Sb modified Fe–Mn/TiO<Subscript>2</Subscript> catalyst for the reduction of NO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> with NH<Subscript>3</Subscript> at low temperatures

Manganese-based catalysts have attracted much attention due to their excellent performance for NO reduction with NH₃ (NH₃-SCR) at low temperatures. In the current study, the novel metal Sb was modified into Mn/TiO₂ and Fe–Mn/TiO₂, and the NO _x conversion was compared with those of Mn/TiO₂ and Fe–Mn/TiO₂ catalysts to investigate the effect of the Sb. The NO _x reduction activities of the catalysts were evaluated in the temperature range of 100–250 °C at a space velocity of 60,000 h^?1. The physicochemical properties of all the catalysts were characterized by Brunauer–Emmett–Teller surface area, temperature-programmed desorption of ammonia, temperature-programmed reduction, X-ray photoelectron spectroscopy, X-ray diffraction, and high-resolution transmission electron microscopy. Interestingly, the Sb-promoted Mn-based catalysts showed significantly higher NO _x conversion than the other catalysts with or without 6 vol% of H₂O. The high performance of the Sb-modified catalysts could be related to the increase of acid sites and redox properties.     

铁基催化剂用于氨选择性催化还原氮氧化物研究进展

氨选择性催化还原NO_x技术可以有效控制氮氧化物的排放。V_2O_5-WO_3(MoO_3)/TiO_2脱硝催化剂虽然已经工业化应用,但其工作温度偏高,不能满足低温宽工作温度窗口等工况的需要。因此,开发具有宽工作温度窗口的低温脱硝催化剂成为研究热点。其中,铁基催化剂因其具有良好的氧化还原性,以及储量丰富、价格低廉、无毒无害等特点,使其在低温氨选择性催化还原(NH_3-SCR)反应中得到了广泛研究。基于Fe_2O_3在NH_3-SCR催化体系中所起的作用不同,从Fe_2O_3作为载体、助剂、活性组分以及新型结构的铁基催化剂等方面系统地介绍了近年来铁基催化剂在NH_3-SCR反应中的最新研究进展。此外,还总结了铁基催化剂的NH_3-SCR反应机理以及抗水抗硫性,并对该领域未来可能的发展方向进行了展望。     

NH3-SCR脱硝催化剂抗硫性能的研究进展

氮氧化物(NO_x)是一种重要的大气污染物, 它造成严重的环境问题, 同时威胁人类健康. 以钢铁烧结烟气为代表的固定源和以柴油机尾气为代表的移动源是氮氧化物的主要来源. 氨气选择性催化还原法(NH₃-SCR)是目前最有效且应用最广泛的NO_x脱除技术. 然而, 无论是固定源还是移动源上NH₃-SCR催化剂, 都不可避免地会被SO₂毒化, 造成催化剂失活, 限制了NH₃-SCR技术的进一步应用. 因此, 研究NH₃-SCR催化剂的SO₂中毒机制以及提高催化剂的抗硫性能至关重要. 我们对固定源脱硝的金属氧化物和移动源上脱硝的Cu基分子筛这两类不同催化剂体系的SO₂中毒机制的研究进展进行了介绍, 并对这两种催化剂上提高抗硫性能改性方法的研究进展进行了评述, 为未来的研究提供了参考.     

Mn-Mo-W-O_x脱硝催化剂活性组分的配伍优化

采用等体积浸渍法制备系列Mn-Mo-W-O_x/堇青石和Mn-Mo-W-O_x/TiO_2催化剂,用于选择性催化还原NO.通过Mn、Mo、W 3种元素不同配比对催化剂配伍进行优化,确立Mn-Mo-W-O_x最佳配比.采用XRD、N_2-BET、PyIR、SEM以及XPS等表征分析催化剂的固相结构、比表面积、酸量、表面形貌和表面元素.结果表明:当Mn/Mo/W元素摩尔比为10∶0.5∶1,载体为TiO_2时,催化剂的催化性能最优.适量Mo掺入Mn-W-O_x催化剂可以增大其比表面积,提高催化剂表面L酸酸量以及Mn~(4+)离子浓度,从而有效提高了催化剂高温活性.载体替换为TiO_2时催化剂的比表面积和酸量明显提高,从而增强了催化剂的脱硝性能.     

Low-temperature selective catalytic reduction of NOx with NH3 over zeolite catalysts: A review

The selective catalytic reduction (SCR) of NO_x by NH₃ is one of the most mature technologies for NO_x treatment. Catalysts are the main factors affecting denitrification efficiency. Zeolites as low-temperature NH₃-SCR catalysts have been extensively studied in the past few years. In this work, the mechanism of zeolites for NH₃-SCR reaction was reviewed and the denitrification performances of zeolite catalysts prepared by different methods were compared. The effects of sulfur and water poisoning on zeolite catalysts in NH₃-SCR reaction were also analyzed. Several ways to address the problems in low-temperature NH₃-SCR reaction were discussed. Hopefully, this review could provide a fundamental understanding of SCR reaction on zeolite catalysts and pave the way toward similar studies to realize its commercial applications.     

氧化铈在氨选择性催化还原氮氧化物中的应用

NH₃选择性催化还原NO_x（NH₃-SCR）是一种广泛应用于以燃煤电厂为代表的固定源和以柴油发动机为代表的移动源NO_x排放控制的技术. 近年来,氧化铈由于具有优异的氧化-还原、储氧和表面酸性等特性而在NH₃-SCR催化剂研究中受到广泛关注. 本文系统综述了氧化铈用作NH₃-SCR催化剂载体、助剂和主催化组分的相关研究,并对该领域未来可能的研究方向进行展望.     

NH3选择性还原NOx技术在重型柴油车尾气净化中的应用

基于实验室对柴油车用V₂O₅-WO₃/TiO₂催化剂配方以及涂覆成型技术的大量研究,设计了一条产量为6000只/月的NH₃选择性催化还原NO_x （NH₃-SCR）催化剂中试生产线,并对生产的催化剂产品进行了发动机台架测试. 结果表明,实验室制备的V₂O₅-WO₃/TiO₂粉体催化剂和生产线产品,在空速为50000 h^-1和200-450 ℃条件下NO_x转化率均可达80%以上;采用大尺寸堇青石载体涂覆后制备的V₂O₅-WO₃/TiO₂整体催化剂经实验室小样测试,在空速为10000-30000 h^-1和250-450 ℃条件下NO_x转化率也为80%以上. 发动机台架测试结果表明,该催化剂产品可使重型柴油机NO_x排放达到国IV标准中欧洲稳态循环（ESC）和欧洲瞬态循环（ETC）排放限值的要求. 该生产线经适当调整后也可用于生产非钒基NH₃-SCR整体催化剂,以满足未来钒基NH₃-SCR催化剂更新换代的需求.     

Solid-phase impregnation promotes Ce doping in TiO2 for boosted denitration of CeO2/TiO2 catalysts

CeO₂/TiO₂（denoted as Ce Ti） catalysts obtained by solid-phase impregnation behaved better in lowtemperature selective catalytic reduction of NO_xwith NH₃（NH₃-SCR） than that by conventional wet impregnation.To explore the main factors for activity distinction,the texture property,CeO₂dispersion and structure changes of TiO₂were comprehensively analyzed.It was found that surface changes of TiO₂had a significant ...     

Shielded Sliding Discharge-Assisted Hydrocarbon Selective Catalytic Reduction of NOx over Ag/Al2O3 Catalysts Using Diesel as a Reductant

The nonthermal plasma generated in a shielded sliding discharge reactor was used to reform diesel for the hydrocarbon-selective catalytic reduction (HC-SCR) of NO_x on Ag/Al₂O₃ catalysts. Compared with raw diesel, the reformed diesel enhanced the NO_x reduction efficiency, mitigated hydrocarbon poisoning of the catalyst and reduced the fuel penalty for the HC-SCR reaction. The NO_x conversion values obtained with a commercial Ag/Al₂O₃ catalyst exceeded that of a 2.0 wt% Ag/Al₂O₃ catalyst prepared by wet impregnation. A significant amount of NH₃ was produced as a by-product during the HC-SCR reaction, which suggests that further NO_x conversion enhancement can be achieved by placing a second NH₃-SCR catalyst in series with the Ag/Al₂O₃ catalyst.     

Co-doping a metal (Cr,Mn, Fe,Co, Ni,Cu, and Zn) on Mn/ZSM-5 catalyst and its effect on the catalytic reduction of nitrogen oxides with ammonia

Selective catalytic reduction (SCR) of NO_x by NH₃ over a series of Mn–M/Z catalysts (M = Cr, Mn, Fe, Co, Ni, Cu, Zn, and Z = the ZSM-5 Zeolite) synthesized by wet impregnation method was investigated. Mn–Fe/Z, Mn–Co/Z, and Mn–Cu/Z catalysts exhibited approximately 100 % NO_x conversion over a wide temperature range (200–360 °C) in a defined atmospheric condition, which was noticeably greater than that of Mn–Cr/Z (340–360 °C). Furthermore, the effect of addition of second metal oxide species to the initial Mn/Z catalyst on the structure of catalysts was studied by several characterization techniques. BET measurements revealed high surface area and pore volume of the Mn–Cu/Z catalyst. In addition, the XRD and UV–Vis DR results showed that addition of co-doped metal oxide species improved the dispersion of metal ions and inhibited crystallization of metal oxides. UV–Vis studies also were in good accordance with DTA/TG results confirming the formation of cobalt oxide and copper oxide clusters in Mn–Co/Z and Mn–Cu/Z catalysts, respectively. The FTIR spectra of pyridine adsorption, in addition, suggested the Mn–Cu/Z catalyst contained the most Lewis acid sites leading to more NO_x adsorption capacity.     

Monolith Manganese-Based Catalyst Supported on ZrO2-TiO2 for NH3-SCR Reaction at Low Temperature

Monolith catalysts were prepared using TiO₂ and ZrO₂-TiO₂ as supports with MnO₂ as active component and Fe₂O₃ as promoter. The catalytic activities at low temperature and stability at high temperature for selective catalytic reduction of NO_x with NH₃ (NH₃-SCR) in the presence of excessive O₂ were studied after the catalysts calcined at different temperatures. The catalysts were characterized by X-ray diffraction (XRD), specific surface area measurements (BET), oxygen storage capacity (OSC), and temperature programmed reduction (H₂-TPR). The results indicated that the catalyst supported on ZrO₂-TiO₂ had excellent stability at high temperature, and possessed high specific surface area and oxygen storage capacity, and had strong redox property. The results of the catalytic activities indicated that the monolith manganese-based catalyst using ZrO₂-TiO₂ as support had evidently improved the activity of NH₃-SCR reduction reaction at low temperature, and it showed great potential for practical application.     

Improving the denitration performance and K-poisoning resistance of the V2O5-WO3/TiO2 catalyst by Ce4+ and Zr4+ co-doping

A series of V₂O₅-WO₃/TiO₂-ZrO₂, V₂O₅-WO₃/TiO₂-CeO₂, and V₂O₅-WO₃/TiO₂-CeO₂-ZrO₂ catalysts were synthesized to improve the selective catalytic reduction (SCR) performance and the K-poisoning resistance of a V₂O₅-WO₃/TiO₂ catalyst. The physicochemical properties were investigated by using XRD, BET, NH₃-TPD, H₂-TPR, and XPS, and the catalytic performance and K-poisoning resistance were evaluated via a NH₃-SCR model reaction. Ce⁴⁺ and Zr⁴⁺ co-doping were found to enhance the conversion of NO_x, and exhibit the best K-poisoning resistance owing to the largest BET-specific surface area, pore volume, and total acid site concentration, as well as the minimal effects on the surface acidity and redox ability from K poisoning. The V₂O₅-WO₃/TiO₂-CeO₂-ZrO₂ catalyst also presents outstanding H₂O + SO₂ tolerance. Finally, the in situ DRIFTS reveals that the NH₃-SCR reaction over the V₂O₅-WO₃/TiO₂-CeO₂-ZrO₂ catalyst follows an L-H mechanism, and that K poisoning does not change the reaction mechanism.     

TiO2负载Mn-Co复合氧化物催化剂上NO催化氧化性能

氮氧化物(NO_x)是大气主要污染物之一, 主要来源于化石燃料的燃烧, 其中NO不溶于水难以去除, 催化氧化技术可以将NO氧化为易溶于水可被脱硫装置去除的NO₂, 具有十分重要的实际意义. 本文采用浸渍法制备了不同Mn掺杂量的Mn-Co/TiO₂复合金属氧化物催化剂, 考察了其催化NO氧化的活性. 结果表明, Mn的掺杂对Co/TiO₂催化剂催化NO氧化的活性有明显促进作用, 掺杂量为6%时, Mn(0.3)-Co(0.7)/TiO₂催化剂NO的转化效率最高, 300℃达到88%. 采用X射线衍射(XRD)、N₂吸附/脱附、H₂程序升温还原(H₂-TPR)、O₂程序升温脱附(O₂-TPD)和原位漫反射傅里叶变换红外(in-situ DRFTIR)光谱等技术对催化剂的物理化学特征进行了表征. 结果发现, 当掺杂量为6%时, Mn一方面促进了催化剂表面活性组分的分散, 增加了催化剂的比表面积和孔径; 另一方面提高了催化剂的还原性能, 促进氧的低温脱附, 此外还促进了反应中间产物桥式NO-3向NO₂的反应, 从而提高了Co/TiO₂催化剂的NO氧化活性.     

宽工作温度烟气脱硝催化剂制备及反应机理研究

以溶胶-凝胶法制备介孔TiO₂载体,采用分步浸渍法制备了V₂O₅-WO₃/TiO₂催化剂,借助BET、NH₃-TPD、H₂-TPR、SEM、活性评价、In-situ FT-IR等手段,考察了催化剂的结构、酸性、还原性、脱硝活性及反应机理等。介孔TiO₂载体比表面积为158.6 m²/g,制成催化剂后比表面积略有降低,约为136.7 m²/g。针对模拟烟气在φ_NH3/φ_NO=0.8的条件下测试催化剂的脱硝活性温度窗口为250~400 ℃,脱硝转化率达到80%。NH₃-TPD和H₂-TPR表征结果表明,催化剂在活性温度范围内具有典型的表面酸性位,载体TiO₂与V₂O₅之间存在的相互作用使得V₂O₅还原温度降低。利用In-situ FT-IR研究NH₃和NO在V₂O₅-WO₃/TiO₂催化剂表面吸附和氧化的反应过程发现,NH₃可同时吸附在L酸位和B酸位,NH₃在活性位上氧化脱氢形成NH₂物种是SCR脱硝反应的控制步骤。研究NO+O₂+NH₃反应时发现,吸附NH₃的催化剂引入NO和O₂后,共价吸附的NH₃首先消失。选择性催化还原反应发生在吸附态NH₃和气态或弱吸附态的NO之间,该反应遵从Eley-Rideal反应机理。     

Ce掺杂对碳纳米管负载Mn催化剂结构及SCR反应性能的影响

采用等体积浸渍法制备多壁碳纳米管(MWCNTs)负载Ce-Mn的催化剂,考察了Ce掺杂对Mn/MWCNTs催化剂上NH₃选择性催化还原(SCR)NO_x反应活性的影响.并运用透射电镜扫描、N₂吸附-脱附、程序升温还原、X射线光电子能谱、X射线衍射等手段,重点考察了Ce掺杂对Mn/MWCNTs催化剂结构性质的影响.结果表明,Ce掺杂能显著提高催化剂的SCR活性,其活性增量随着Ce含量的增加先增大后减小;当Ce/Mn为0.6时,催化剂活性最佳.表征结果显示,Mn/MWCNTs中添加Ce后,金属氧化物在MWCNTs上的分散程度提高;催化剂的比表面积和孔体积增大,平均孔径减小;氧化能力提高;表面氧含量增加,Mn化合价升高;结晶度降低,Mn主要以无定形或微晶形式存在,Ce主要以CeO₂物相存在.     

Promotional effect of Ce on the SCR of NO with NH<Subscript>3</Subscript> at low temperature over MnO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> supported by nitric acid-modified activated carbon

Different amounts of Mn and Ce oxides were loaded onto nitric acid-modified activated carbon (ACN) by wet impregnation. The series of catalysts were employed for the selective catalytic reduction of NO _x by NH₃ at temperatures between 100 and 250 °C. Cerium-modified catalysts exhibited higher de-NO _x performance than those modified with Mn/ACN, even with the same total loadings. The precursor solution with a molar ratio for Ce/(Mn + Ce) of 0.4 exhibited the highest catalytic activity. Enhanced resistance to SO₂ and H₂O and better stability were observed for 10%Mn–Ce(0.4)/ACN relative to 10%Mn/ACN. The catalysts were further characterized by N₂ physisorption, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), hydrogen temperature-programmed reduction (H₂-TPR), and temperature-programmed desorption of ammonia (NH₃-TPD). The N₂ physisorption and XRD results suggested that co-doping Ce with Mn increased the surface area and promoted the dispersion of Mn–Ce binary metal oxides. H₂-TPR the NH₃-TPD results demonstrated that the interaction between manganese oxide and cerium oxide species enhanced the redox and surface acidity of 10%Mn–Ce(0.4)/ACN.     

Activity enhancement of acetate precursor prepared on MnO_x-CeO_2 catalyst for low-temperature NH_3-SCR: Effect of gaseous acetone addition

MnO_x-CeO_2 catalysts are developed by hydrolysis driving redox method using acetate precursor(3 Mn1 Ce-Ac) and nitrate precursor(3 Mn1 Ce-N) for the selective catalytic reduction(SCR) of NO_x by NH_3.A counterpart sample(Cop-3 Mn1 Ce) was prepared by the NH_3·H_2 O co-precipitation method for comparison purpose.Combining the results of physicochemical properties characterization and performance test,we find that the 3 Mn1 Ce-Ac catalyst with some nanorod structures is highly active for the deNOx process.The SCR activity of the 3 Mn1 Ce-Ac catalyst is more admirable than the 3 Mn1 Ce-N and the Cop-3 Mn1 Ce catalysts due to plentiful Lewis acid sites,excellent low-temperature reducibility,and superior surface area resulted from O_2 generation during the pre paration procedure.The 3 Mn1 Ce-Ac still exhibits the greatest performance for the deNOx process when gaseous acetone is in the SCR feed gas.The NO_x conversion and N_2 selectivity over the 3 Mn1 Ce-Ac are both improved by gaseous acetone above150℃ due to the inhibition of SCR undesired side reactions(NSCR C-O reactions) and "slow-SCR" process.     

Chemical deactivation of Cu-SAPO-18 deNOx catalyst caused by basic inorganic contaminants in diesel exhaust

Contaminants (K, Na, Ca, and Mg) were introduced into Cu-SAPO-18 via incipient wetness impregnation to investigate their effect on the selective catalytic reduction of NO_x with NH₃ (NH₃-SCR) over Cu-SAPO-18. After the introduction of contaminants into Cu-SAPO-18, the quantity of acidic sites and Cu²⁺ species in catalyst decreases owing to the replacement of H⁺ and Cu²⁺ by K⁺, Na⁺, Ca²⁺, and Mg²⁺. Furthermore, the loss of isolated Cu^{2+ induces the generation of CuO and CuAl₂O₄-like phases, which causes further loss in the Brunauer-Emmett-Teller surface area of the catalyst. Consequently, the deNO_x performance of the contaminated Cu-SAPO-18 catalysts drops. Such decline in NH₃-SCR performance becomes more pronounced by increasing the contaminant contents from 0.5 to 1.0 mmol/g_catal. In addition, the deactivation influence of the contaminants on Cu-SAPO-18 is presented in the order of K> Na > Ca > Mg, which is consistent with the order of reduction of acidic sites. To a certain degree, the effect of the acidic sites on the deactivation of Cu-SAPO-18 might be more significant than that of isolated Cu2+ and the catalyst framework. Moreover, kinetic analysis of NH₃-SCR was conducted, and the results indicate that there is no influence of contaminants on the NH₃-SCR mechanism.}     

A study on simultaneous catalytic ozonation of Hg<Superscript>0</Superscript> and NO using Mn–TiO<Subscript>2</Subscript> catalyst at low flue gas temperatures

Mn–TiO₂ catalysts were utilized as an ozonation catalyst for the first time to study the simultaneous catalytic ozonation of Hg⁰ and NO at low flue gas temperatures. BET, SEM–EDS, XRD, XPS, H₂-TPR, NO _x -TPD and Hg⁰-TPD were used to characterize the catalysts. The Mn–TiO₂ catalyst, in which the molar content of metal Mn was 60%, exhibited the best catalytic activities of Hg⁰ and NO oxidation, compared with other Mn–TiO₂ catalysts. It was found that within the range of experiment, the catalytic ozonation efficiency of Hg⁰ and NO was higher than that of ozonation or catalytic oxidation. The results also showed that the presence of NO gas inhibited the catalytic ozonation of elemental mercury, and the inhibition was enhanced with the NO inlet concentration, while few elemental mercury molecules did promote the catalytic ozonation of NO. The addition of H₂O vapor promoted the catalytic ozonation of Hg⁰ and NO. In addition, 0.6Mn–TiO₂ catalyst demonstrated a good TOS and cyclic stability. The catalytic ozonation of NO and Hg⁰ on Mn–TiO₂ catalyst likely followed the Langmuir–Hinshelwood mechanism, where the hydroxyl radicals reacted with adjacently adsorbed NO molecules and elemental mercury on catalyst surface.     

Mn负载量对nMnO_x/TiO_2催化剂NH_3-SCR催化性能的影响

MnO_x/TiO_2催化剂由于具有优异的低温脱硝性能,已成为SCR催化剂的研究热点之一.我们通过浸渍法制备了一系列不同Mn负载量的nMnO_x/TiO_2(n=2.5%, 5%, 10%, 15%)(质量分数)催化剂,考察Mn负载量对催化剂脱硝性能的影响.利用N_2物理吸附, X-Ray Diffraction (XRD), Scanning Electron Microscope(SEM),Temperature Programmed Reduction with H_2(H_2-TPR),Temperature Programmed Desorption with NH_3(NH_3-TPD)和X-Ray Photoelectron Spectroscopy (XPS)对其结构进行表征.结果表明,催化剂的脱硝性能随着Mn负载量(2.5%～15%)(质量分数)的变化呈现"火山型"曲线,当Mn负载量为10%(质量分数)时,催化剂的脱硝性能最佳. H_2-TPR和XPS结果表明nMnO_x/TiO_2催化剂上表面氧比例和表面Mn~(4+)浓度均随着Mn负载量的增大,先增大后减小,具体顺序为10MnO_x/TiO_(2 ) 15MnO_x/TiO_(2 )5MnO_x/TiO_(2 ) 2.5MnO_x/TiO_2,与脱硝性能顺序完全一致.进一步关联表面氧的比例与T_(50)发现,催化剂的表面氧的比例与T_(50)呈线性关系,即表面氧比例越高, T_(50)越小,脱硝活性越高. NH_3-TPD结果表明,弱酸酸量的增加有助于低温脱硝活性的提高.这些结果揭示了Mn负载量影响脱硝性能的作用规律,为今后开发高效的锰基低温脱硝催化剂提供了技术支撑.