS复合催化剂的制备及其催化氧化Hg0性能研究

采用等体积浸渍法制备了一系列的Ce-Zr-O_x/ATS复合催化剂,在模拟燃煤烟气中研究Ce-Zr-O_x/ATS复合催化剂催化氧化单质汞(Hg~0)的活性.结果表明,当空速小于7000 h~(-1)时,催化剂在200~350℃的温度区间内催化氧化活性能达到80%以上.当空速为3000 h~(-1),HCl浓度为20 mg·m~(-3),氧含量为6%(体积分数),350℃时催化剂活性最高为94.70%.催化剂表征结果表明,催化剂比表面积、孔容和孔径与汞脱除能力没有相关性.抗硫实验表明,SO_2会抑制Hg~0的脱除反应,原因是SO_2与HCl在催化剂表面活性位上的竞争吸附.300℃时,通入NH_3对催化活性有一定的抑制作用,原因是NH_3会与Hg~0和HCl在催化剂表面产生竞争吸附.     

La0.8Ca0.2FeO3/MgAl2O4丝网整体催化剂用于低浓度甲烷催化燃烧

开发了涂覆在金属丝网基体上的La_(0.8)Ca_(0.2)FeO_3/MgAl_2O_4复合整体催化剂,用于低浓度甲烷(0.5%,体积分数)催化燃烧反应.首先用沉积-沉淀法制备了La_(0.8)Ca_(0.2)FO_3(LCF)钙钛矿与Mg Al_2O_4尖晶石复合的粉末催化剂LCF/Mg Al2O4,用程序升温微反应器(TPRS)测定了粉末活性,结合XRD、BET、SEM、TPR的表征结果,筛选出了最佳复合物质的量比和最适焙烧温度.当LCF与Mg Al_2O_4复合后,抗烧结能力增强,以拟一级反应速率常数(k,L·g~(-1)·s~(-1))计的活性提高了1倍左右.然后采用浆料涂覆法,在表面改性的金属丝网蜂窝基体上分层涂覆了作为第二载体的MgAl_2O_4和LCF/Mg Al_2O_4复合粉体涂层,考察了复合粉体球磨前焙烧的温度、第二载体及活性层涂覆量的影响.最后在空速GHSV=40000 h~(-1)条件下测试了甲烷催化燃烧反应的活性.与陶瓷基体相比,涂覆在金属丝网基体上的LCF/MgAl_2O_4活性在600℃时提升了48.1%.500 h长运转试验发现,催化剂活性在初期的200 h下降了20.3%,然后基本保持稳定.     

CuxCe1-xO2/γ-Al2O3催化剂催化燃烧甲苯性能的研究

以γ-Al₂O₃ 为载体,以复合氧化物Cu_xCe_1-xO₂为活性组分,其中,x=0.1,0.2,0.4,0.6,0.8,通过浸渍法制备了一系列Cu_xCe_1-xO₂/γ-Al₂O₃催化剂.在固定床反应器中评价了催化剂对甲苯的催化活性,通过XRD、SEM对催化剂进行表征,并运用ICP-MS分析并计算Cu、Ce的摩尔比以及活性组分的负载量.结果表明,在Cu_xCe_1-xO₂/γ-Al₂O₃催化剂中Cu、Ce摩尔比的实际值与理论值相近,活性组分的负载量在19%以上,而且对甲苯都有较好的低温催化活性,其中当x=0.2时,即Cu_0.2Ce_0.8O₂/γ-Al₂O₃催化剂对甲苯的催化活性最高,其中T₁₀=160 ℃,T₉₀=265 ℃;当甲苯的进口浓度在700~3000 mg·m^-3时,进口浓度对Cu_0.2Ce_0.8O₂/γ-Al₂O₃催化剂的催化活性影响较小,且经过连续80 h的稳定性操作后转化率仍然保持在90%以上.     

ZrO_2晶相对锰铈系SCR催化剂脱硝活性的影响

采用浸渍法制备了以nm级c-Zr O2(立方相Zr O2)、t-Zr O2(四方相Zr O2)和m-Zr O2(单斜相Zr O2)为载体的负载型Mn Ox-Ce O2/Zr O2催化剂,并在连续流动固定床反应器上考察了催化剂的NH3-SCR低温脱硝性能.结果表明,催化剂脱硝性能良好,当Mn Ox负载量(以w计)为15.0%时,以c-Zr O2为载体的催化剂脱硝效率在103℃即可达到100%.在相同活性组分负载量和反应温度条件下,各催化剂的低温脱硝活性体现出Mn Ox-Ce O2/c-Zr O2Mn Ox-Ce O2/t-Zr O2Mn Ox-Ce O2/m-Zr O2的规律,因此对Mn Ox负载量为5.0%的Mn Ox-Ce O2/Zr O2系列催化剂进行进一步表征,以探究该规律的内在影响因素.BET测试结果表明,以c-Zr O2为载体的催化剂的比表面积最大,达到39.67 m2/g,更有利于气体和催化剂表面活性位的接触.XPS测试结果表明,以c-Zr O2为载体的催化剂表面晶格氧含量最丰富,有助于Lewis酸性位的形成.TPR和TPD测试图谱中的峰强及峰面积表明,以c-Zr O2和t-Zr O2为载体的催化剂表面主要存在Lewis酸性位;而在以m-Zr O2为载体的催化剂表面,Lewis酸性位较多,同时还存在少量的Brnsted酸性位.研究显示,Zr O2晶型结构变化引起Mn Ox-Ce O2/Zr O2催化剂的比表面积、表面活性酸性位的不同是产生晶型效应的原因所在;采用Zr O2作为负载型低温SCR催化剂载体时,以立方相晶型结构为最佳.     

聚合物辅助成型法制备纳米Co3O4/CeO2催化剂及其对CO低温氧化性能研究

采用聚合物辅助成型法,以乙二胺四乙酸(EDTA)和聚乙烯亚胺(PEI)为配位体制备了Co_3O_4/CeO_2催化剂,对其进行了氮气吸附、XRD、XPS、SEM、TEM、H2-TPR和CO-TPR等表征,并考察了材料的CO低温催化性能.结果表明,采用聚合物辅助成型法能够合成出具有三维空间网络结构的纳米Co_3O_4/CeO_2催化剂,Ce的加入有利于获得具有更小尺寸的Co_3O_4颗粒,并提高Co3+的相对含量,从而有利于CO低温催化性能的提高;Ce/Co的摩尔比为1时,样品具有最佳的CO催化性能,在催化温度为30℃时,可使初始浓度为100 ppm的CO完全转化;同时,纯氧气加热吹扫有利于催化剂的稳定再生.本研究可为CO低温催化剂的制备提供重要参考.     

富氧条件下等离子体协同改性NaY分子筛催化分解NO_x研究

用不同浓度的Cu、Ce和La离子交换Na Y分子筛,对比了不同改性条件下等离子体协同分解NO_x的性能.实验结果表明:Cu是NO_x催化分解的主要活性组分,对于8%Cu-Na Y催化剂,当放电电压为10 k V,放电功率为7.6 W时,NO_x转化率可达46.3%,反应产物中没有NO_2,只有11 ppm的N_2O.Ce的加入可以有效提高催化剂催化活性,对于5%Ce-8%Cu-NaY催化剂,当放电电压为7.8 kV,功率为3.6 W时,NO_x转化率可达67.3%.La的加入同样可以使催化剂活性上升,但不同La含量催化剂的NO_x转化率相差较小.     

One-pot synthesis of Fe/Cu-SSZ-13 catalyst and its highly efficient performance for the selective catalytic reduction of nitrogen oxide with ammonia

Series of Fe/Cu-SSZ-13 catalysts with different Fe loading content were synthesized by simple one-pot strategy. The obtained catalysts were subjected to selective catalytic reduction (SCR) of NO_x with NH₃ and were characterized by various techniques. The results show that Fe_0.63/Cu_1.50-SSZ-13 catalyst with proper Fe content exhibits excellent catalytic activity with widest operation temperature window from 160 to 580°C, excellent hydrothermal stability as well as good resistance to sulfur poisoning when compared with Cu-SSZ-13, signifying its great potential for practical applications. Further characterizations reveal that the synthesized Fe/Cu-SSZ-13 catalysts present typical chabazite (CHA) structure with good crystallinity, while isolated Cu²⁺ and monomeric Fe³⁺ are revealed as the predominant copper and iron species. At low temperatures, isolated Cu²⁺ species act as primary active sites for SCR reaction, while monomeric Fe³⁺ species provide sufficient active sites for sustain the SCR activity at high temperature. Moreover, Fe over doping would lead to the damage of zeolite structure, destruction of isolated Cu²⁺ site, as well as the formation of highly oxidizing Fe₂O₃, thus causing deterioration of catalytic performances.     

Effect of preparation methods on the performance of CuFe-SSZ-13 catalysts for selective catalytic reduction of NOx with NH3

CuFe-SSZ-13 catalyst showed excellent performance in the selective catalytic reduction of NO_x with NH₃ (NH₃-SCR) for diesel engine exhaust purification. To investigate the effect of preparation methods on NH₃-SCR performance, Fe was loaded into one-pot synthesized Cu-SSZ-13 catalysts through solid-state ion-exchange (SSIE), homogeneous deposition precipitation (HDP) and liquid ion-exchange (IE), respectively. Three CuFe-SSZ-13 catalysts showed similar SO₂ resistance, which was better than that of Cu-SSZ-13. The improvement was attributed to the protection of Fe species. Hydrothermal stability of three CuFe-SSZ-13 catalysts was significantly different, which was attributed to the state of active species caused by different preparation methods. Compared with the other two catalysts, more active species existed inside the zeolite pores of CuFe-SSZ-13_SSIE. During hydrothermal aging, the aggregation of these active species in the pores caused the collapse of catalyst structure, ultimately leading to the deactivation of CuFe-SSZ-13_SSIE. In contrast, Fe species was dispersed better on the surface over CuFe-SSZ-13_IE, enhancing the hydrothermal stability of catalysts. Consequently, Fe loading effectively improved the resistance of SO₂ and H₂O over Cu-SSZ-13. For CuFe-SSZ-13, large amounts of active species located inside the zeolite pores are not beneficial for the hydrothermal stability.     

Activity and hydrothermal stability of CeO2–ZrO2–WO3 for the selective catalytic reduction of NOx with NH3

A series of CeO_2–ZrO_2–WO_3(CZW)catalysts prepared by a hydrothermal synthesis method showed excellent catalytic activity for selective catalytic reduction(SCR)of NO with NH_3 over a wide temperature of 150–550°C.The effect of hydrothermal treatment of CZW catalysts on SCR activity was investigated in the presence of 10% H_2O.The fresh catalyst showed above 90% NO_x conversion at 201–459°C,which is applicable to diesel exhaust NO_x purification(200–440°C).The SCR activity results indicated that hydrothermal aging decreased the SCR activity of CZW at low temperatures(below 300°C),while the activity was notably enhanced at high temperature(above 450°C).The aged CZW catalyst(hydrothermal aging at 700°C for 8 hr)showed almost 80% NO_x conversion at 229–550°C,while the V_2O_5–WO_3/TiO_2 catalyst presented above 80% NO_x conversion at 308–370°C.The effect of structural changes,acidity,and redox properties of CZW on the SCR activity was investigated.The results indicated that the excellent hydrothermal stability of CZW was mainly due to the CeO_2–ZrO_2 solid solution,amorphous WO_3 phase and optimal acidity.In addition,the formation of WO_3 clusters increased in size as the hydrothermal aging temperature increased,resulting in the collapse of structure,which could further affect the acidity and redox properties.     

K2S2O8强化g-C3N4薄膜电极光电催化降解Cu(CN)32-并同步回收Cu

采用高温液相生长法制得g-C_3N_4薄膜电极并作为光阳极,以石墨毡作为阴极,建立了光电催化系统.通过对比光电催化体系、K_2S_2O_8体系以及外加K_2S_2O_8到光电催化体系,发现在光电催化系统下外加K_2S_2O_8可以有效地提高光电催化降解Cu(CN)_3~(2-)的效率,并实现了Cu在阴极上的有效回收.探究了K_2S_2O_8投加量对CN-降解率和Cu回收率的影响,发现当K_2S_2O_8浓度为1 mmol·L~(-1),偏压为1.0 V时,CN-的去除率和Cu回收率分别达到86.23%和82.11%.通过SEM、EDS和XPS分析阴阳极表面形貌,发现部分Cu+被氧化以CuO的形式存在于沉淀和阳极表面,大部分铜离子通过电化学还原作用以单质铜的形式沉积于阴极表面,铜离子有效地从体系中去除.电子顺磁共振及淬灭实验分析表明,CN-的氧化去除是硫酸根自由基(SO·-4)氧化和非自由基氧化共同作用.     

Novel CeO2@TiO2 core–shell nanostructure catalyst for selective catalytic reduction of NOx with NH3

The CeO₂@TiO₂ core–shell nanostructure catalyst prepared by a two-step hydrothermal method was used for selective catalytic reduction (SCR) of NOx with NH₃ in this study. The catalyst presented the obvious core–shell structure, and the shell was amorphous TiO₂ which could protect the active center from the SO₂ erosion. The catalyst showed high activity and stability, excellent N₂ selectivity and superior SO₂ resistance and H₂O tolerance. Characterizations such as TEM, HR-TEM, XRD, BET, XPS, NH₃-TPD, and H₂-TPR were carried out. The results indicated that the catalyst had large surface area and the active sites were well dispersed on the surface. The NH₃-TPD, H₂-TPR and XPS results implied that its increased SCR activity might be due to the enhancement of NH₃ chemisorption and the increase of active oxygen species, both of which were conductive to NH₃ activation. The excellent catalytic performance suggests that it is a promising candidate for SCR catalyst.     

超声辅助法制备新型FeMOR分子筛催化NOx还原反应性能研究

采用超声辅助浸渍法成功合成了高铁含量的Fe MOR-5%-UL催化剂,并且测试其催化还原NO性能.研究发现在超声辅助条件下浸渍制得的催化剂可以引入更高比例的离子交换位上的孤立的Fe~(3+),这些铁离子具有更强的NO还原活性,因此超声辅助浸渍法制备的催化剂催化性能显著高于传统的离子交换法和浸渍法.其中活性最高的FeMOR-5%-UL催化剂在添加SO_2等多种气氛时,催化活性下降不显著.并且在持续100 h的汽车尾气条件下进行的稳定性实验中,FeMOR-5%-UL的催化活性没有明显下降.FeMOR-5%-UL的优异的催化活性和稳定性非常具有应用前景和研究价值.     

Catalytic removal of phenol from gas streams by perovskite-type catalysts

Three perovskite-type catalysts prepared by citric acid method are applied to remove phenol from gas streams with the total flow rate of 300 mL/min, corresponding to a GHSV of10,000/hr. LaMnO_3 catalyst is first prepared and further partially substituted with Sr and Cu to prepare La_(0.8)Sr_(0.2)MnO_3 and La_(0.8)Sr_(0.2)Mn_(0.8)Cu_(0.2)O_3, and catalytic activities and fundamental characteristics of these three catalysts are compared. The results show that phenol removal efficiency achieved with La_(0.8)Sr_(0.2)Mn_(0.8)Cu_(0.2)O_3 reaches 100% with the operating temperature of 200°C and the rate of mineralization at 300°C is up to 100%, while the phenol removal efficiencies achieved with La_(0.8)Sr_(0.2)MnO_3 and LaMnO_3 are up to 100% with the operating temperature of 300°C and 400°C, respectively. X-ray photoelectron spectroscopy(XPS) analysis shows that the addition of Sr and Cu increases the lattice oxygen of La_(0.8)Sr_(0.2)Mn_(0.8)Cu_(0.2)O_3, and further increases mobility or availability of lattice oxygen. The results indicate that La_(0.8)Sr_(0.2)Mn_(0.8)Cu_(0.2)O_3 has the best activity for phenol removal among three catalysts prepared and the catalytic activity of phenol oxidation is enhanced by the introduction of Sr and Cu into LaMnO_3. Apparent activation energy of 48 k J/mol is calculated by Mars–Van Krevelen Model for phenol oxidation with La_(0.8)Sr_(0.2)Mn_(0.8)Cu_(0.2)O_3 as catalyst.     

不同方法制备Co3O4催化剂CO-SCR性能及机制

氮氧化物(NOx)是造成细颗粒物、近地面臭氧等大气污染问题的重要前体物.随着大气污染治理行动的深入,对工业锅炉/窑炉烟气排放的NOx进行控制十分重要.采用不同方法制备了一系列Co_3O_4催化剂,考察了不同制备方法对CO选择性催化还原NO(CO-SCR)反应活性的影响,通过BET、XRD、Raman、HR-TEM和SEM等技术对该系列催化剂进行了表征.活性测试表明,以硫酸钴为前驱体用固态研磨法制备的Co_3O_4-S催化剂具有更优异的CO-SCR反应活性,且表现出较好的抗水蒸气性能,以醋酸钴为前驱体用固态研磨法制备的Co_3O_4-C催化剂显示出较好的抗水性能. NO氧化结果显示,催化剂的NO氧化效果越好,CO-SCR活性也越好. Raman表征结果显示,Co_3O_4-S表面可能含有更多的Co2+离子,从而有利于形成氧空位. H2-TPR结果表明,Co_3O_4-S催化剂的氧化还原性较好. HR-TEM表征发现Co_3O_4-S和Co_3O_4-O主要暴露(111)和(220)晶面,而更多(220)晶面的暴露可能更有利于反应的进行.