Catalytic Performance of Spherical MCM-41 Modified with Copper and Iron as Catalysts of NH3-SCR Process

Spherical MCM-41 with various copper and iron loadings was prepared by surfactant directed co-condensation method. The obtained samples were characterized with respect to their structure (X-ray diffraction, XRD), texture (N₂ sorption), morphology (scanning electron microscopy, SEM), chemical composition (inductively coupled plasma optical emission spectrometry, ICP-OES), surface acidity (temperature programmed desorption of ammonia, NH₃-TPD), form, and aggregation of iron and copper species (diffuse reflectance UV-Vis spectroscopy, UV-Vis DRS) as well as their reducibility (temperature programmed reduction with hydrogen, H₂-TPR). The spherical MCM-41 samples modified with transition metals were tested as catalysts of selective catalytic reduction of NO with ammonia (NH₃-SCR). Copper containing catalysts presented high catalytic activity at low-temperature NH₃-SCR with a very high selectivity to nitrogen, which is desired reaction products. Similar results were obtained for iron containing catalysts, however in this case the loadings and forms of iron incorporated into silica samples very strongly influenced catalytic performance of the studied samples. The efficiency of the NH₃-SCR process at higher temperatures was significantly limited by the side reaction of direct ammonia oxidation. The reactivity of ammonia molecules chemisorbed on the catalysts surface in NO reduction (NH₃-SCR) and their selective oxidation (NH₃-SCO) was verified by temperature-programmed surface reactions.     

Comparative Study of the Support Role on the Activity of Copper Species for Nitric Oxide Reduction

In this work three different supports (γ-Al₂O₃, ZSM-5, and SAPO-34) of varying degree of acid sites and textural properties were used to evaluate the influence of support specifics in the Cu/supported nanocatalysts on NO conversion. The nanocatalysts were prepared by homogeneous deposition precipitation (HDP) method and characterized by N₂ pore size distribution, TEM, H₂-TPR for investigation the reducibility of the copper species and acidity measurement by NH₃ adsorption. The Cu/ZSM-5 and Cu/SAPO-34 catalysts were more active for NO conversion than Cu/γ-Al₂O₃ catalyst. The characterization and conversion differences in the copper supported on different types of support indicated that these differences arise from the differences in surface area, pore size distribution, and acidity of the supports. The higher SCR-DeNO activity of Cu/ZSM-5 and Cu/SAPO-34 nano-catalysts can be explained by higher surface area and acidity of ZSM-5 and SAPO-34 supports. These catalysts also have larger amount of reducible Cu species compared to Cu/γ-Al₂O₃ which correlates with the structure of the support used. Considering these findings, the NO conversion ability of Cu/supported catalysts has been correlated with support structure and acidity.     

Ammoxidation of 3-picoline to nicotinonitrile using silica-supported VCrO catalysts

A series of vanadium–chromium oxide (VCrO) catalysts supported on silica was prepared by wetness impregnation method with different Cr/V molar ratios from 0.2 to 1.0. These catalysts were characterized by XRD, TG, temperature-programmed desorption of ammonia (NH₃-TPD), X-ray photoelectron spectra (XPS), and Raman spectroscopy, and their catalytic activity was evaluated in the ammoxidation of 3-picoline (3-PIC) to nicotinonitrile (NN). The results of XRD, TG, Raman, and XPS confirmed that the active components on the silica surface were mainly amorphous V₂O₅ and CrVO₄. The results of NH₃-TPD showed that acidity of the catalysts decreased with the increase of Cr/V ratio. Catalytic results revealed that acidity of the catalysts was closely related to the catalytic performance. Low acidity gave low conversion of 3-PIC and high NN selectivity. Furthermore, the conversion of 3-PIC increased with rise in reaction temperature, and the selectivity of NN was slightly influenced by the 3-PIC conversion. Therefore, among the catalysts (Cr/V ratio was 0.2, 0.4, 0.6) tested, Cr/V-0.6 catalyst retained the lowest acidity and exhibited the highest selectivity and yield of NN in the ammoxidation of 3-PIC.     

Ho改性的Mn-Ce/TiO2催化剂低温脱硝性能的评价和表征

作为引起酸雨、光化学烟雾、雾霾等大气污染问题的主要根源,氮氧化物(NOx)的防治已成为亟待解决的问题.选择性催化还原技术作为最成熟有效的脱硝技术,目前已经被广泛应用于各燃煤电厂.低温脱硝催化剂具有优秀的低温活性,使得脱硝装置可以安放在脱硫装置和除尘装置下游,受到了学者广泛的研究.目前低温脱硝催化剂的研究主要是对催化剂进行改性以提高催化剂的性能,已有许多研究报道了Sn、Ni、Co、Zr、Cr、Ni等对催化剂的改性影响.Ho作为一种改性元素被应用于光催化领域,能提高TiO2的光催化能力.但Ho应用于脱硝领域的研究鲜有报道,其氧化物具有酸性位点有助于脱硝反应,因此研究Ho对低温SCR催化剂的改性作用具有重要意义.本文采用浸渍法制备Ho掺杂的Mn-Ce/TiO2催化剂,研究了Ho的掺杂对于Mn-Ce/TiO2催化剂低温脱硝性能的影响,同时还研究了烟气中的SO2和H2O对催化剂活性的影响,并利用XPS、XRD、H2-TPR、NH3-TPD等表征方法从物理性质和化学性质两方面对Ho改性的影响机理进行了研究.研究发现,Ho的掺杂能提高Mn-Ce/TiO2催化剂的脱硝能力,有助于催化剂N2选择性的提高.分析表明,Ho的掺杂有助于催化剂比表面积的提升,且能提高催化剂的酸性,有利于催化剂对NH3的吸附,从而提高催化剂的性能.XPS表征结果表明Ho掺杂后的催化剂具有更高的化学吸附氧浓度和较高的Mn4+/Mn3+比例, 使得脱硝反应更容易进行.改性后催化剂的抗水抗硫实验结果表明,Ho的掺杂能够提高催化剂的抗水抗硫性能.XRD结果表明,抗水抗硫实验后催化剂表面形成了硫酸铵盐,硫酸铵盐的形成会堵塞催化剂表面的活性位,限制脱硝反应的进行,从而影响催化剂的脱硝活性.同时,400°C下进行再生实验后的催化剂活性有所恢复,但是未能达到抗水抗硫实验前的活性,表明在抗水抗硫实验中催化剂表面形成了除硫酸铵盐以外的其他硫酸盐类.结合XPS和XRD表征结果,推断生成的盐类物质为硫酸锰和硫酸铈,从而导致再生后的催化剂的脱硝活性无法恢复到最初的活性水平.由此可以看出,硫酸盐的形成是催化剂在含硫气氛中失活的主要原因.     

低硅铝比ZSM-5分子筛的合成及其正庚烷裂化反应性能

以氨水为矿化剂,通过添加NH₄⁺离子水热合成了具有较低骨架硅铝比的ZSM-5分子筛。通过X射线衍射(XRD)、扫描电镜(SEM)、固体核磁共振(MAS-NMR)等表征手段,研究了硅源、铝源、矿化剂、阳离子等对ZSM-5分子筛的结晶度、形貌尺寸和骨架硅铝比等的影响,研究了ZSM-5分子筛的骨架硅铝比对正庚烷催化裂化反应的影响。研究表明,投料硅铝比越低,铝原子越难进入到分子筛骨架中;当氨水为矿化剂、正硅酸四乙酯为硅源时可以合成骨架硅铝比较低的氢型ZSM-5分子筛,添加NH₄⁺离子可以增强骨架铝的嵌入,进一步降低分子筛的骨架硅铝比(24.2)。正庚烷裂化反应结果表明,降低分子筛的骨架硅铝比可以提高正庚烷裂化反应的活性,但会降低低碳烯烃的选择性。     

硫酸化对CeO2-ZrO2催化剂上NH3选择催化还原NO反应的影响

由发电厂等固定源和柴油机等移动源排放的一氧化氮(NO)造成的环境污染问题日益严重.随着严苛的排放法规出台,NO排放控制技术受到越来越多关注.NH3选择性催化还原(SCR)技术是目前去除NO应用最为广泛的方法之一.商业催化剂V2O5-WO3/TiO2在300–400℃温度窗口内显示出优越的NO去除效率,但仍存在一些问题,如钒氧化物的毒性以及在高温时形成N2O和SO3.因此,开发出低钒或无钒的新型催化剂是解决上述问题的关键.CeO2和含铈材料是重要的催化剂载体,具有良好的还原能力和氧存储功能,因而广泛应用于催化领域.CeO2添加到商用催化剂中不仅可以降低钒用量,而且可以提高催化剂抗碱金属中毒能力.CeO2-WO3催化剂在200℃以上时比商用催化剂具有更宽的温度窗口,并展现出较高的抗SO2和碱金属中毒能力.CeO2-ZrO2催化剂通过添加过渡金属元素可以提升其SCR活性,在较宽的温度窗口内具有较高的催化活性.废气中SO2可导致催化剂失活,在实际应用中催化剂硫中毒是较为常见的催化剂失效原因.通常情况下,锰基和铁基催化剂最容易硫中毒.然而CeO2催化剂在硫酸化处理后却展现出良好的SCR活性.催化剂硫酸化主要包括气相、液相和前驱体硫化三种方法.三种方法各有异同,但在催化剂表面形成的硫物种都是SO42–.硫酸化可以增强Ce基催化剂的SCR活性,但是对于硫化引起的催化剂表面酸性、氧化还原性以及NO吸附脱附性质的详细研究报道较少.本文通过液相法对CeO2-ZrO2(CeZr)催化剂进行了硫酸化.XRD结果表明,硫酸化并未对催化剂结晶结构产生影响.TPD和TPR结果表明,硫酸化后催化剂(S-CeZr)表面酸性增强,但抑制了其氧化性.通过原位红外光谱技术系统研究了催化剂在SCR反应过程中表面物种的变化,结果发现,CeZr和S-CeZr的催化机理相同,不同的SCR活性主要是由表面酸性和氧化性引起的.CeO2基催化剂在不同温度窗口遵循不同反应机理.CeZr催化剂具有较强的氧化还原性,使其对NO和NH3具有很强的氧化能力,所以其在低于200℃时具有较好的SCR活性.而S-CeZr催化剂具有更多的Br?nsted酸性位,导致NO不易吸附在催化剂表面,所以其在低温时SCR活性较差,但在高温时(>200℃)具有优良的SCR活性.通过SCR活性和反应机理研究,发现在高温时(>200℃),表面酸性尤其是强酸Br?nsted酸性位在SCR反应中起到决定性作用;而在低温时(<200℃),酸性位对NH3分子较强的键合作用导致NH3难以被氧化,所以较强的酸性位对SCR活性具有抑制作用,而氧化还原性在低温时对SCR反应起到主要作用.同时,在高温时,较高的氧化性可使NH3被O2直接氧化,导致N2选择性降低.     

Heats of Adsorption of Ammonia and Correlation of Activity and Acidity in Heterogeneous Catalysis

Adsorption microcalorimetry was applied to determine heats of adsorption of ammonia on zeolites Y, mordenite, ZSM-5, heteropolyacid H₃PW₁₂O₄₀, as well as silica gel and amorphous aluminosilicates. The plots of differential heats against coverage served to construct the acidity spectra and, in this way, to determine the number of acid sites with different acidity strengths. The behavior of these materials in acid-catalyzed reactions, primarily, in the transformations of hydrocarbons is discussed. Evidence is presented that heats of adsorption of ammonia can be used to obtain correlation plots that describe relations between acidic and catalytic properties of zeolite catalysts.     

Selective Catalytic Reduction of Nitric Oxide by Ammonia over Ag and Zn‐Exchanged Cuban Natural Zeolites

The catalytic selective reduction of NO over metal‐exchanged (Zn^II, Ag^I) natural zeolites (mordenite and clinoptilolite) from Cuba using NH₃ as a reducing agent in the presence of excess oxygen was studied. Both transition metals slightly improve the catalytic performance for the NO reduction. Zn^II‐exchanged zeolites exhibit a moderate catalytic activity, with conversions of NO of ≈58 % and high selectivity to N₂ at high temperatures.     

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.     

Progress on Noble Metal-Based Catalysts Dedicated to the Selective Catalytic Ammonia Oxidation into Nitrogen and Water Vapor (NH3-SCO)

A recent development for selective ammonia oxidation into nitrogen and water vapor (NH₃-SCO) over noble metal-based catalysts is covered in the mini-review. As ammonia (NH₃) can harm human health and the environment, it led to stringent regulations by environmental agencies around the world. With the enforcement of the Euro VI emission standards, in which a limitation for NH₃ emissions is proposed, NH₃ emissions are becoming more and more of a concern. Noble metal-based catalysts (i.e., in the metallic form, noble metals supported on metal oxides or ion-exchanged zeolites, etc.) were rapidly found to possess high catalytic activity for NH₃ oxidation at low temperatures. Thus, a comprehensive discussion of property-activity correlations of the noble-based catalysts, including Pt-, Pd-, Ag- and Au-, Ru-based catalysts is given. Furthermore, due to the relatively narrow operating temperature window of full NH₃ conversion, high selectivity to N₂O and NO_x as well as high costs of noble metal-based catalysts, recent developments are aimed at combining the advantages of noble metals and transition metals. Thus, also a brief overview is provided about the design of the bifunctional catalysts (i.e., as dual-layer catalysts, mixed form (mechanical mixture), hybrid catalysts having dual-layer and mixed catalysts, core-shell structure, etc.). Finally, the general conclusions together with a discussion of promising research directions are provided.     

Effect of copper precursors on the catalytic activity of Cu/ZSM-5 catalysts for selective catalytic reduction of NO by NH<Subscript>3</Subscript>

The Cu/ZSM-5 catalysts prepared by different copper precursors were used for the selective catalytic reduction (SCR) of NO _x with NH₃. The Cu/ZSM-5 catalyst prepared by the copper nitrate (Cu/ZSM-5-N) presented the best performance among the Cu/ZSM-5 catalysts and showed above 90 % NO _x conversion at 225–405 °C. The average particle size of CuO was 5.82, 9.20, and 11.01 nm over Cu/ZSM-5-N, Cu/ZSM-5-S (prepared by copper sulfate), and Cu/ZSM-5-C (prepared by copper chloride), respectively. The Cu/ZSM-5-N catalyst showed the highly dispersed copper species, the strong surface acidity, and the excellent redox ability compared with the Cu/ZSM-5-C and Cu/ZSM-5-S catalysts. The Cu⁺ and Cu²⁺ existed in the Cu/ZSM-5 catalysts and the abundant Cu⁺ over Cu/ZSM-5-N might be responsible for the superior SCR activity.     

ZSM-5分子筛的合成及其在丁烯催化裂解反应中的应用

采用水热合成法制备了无模板剂ZSM-5分子筛并用正硅酸甲酯(TMOS)对其进行外表面修饰改性,利用XRD、SEM、~(29)Si MAS NMR、~(27)Al MAS NMR、NH_3-TPD、BET和UV-vis DRS对合成分子筛的物相、形貌和酸性等进行了表征,并将其应用于催化丁烯裂解反应。研究表明,经水热合成的无模板剂ZSM-5结晶度较好,与添加模板剂合成的ZSM-5拥有相似的孔道结构和晶体结构以及相近的酸量,但在酸中心分布上有明显差异:孔道内酸中心数量增加且分布更加均匀,孔道交叉处酸中心数量减少;经过外表面修饰改性后,ZSM-5分子筛外表面部分不具备择形性的酸中心被钝化,使其择形选择能力增强。在催化丁烯裂解反应中,用TMOS进行外表面修饰改性的无模板剂ZSM-5分子筛作为催化剂能够有效抑制副反应的发生,丙烯和乙烯的总收率高达58%。     

Conjugate Conversion of Methanol and Lower Alkanes C3-C4 on Zeolite-Containing Catalysts

Simultaneous conversion of methanol and lower alkanes C₃-C₄ on high-silica zeolites of ZSM-5 type of various compositions (SiO₂/Al₂O₃ 30, 50, 90) was studied. The catalytic activity of zeolite catalysts and their physicochemical properties (acidity, sorption capacity, and pore structure) were evaluated.     

Praseodymium Oxide Modified CeO2/Al2O3 Catalyst for Selective Catalytic Reduction of NO by NH3

A series of CeO₂/Al₂O₃ catalysts was modified with praseodymium oxide using an extrusion method. The catalytic activities of the obtained catalysts were measured for the selective catalytic reduction of NO with NH₃ to screen suitable addition of praseodymium oxide. These samples were characterized by XRD, N₂‐BET, NH₃‐TPD, NO‐TPD, Py‐IR, H₂‐TPR, Raman spectra and XPS, respectively. Results showed the optimal catalyst with the Pr/Ce molar ratio of 0.10 exhibited more than 90% NO conversion in a wide temperature range of 290–425°C under GHSV of 5000 h^?1. The number of Lewis acid sites and the chemisorbed oxygen concentration of the catalysts would increase with the Pr incorporation, which was favorable for the excellent catalytic performance. In addition, the Pr incorporation inhibited growth of the Al₂O₃ crystal particles and led to the lattice expansion of CeO₂, which increased catalytic activity. The results implied that the higher chemisorbed oxygen concentrations and the more Lewis acid sites were conductive to obtain the excellent SCR activity.     

Catalytic Oxidation of CO and Benzene over Metal Nanoparticles Loaded on Hierarchical MFI Zeolite

In order to obtain highly active catalytic materials for oxidation of carbon monoxide and volatile organic compounds (VOCs), monometallic platinum, copper, and palladium catalysts were prepared by using of two types of ZSM-5 zeolite as supports—parent ZSM-5 and the same one treated by HF and NH₄F buffer solution. The catalyst samples, obtained by loading of platinum, palladium, and copper on ZSM-5 zeolite treated using HF and NH₄F buffer solution, were more active in the reaction of CO and benzene oxidation compared with catalyst samples containing untreated zeolite. The presence of secondary mesoporosity played a positive role in increasing the catalytic activity due to improved reactant diffusion. The only exception was the copper catalysts in the reaction of CO oxidation, in which case the catalyst, based on untreated ZSM-5 zeolite, was more active. In this specific case, the key role is played by the oxidative state of copper species loaded on the ZSM-5 zeolites.     

Comparative study of Co3O4-ZSM-5 catalysts synthesized by different hydrothermal methods for the catalytic oxidation of dichloromethane

In this work, various Co₃O₄-ZSM-5 catalysts were prepared by the microwave hydrothermal method (MH-Co₃O₄@ZSM-5), dynamic hydrothermal method (DH-Co₃O₄@ZSM-5), and conventional hydrothermal method (CH-Co₃O₄/ZSM-5). Their catalytic oxidation of dichloromethane (DCM) was analyzed. Detailed characterizations such as X-ray diffractometer (XRD), scanning microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Brunauer–Emmett–Teller (BET), H₂ temperature-programmed reduction (H₂-TPR), temperature-programmed desorption of O₂ (O₂-TPD), temperature-programmed desorption of NH₃ (NH₃-TPD), diffuse reflectance infrared Fourier-transform spectra with NH₃ molecules (NH₃-DRIFT), and temperature-programmed surface reaction (TPSR) were performed. Results showed that with the assistance of microwave, MH-Co₃O₄@ZSM-5 formed a uniform core-shell structure, while the other two samples did not. MH-Co₃O₄@ZSM-5 possessed rich surface adsorbed oxygen species, higher ratio of Co³⁺/Co²⁺, strong acidity, high reducibility, and oxygen mobility among the three Co₃O₄-ZSM-5 catalysts, which was beneficial for the improvement of DCM oxidation. In the oxidation of dichloromethane, MH-Co₃O₄@ZSM-5 presented the best activity and mineralization, which was consistent with the characterizations results. Meanwhile, according to the TPSR test, HCl or Cl₂ removal from the catalyst surface was also promoted in MH-Co₃O₄@ZSM-5 by their abundant Brønsted acid sites and the promotion of Deacon reaction by Co₃O₄ or the synergistic effect of Co₃O₄ and ZSM-5. According to the results of in situ DRIFT studies, a possible reaction pathway of DCM oxidation was proposed over the MH-Co₃O₄@ZSM-5 catalysts.     

Catalytic Performance of One-Pot Synthesized Fe-MWW Layered Zeolites (MCM-22, MCM-36, and ITQ-2) in Selective Catalytic Reduction of Nitrogen Oxides with Ammonia

The application of layered zeolites of MWW topology in environmental catalysis has attracted growing attention in recent years; however, only a few studies have explored their performance in selective catalytic reduction with ammonia (NH₃-SCR). Thus, our work describes, for the first time, the one-pot synthesis of Fe-modified NH₃-SCR catalysts supported on MCM-22, MCM-36, and ITQ-2. The calculated chemical composition of the materials was Si/Al of 30 and 5 wt.% of Fe. The reported results indicated a correlation between the arrangement of MWW layers and the form of iron in the zeolitic structure. We have observed that one-pot synthesis resulted in high dispersion of Fe³⁺ sites, which significantly enhanced low-temperature activity and prevented N₂O generation during the reaction. All of the investigated samples exhibited almost 100% NO conversion at 250 °C. The most satisfactory activity was exhibited by Fe-modified MCM-36, since 50% of NO reduction was obtained at 150 °C for this catalyst. This effect can be explained by the abundance of isolated Fe³⁺ species, which are active in low-temperature NH₃-SCR. Additionally, SiO₂ pillars present in MCM-36 provided an additional surface for the deposition of the active phase.     

共沉淀法和浸渍法制备的HoCeMn/TiO2催化剂的脱硝性能

采用浸渍法和共沉淀法制备了Ho Ce Mn/Ti O₂脱硝催化剂并对其结构和性能进行了表征。结果表明共沉淀法增强了活性组分和载体的相互作用,从而增加了Ho Ce Mn Ti-C催化剂表面Ce³⁺、Mn⁴⁺以及吸附氧的含量,使其表现出优异的低温氧化还原性能。此外,共沉淀法制备的HoCeMnTi-C具有更多的表面酸性位点及更强的表面酸性。催化剂表面酸性和氧化还原性能的提高有助于氨的吸附和活化,从而显著提高其活性。表面酸性位点的增多还抑制了H₂O和SO₂在催化剂表面的吸附,提升了催化剂的抗水抗硫性能。催化剂上的选择性催化还原(SCR)反应遵循Eley-Rideal(E-R)机制,催化剂硫中毒是源于形成的硫酸盐覆盖或破坏了催化剂活性位。     

富氧条件下Co/ZSM-5催化剂对C_3H_8选择还原NO_x的性能

采用多种物理化学手段研究了在模拟的轻型柴油车尾气中不同Co担载量及Cu掺杂的Co/ZSM-5催化剂的Co组分分散状态、可还原性、NO吸附脱附性质对C3H8选择性催化还原NOx性能的影响。结果表明,浸渍法制备的Co/ZSM-5催化剂上既有外表面上的Co3+和Co2+物种,也有孔内的Co2+离子。富氧条件下Co/ZSM-5催化剂上C3H8选择性催化还原NOx的活性主要与ZSM-5载体孔外表面分散的CoOx物种中的钴离子可还原能力和NO吸附脱附性能密切相关。Co/ZSM-5催化剂上适宜的Co担载量约为4.0wt%,低担载量时随Co担载量增加,表面CoOx物种中钴离子可还原能力增强,C3H8选择性催化还原NOx的低温转化活性增加;高担载量时,随Co担载量增加,单位Co离子的NO吸附量的减少以及催化剂表面活性中心数的减少,导致了Co/ZSM-5催化剂NOx的转化率和催化剂比速率(k)的下降。孔外表面Co3O4晶体的存在使催化剂表面产生较强的NO吸附,并在高温时有利于C3H8的氧化燃烧,使C3H8选择性催化还原NOx的活性降低。     

富氧条件下Co/ZSM-5催化剂对C3H8选择还原NOx的性能

采用多种物理化学手段研究了在模拟的轻型柴油车尾气中不同Co担载量及Cu掺杂的Co/ZSM-5催化剂的Co组分分散状态、可还原性、NO吸附脱附性质对C₃H₈选择性催化还原NO_x性能的影响。结果表明,浸渍法制备的Co/ZSM-5催化剂上既有外表面上的Co³⁺和Co²⁺物种,也有孔内的Co²⁺离子。富氧条件下Co/ZSM-5催化剂上C₃H₈选择性催化还原NO_x的活性主要与ZSM-5载体孔外表面分散的CoO_x物种中的钴离子可还原能力和NO吸附脱附性能密切相关。Co/ZSM-5催化剂上适宜的Co担载量约为4.0wt%,低担载量时随Co担载量增加,表面CoO_x物种中钴离子可还原能力增强,C₃H₈选择性催化还原NO_x的低温转化活性增加;高担载量时,随Co担载量增加,单位Co离子的NO吸附量的减少以及催化剂表面活性中心数的减少,导致了Co/ZSM-5催化剂NO_x的转化率和催化剂比速率（k）的下降。孔外表面Co₃O₄晶体的存在使催化剂表面产生较强的NO吸附,并在高温时有利于C₃H₈的氧化燃烧,使C₃H₈选择性催化还原NO_x的活性降低。