Fe-BEA Zeolite Catalysts for NH3-SCR of NOx

Iron-containing zeolites are known to be promising catalysts for the NH₃-SCR reaction. Here, we will investigate the catalytic activity of iron-based BEA catalysts, which was found to exhibit improved activities compared to previously described iron-containing zeolite catalysts, such as ZSM-5 and ZSM-12. Series of Fe-BEA zeolite catalysts were prepared using a range of different preparation methods. Furthermore, we found that an iron concentration around 3 wt% on BEA showed a small optimum in SCR activity compared to the other iron loadings studied.     

Tuning the NOx conversion of Cu-Fe/ZSM-5 catalyst in NH3-SCR

Cu-Fe/ZSM-5 catalyst prepared by subsequent ion-exchange showed higher NOx conversion compared with Fe/ZSM-5 or Cu/ZSM-5. Presence of small amount of copper in xCu-yFe/ZSM-5 catalysts was found to be enough to improve the low temperature NOx conversion without significantly affecting the high temperature performance. Co-presence of Cu increases the reducibility of Fe and also increased strong acid sites in Cu-Fe/ZSM-5. However, no correlation between acid site strength and NOx conversion is observed. Higher NOx conversion over Cu-Fe/ZSM-5 can be correlated to the facile reduction of metal species. Thus the redox properties and NOx conversion can be tuned by changing the composition of Cu-Fe/ZSM-5 catalyst.     

Selective catalytic reduction of NOx by NH3 over MoO3-promoted CeO2/TiO2 catalyst

The addition of MoO₃ enhanced the activity of CeO₂/TiO₂ catalyst for the selective reduction of NO_x with NH₃. The MoO₃-promoted CeO₂/TiO₂ exhibited higher activity than CeO₂/TiO₂ even in the co-presence of H₂O and SO₂. This is because the introduction of Mo to the Ce10Ti catalyst can inhibit the adsorption of H₂O and SO₂ as well as the formation of sulfate species on the catalyst surface, thus alleviating the poisoning effect of H₂O and SO₂.     

Porous washcoat structure in CeO2 modified Cu-SSZ-13 monolith catalyst for NH3-SCR with improved catalytic performance

A series of CeO₂ modified Cu-SSZ-13 monolith catalysts were prepared by embedding CeO₂ into the washcoat of Cu-SSZ-13 monolith catalyst through solvent combustion method. These CexCu-SSZ-13 catalysts were studied in the selective catalytic reduction (SCR) of NO with NH₃, among which the Ce2Cu-SSZ-13 catalyst exhibited the best low-temperature activity, hydrothermal stability, and sulfur resistance. The physicochemical properties of the catalysts were characterized using multiple methods. Results showed that the acidity, redox capacity, and ammonia adsorption capacity significantly enhanced after CeO₂ modification, thus leading to the high performance of Ce2Cu-SSZ-13 catalyst. Furthermore, the introduction of CeO₂ induced the fast SCR reaction by promoting the oxidation of NO to NO₂. Analog calculation suggested that the porous structure generated via solvent combustion in the washcoat effectively increased the diffusion rate of reaction. In situ diffuse reflectance infrared Fourier transform spectroscopy (in situ DRIFT) analysis showed that Brønsted acid sites were the main active center and the reaction followed Eley–Rideal mechanism.     

An environmentally friendly FeTiSOx catalyst with a broad operation-temperature window for the NH3-SCR of NOx

A novel FeTiSO_x catalyst prepared by a simple hydrolysis coprecipitation method was used for the selective catalytic reduction (SCR) of NO_x with NH₃, which exhibited high catalytic activity (NO_x conversion of >97% and N₂ selectivity of >95%) and tolerance for both H₂O and SO₂ at a broad temperature window of ~325–475°C. The characterization results showed that the formation of Fe–O–Ti and Fe–O–S species could significantly enhance the acidic sites of the catalyst, which play an important role in NH₃ absorption and their catalytic activity. The Fe³⁺ ions in the bulk anatase TiO₂ could significantly enhance the redox properties for the SCR reaction and suppress the side reaction of NH₃ oxidation to NO or N₂O. In addition, the reaction mechanism was discussed based on in situ diffuse reflectance infrared Fourier transform spectroscopy measurements and kinetic investigation, indicating that the reaction was dominated by the Eley–Rideal mechanism over the FeTiSO_x catalyst.     

Promotion effect and mechanism of MnOx doped CeO2 nano-catalyst for NH3-SCR

MnO_x-CeO₂ (denoted as Mn–Ce) nanorod and MnO_x-CeO₂ nanooctahedra catalysts were synthesized by the hydrothermal method and were used for selective catalytic reduction of NO with NH₃. The catalytic performance tests showed that the NO removal efficiency of CeO₂ catalysts was obviously improved after loading MnO_x. The structure and properties of catalysts had been characterized by SEM、TEM、XRD、BET、XPS、H₂-TPR、NH₃-TPD and in situ DRIFTS. It was found that Mn–Ce catalyst were of uniform core-shell structure, higher concentrations of Mn⁴⁺ and Ce³⁺, better reducibility, the increase of weak acid sites. The results of in situ DRIFTS indicated that the NH₃-SCR reaction should obey the E–R mechanism. Moreover, the promotion effect and mechanism of MnO_x doped CeO₂ was demonstrated, which improved the catalytic activity of Mn–Ce catalysts.     

不同的WO3掺杂量对CeO2的NH3-SCR催化性能影响研究

针对二氧化铈(CeO2)活性低、活性温度范围窄的问题,提出了利用浸渍法合成不同三氧化钨(WO3)掺杂量的CeO2催化剂的方法,发现4％WO3/CeO2(催化剂中W物质的量为Ce物质的量的4％)为最佳WO3掺杂量的铈基催化剂.结果表明,该催化剂在150～425℃的宽温度区间表现出了 90％以上的NOx转化率和N2选择性,...     

MnOx/WO3/TiO2低温选择性催化还原NOx机理的原位红外研究

浸渍法制备15% MnO_x/5% WO₃/TiO₂低温脱硝催化剂,利用原位傅里叶变换红外（in situ FT-IR）设计包括多种吸附反应以及不同预处理方式的微观暂态试验与微观稳态试验,研究其NH₃-SCR脱硝反应机理,并推测反应路径。结果表明,催化剂的NH₃-SCR反应主要以Eley-Rideal机理方式进行,仅在一定温度条件下可以看到Langmuir-Hinshclwood反应路径。催化剂表面Lewis酸位的NH₃吸附是还原剂的主要来源,Brønsted酸位吸附的NH₄⁺随温度上升参与反应的比例略有提高。NH₃的吸附活化是整个反应的控制步骤,吸附态NH₃更易与NO₂发生反应,NO与催化剂表面的相互作用明显弱于NO₂。NO会在催化剂表面氧化活性中心形成大量双齿配位型硝酸盐,阻碍NH₃的吸附和活化,O₂存在条件下促进NH₃-SCR反应进行,阻止NO在催化剂表面形成双齿硝酸盐。NO与NH₃在催化剂表面存在吸附竞争,NO的吸附作用强于NH₃,温度达到100℃后吸附的NH₃方可大量活化并与NO_x发生进一步反应。     

V2O5-WO3-MoO3/TiO2催化剂在柴油机NH3-SCR系统中的性能

针对柴油机运行工况特点及柴油机尾气成分特点,以工业纯锐钛型二氧化钛、偏钒酸铵、偏钨酸铵、钼酸铵为主要原料制备了颗粒状V₂O₅-WO₃-MoO₃/TiO₂催化剂,以Lister Petter TR1重型直喷式单缸柴油机为依托搭建试验台,研究了在真实柴油机尾气环境下催化剂的脱硝性能。结果表明,柴油机负载增大,催化剂脱硝活性呈现下降趋势。1800 r·min^-1时,脱硝活性最大值87.1%在负载25%、反应温度380℃、空速20000 h^-1、氨氮比1.0处取得。柴油机负载不同,导致催化剂活性温度窗口(脱硝活性>70%)发生较大变化,与负载25%相比,负载50%活性温度窗口减小约60℃。增大柴油机负载可以提高NH₃/N₂O反应起始温度,但是同时会导致高温区间(>400℃)N₂O生成量增大。     

过渡金属型锰基低温NH3-SCR脱硝催化剂研究综述

综述了一元至多元过渡金属与锰的复合氧化物和负载型过渡金属与锰基催化剂的低温脱硝性能,着重阐述了在不同活性组分下,制备出不同结构的过渡金属催化剂对脱硝活性的影响。分析总结了过渡金属催化剂在低温NH₃-SCR中的反应机理及其抗水抗硫性能,最后,针对过渡金属催化剂存在的问题,展望了该领域未来可能的发展方向和研究热点。     

SO2对稀土精矿催化剂NH3-SCR脱硝催化性能的影响

抗硫性能是评价脱硝过程中催化剂性能的关键指标,研究SO₂对催化剂理化特性的影响对催化剂脱硝应用具有重要意义。通过焙烧处理白云鄂博稀土精矿得到稀土精矿催化剂,利用催化剂抗硫性能实验台,结合SEM、BET、XRD和FT-IR,分析了O₂、NH₃、NO气氛下SO₂在催化剂表面的吸附及不同SO₂浓度对催化剂催化脱硝性能的影响。结果表明, SO₂对稀土精矿催化剂脱硝性能有显著的促进作用,300℃时,NO转化率从28%提高至50%,350℃时,NO转化率从42%提高至75%; SEM、BET和XRD结果表明催化剂抗硫性能测试前后的物理结构和化学组成基本保持不变,稀土精矿催化剂具有较好的抗硫性能;FT-IR结果证实SO₂的吸附使稀土精矿催化剂表面B酸性位点增多,催化剂对NH₃的吸附能力增强,因此有利于提高催化剂活性。研究结果可为白云鄂博稀土精矿催化剂NH₃-SCR脱硝应用过程中抗硫性能提供有价值的基础数据参考。     

双金属交换的Cu-Mn/SSZ-39催化剂的NH3-SCR脱硝性能

摘要：以SSZ-39为载体,采用离子交换法制备不同铜锰物质的量比的Cu-Mn/SSZ-39分子筛催化剂,并考察其在以NH3为还原剂的选择性催化还原NO反应（NH3-SCR）中的脱硝活性。通过XRD、SEM、N2吸脱附、NH3-TPD、H2-TPR、XPS、ICP等对催化剂的结构、形貌、表面酸性等进行表征。结果表明,Cu2 提供主要的反应活性位,使催化剂具有良好脱硝活性和N2选择性;Mn2 /3 交换提 高了催化剂的表面酸性,特别是增加了弱Lewis酸的含量;Cu2 、Mn2 /3 双金属交换的Cu-Mn/SSZ-39催化剂具有良好的低温脱硝活性和水热稳定性。当Cu与Mn的物质的量比为1:0.6时,Cu-Mn(0.6)/SSZ-39具有最低的起燃温度（T50为125 ℃）,在184~433 ℃的宽温度范围内转化率达到90%以上,并在450 ℃内保持90%以上的N2选择性。水热老化后的Cu-Mn/SSZ-39-A基本保持了原有的晶型、形貌和脱硝活性,体现了良好的水热稳定性。     

稀土掺杂铁锰脱硝催化剂的制备及其性能研究

实验采用共沉淀法制备铈掺杂铁锰氧化物脱硝催化剂,对催化剂进行了XRD,TPR和比表面积表征和测试,并时不同铈含量的催化剂进行脱硝性能研究.结果表明,催化剂中添加氧化铈后无规则和非晶态粒子增多,催化剂的低温还原能力有所增强.当稀土氧化物添加量在1％～10％之间时,比表面积呈现递增趋势,添加6％氧化铈的催化剂孔容最大.脱硝实验表明,铈含量增大提高了催化剂在低温区脱硝活性.在500℃以后,随温度的继续增高,催化剂的NOx脱除率开始降低.     

改性催化剂织构强化低温NH3-SCR脱硝性能的研究进展

采用选择催化还原技术（SCR）有效脱除NO_x的关键在于高效催化剂,而催化剂脱硝性能主要取决于催化剂的物理化学性质,催化剂织构特性的差异对于催化剂低温活性及抗中毒性能具有重要的影响。本文综述了近年来通过改性催化剂织构强化催化剂脱硝性能的研究进展,重点阐述了通过拓展催化剂载体比表面积及提高活性物质的表面分散性等织构改性来优化催化剂微观形态,由此提高催化剂低温脱硝性能;同时介绍了改性催化剂织构的常用方法;并总结了近年来国内外学者对特殊结构催化剂的研究,众多文献表明催化剂的特殊结构和形态可以显著改善催化剂的酸性和活性位性质,提高催化剂的脱硝性能和抗中毒性能。在此基础上展望了未来催化剂织构改性的研究方向;寻求更合适的物理化学方法应用到催化剂织构改性、进一步采用仿真模拟技术用于催化剂研究以及继续开发研究特殊结构催化剂并应用到工程实践中。     

双金属交换的Cu-Mn/SSZ-39催化剂的NH3-SCR脱硝性能

以SSZ-39为载体,采用离子交换法制备不同铜锰物质的量比的Cu-Mn/SSZ-39分子筛催化剂,并考察其在以NH3为还原剂的选择性催化还原NO反应(NH3-SCR)中的脱硝活性.通过XRD、SEM、N2吸脱附、NH3-TPD、H2-TPR、XPS、ICP等对催化剂的结构、形貌、表面酸性等进行表征.结果表明,Cu2+提...     

Changes in the chemical composition of V2O5-loaded CVC-TiO2 materials with calcination temperatures for NH3-SCR of NOx

In this study, the aim was to evaluate the effect of calcinations temperature on the catalytic activity and chemical composition of V₂O₅/TiO₂. We prepared V₂O₅-loaded CVC-TiO₂ catalysts by a combination of chemical vapor condensation (CVC) and impregnation method at different calcination temperatures. These catalysts were analyzed for their ability to catalyze NH₃-based selective catalytic reduction of NO_x. Compared with V₂O₅ loaded P25-TiO₂ (commercial). V₂O₅/CVC-TiO₂ catalysts calcined above 200 °C exhibited better performance towards NO_x conversion than that by a commercial catalyst prepared using P25-TiO₂ (calcined at 500 °C). In addition, the NO_x conversion rate obtained with the sample calcined at 500 °C gave the best result (90 %) at a reaction temperature of 200 °C. From the XPS results, we observed that the V^4+/5+ ratio was well balanced when the V₂O₅ loaded CVC-TiO₂ sample was calcined at 500 ºC.     

Regeneration of SO2-poisoned diesel oxidation Pd/CeO2 catalyst

Ce(SO₄)₂ is formed on SO₂ poisoned Pd/CeO₂ catalyst, inducing a decrease in catalytic activity. And the activity just partially recovers after regeneration although Ce(SO₄)₂ is eliminated. The BET surface area decreases severely and the size of both Pd and CeO₂ crystallites increases after regeneration. This is due to the decrease of PdO–CeO₂ interaction by Ce(SO₄)₂ on sulfated samples and the hydrothermal effect of regeneration process.     

MnOx-CeO2 shell-in-shell microspheres for NH3-SCR de-NOx at low temperature

A novel MnO_x-CeO₂ catalyst with shell-in-shell microsphere structure was successfully prepared by a one-step hydrothermal method for the first time. The obtained catalyst was characterized by SEM, TEM, XRD, N₂ adsorption and desorption, XPS, H₂-TPR and NH₃-TPD in detail, and its catalytic activity was investigated by selective catalytic reduction of NO_x with NH₃. The results showed that the MnO_x-CeO₂ microsphere catalyst presented high catalytic activity at low temperatures (lower than 210 °C), which was much superior to the counterpart MnO_x-CeO₂ catalyst without shell-in-shell microsphere structure prepared by co-precipitation method.