Review of Ag/Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-Reductant System in the Selective Catalytic Reduction of NO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>

Ag/Al₂O₃ is a promising catalyst for the selective catalytic reduction (SCR) by hydrocarbons (HC) of NO _x in both laboratory and diesel engine bench tests. New developments of the HC-SCR of NO _x over a Ag/Al₂O₃ catalyst are reviewed, including the efficiencies and sulfur tolerances of different Ag/Al₂O₃-reductant systems for the SCR of NO _x ; the low-temperature activity improvement of H₂-assisted HC-SCR of NO _x over Ag/Al₂O₃; and the application of a Ag/Al₂O₃-ethanol SCR system with a heavy-duty diesel engine. The discussions are focused on the reaction mechanisms of different Ag/Al₂O₃-reductant systems and H₂-assisted HC-SCR of NO _x over Ag/Al₂O₃. A SO₂-resistant surface structure in situ synthesized on Ag/Al₂O₃ by using ethanol as a reductant is proposed based on the study of the sulfate formation. These results provide new insight into the design of a high-efficiency NO _x reduction system. The diesel engine bench test results showed that a Ag/Al₂O₃-ethanol system is promising for catalytic cleaning of NO _x in diesel exhaust.     

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.     

Catalytically Promoted NOx Sorption by ZrO2-Based Oxides

Metal promoted zirconia-based oxide sorbents, such as Pt–ZrO₂/Al₂O₃ for NO _x have been investigated. To clarify the role of the catalyst component, sorption of NO and NO₂ was compared using the samples with and without Pt. The catalytic oxidation of NO to NO₂ and successively to nitrate ions is an important role for the Pt catalyst. The experimental results indicate that a high-temperature calcination is essential to remove residual Cl from Pt–ZrO₂–Al₂O₃ prepared from H₂PtCl₆ in order to provide more active NO _x sorption sites. Of M–ZrO₂–Al₂O₃ samples investigated, ruthenium as well as Pt demonstrated relatively good performance as a catalyst component in the sorbent. The FT-IR spectra after sorption of NO and NO₂ demonstrated a strong band attributed to stored nitrate ions. The Pt catalyst was more resistant to sulfur poisoning than a base metal catalyst. However, the NO _x sorptive capacities of the Pt–ZrO₂/Al₂O₃ sorbents were expected to be deteriorated in dilute SO₂ as far as observed from FT-IR spectra.     

Rhodium–Aluminum-Mixed Oxide Catalysts for Selective Reduction of NO x by Hydrocarbons

Rhodium—alumina-mixed oxides have been investigated as catalysts for selective catalytic reduction of NO _x by propene, as a part of the R&D Project of Next Generation Catalysts Research Institute. The results indicated that the NO _x reduction activity increases with a decrease in the reducibility of rhodium, suppressing wasteful consumption of propene by the reaction with oxygen. Coprecipitation method for the preparation of Rh-alumina catalysts was effective for the formation of the less-reducible rhodium sites, and the addition of zirconium and gallium further enhanced the formation of those sites and increased the selectivity of NO _x reduction.     

荧光XAFS表征Pt/BaAl2O4-Al2O3催化剂中的微量铂物种

随着稀薄燃烧(lean-burn)发动机的推广使用和环保法规的日趋严格,消除稀燃尾气中的氮氧化物(N O x)已刻不容缓。N O x储存还原技术被认为是最具应用前景的方法之一[1,2]。目前,对Pt/BaA l2O4-A l2O3体系中N O x储存与还原机制的研究较多[1￣4],但对该体系中微量铂物种微观结构及其与性能的关系研究较少,这主要是由于Pt含量(0.1w t%￣0.5wt%)太低,分散度较高,使表征方法受到很大限制。本文采用共沉淀-浸渍法制得具有较高比表面积和热稳定性的N O x储存还原催化剂Pt/BaA l2O4-A l2O3,应用荧光X-射线吸收精细结构方法(Fluores-cence-…     

Pt/MOx(M=Ni,Fe,Co,Ce)催化剂上CO氧化反应中抗H2O与CO2的性能研究

我们研究了4种负载型Pt催化剂（1Pt/NiO、1Pt/FeO_x、1Pt/Co₃O₄和Pt/CeO₂）上不同反应条件下CO氧化活性及抗H₂O和CO₂性能.发现反应气氛中CO₂的加入与CO形成了竞争吸附,并在催化剂表面形成了碳酸盐物种堵塞了活性位,从而导致催化剂失活.反应气氛中H₂O的加入对1Pt/CeO₂催化剂的活性有所抑制,但对1Pt/FeO_x、1Pt/NiO和1Pt/Co₃O₄催化剂的活性却有促进作用.在1Pt/FeO_x和1Pt/CeO₂催化剂上的分步反应实验和动力学研究表明,尽管H₂O的加入在两种催化剂上均与CO形成了竞争吸附,但在1Pt/FeO_x催化剂上H₂O在载体表面解离形成的羟基更易与CO反应,开辟了新的反应途径,从而提高了反应性能.此外,H₂O的加入能有效分解该催化剂上的碳酸盐物种,从而保持了其稳定性.     

用于NO_x低温下吸附还原的CoO_x/CeO_2二元氧化物的制备

研究了以多孔二氧化硅微球和活性炭为载体制备NOx吸附/还原催化剂的方法,摸索了最佳Ce/Co物质的量的比例。采用低温氮吸附方法测定了样品的BET比表面和孔容,利用XRD方法表征了样品中所掺杂的金属元素的晶型。研究发现:当nCe/nCo=75/25时,材料获得最佳NOx吸附能力,当以多孔二氧化硅微球作载体时,材料对于NOx的吸附主要来自CoOx和CeO2的二元氧化物;当以活性炭作为载体时,活性炭参与了NOx的吸附,因此其吸附容量大大提高。对NOx的吸附机理进行了探讨,并研究了样品的NH3还原性质。     

Pt-BaO催化剂的NOx储存-还原化学及结构-性能关系

NOx储存-还原(NSR)技术是目前稀燃汽车尾气中NOx消除的最有前景的催化技术之一,NSR催化过程中稀燃/富燃条件的交替运行、NSR催化剂上化学计量反应与催化反应的耦合赋予了NSR催化过程迥异于常规连续流动气固相催化反应的特点.本文首先介绍了目前人们对Pt-BaO催化剂上NSR基本化学过程的认识;在此基础上,结合本研...     

La1-xCaxMnO3纳米颗粒的制备及氧还原催化性能

本文采用溶胶凝胶法制备了一系列不同Ca含量的钙钛矿型氧化物La_1-xCa_xMnO₃(x=0~0.4)纳米颗粒, X射线粉末衍射及精修、扫描电镜表征显示其相纯度和结晶度高, 颗粒平均粒径约40 nm。在0.1 mol·L^-1 KOH水溶液中进行的氧还原电催化性能测试显示, La_0.7Ca_0.3MnO₃样品催化活性最高, 表观电子转移数接近4, 还原电流密度与Pt/C催化剂相当, 而催化稳定性优于Pt/C。进一步研究了La_1-xCa_xMnO₃样品中Mn价态、晶胞参数的改变对氧还原催化活性的影响, 结果表明当x=0.3时, 催化剂中Mn处于混合价态, Mn-O键长适中, 最有利于电催化反应。     

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.     

La1-xCaxMnO3纳米颗粒的制备及氧还原催化性能

本文采用溶胶凝胶法制备了一系列不同Ca含量的钙钛矿型氧化物La1-xCaxMnO3(x=0~0.4)纳米颗粒,X射线粉末衍射及精修、扫描电镜表征显示其相纯度和结晶度高,颗粒平均粒径约40 nm。在0.1 mol.L-1KOH水溶液中进行的氧还原电催化性能测试显示,La0.7Ca0.3MnO3样品催化活性最高,表观电子转移数接近4,还原电流密度与Pt/C催化剂相当,而催化稳定性优于Pt/C。进一步研究了La1-xCaxMnO3样品中Mn价态、晶胞参数的改变对氧还原催化活性的影响,结果表明当x=0.3时,催化剂中Mn处于混合价态,Mn-O键长适中,最有利于电催化反应。     

By-Products NOx Control and Performance Improvement of a Packed-Bed Nonthermal Plasma Reactor

NO_x are main toxic by-products in the effluent gas whendecomposing volatile organic compounds in air by a packed-bed plasmareactor. Several types of materials such as 13X zeolite, BaTiO₃and Pd/Pt catalysts have been selected to be packed in the reactor, andmethane decomposition and NOx by-products in discharged gases areinvestigated at different range of reaction temperature and dischargeenergy density at atmospheric pressure. The ratios of methane decompositionpercentage/NO_x concentration are used to assess these packed bedmaterials and reaction conditions. The results show that usingPd/-Al₂O₃ with lower percentage Pd as packedbed, and discharging with lower discharge density at higher reactiontemperature can reduce NO_x output effectively and greatly improveperformance of the reactor.     

Selective hydrogenation of o-chloronitrobenzene (o-CNB) over supported Pt and Pd catalysts obtained by laser vaporization deposition of bulk metals

Carbon nanotubes (CNTs), γ-alumina (γ-Al₂O₃) and silica (SiO₂) supported Pt and Pd catalysts were produced by laser vaporization deposition of respective bulk metals. The catalysts were characterized by inductive coupled plasma emission spectrometer (ICP), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). The catalytic properties of the catalysts were investigated in the liquid phase hydrogenation of o-chloronitrobenzene (o-CNB) to o-chloroaniline (o-CAN) under 333 K and 1.0 MPa hydrogen pressure. The results show that the catalytic properties are greatly affected by the supports. Pt/CNTs catalyst exhibits the best catalytic performance among the Pt-based catalysts, producing o-CAN with 99.6% selectivity at complete conversion. Pd/CNTs catalyst exhibits the best catalytic performance among the Pd-based catalysts, giving o-CAN with 95.2% selectivity at complete conversion. For Pt-based catalysts, geometric effect and the textures and properties of the supports play important roles on catalytic properties. On the other hand, geometric effect, electronic effect and the textures and properties of the supports simultaneously influence the catalytic properties of the Pd-based catalysts. In addition, hydrogenolysis of the C–Cl bond can be well inhibited over all catalysts prepared by laser vaporization deposition.     

In situ X-ray diffraction study of reduction processes of Fe3O4- and Fe1−xO-based ammonia-synthesis catalysts

The temperature-programmed reduction process of two types of industrial ammonia-synthesis catalysts, A110 and ZA-5, which are, respectively, based on Fe₃O₄ and Fe_1−xO precursors, were studied by in situ X-ray power diffraction (XRD). It has been found that the ZA-5 has lower reduction temperature and faster reduction rate, and its active phase α-Fe possesses a higher value of lattice microstrain than A110. The simulation based on Rietveld refinement has also shown that the shape of α-Fe grain of ZA-5 has a mixed shape of cube and sphere with more exposing (111) and (211) planes, while that of A110 looks like a concave cube with more exposing (110) planes. Based on the results obtained, a growth model of α-Fe during the reduction of Fe₃O₄- and Fe_1−xO-based ammonia-synthesis catalysts is proposed, and the origins for the activity difference has been also discussed.     

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。     

相转移法制备PdMo催化剂及其氧还原活性

以四丁基氢氧化铵作为相转移剂,以硼氢化钠为还原剂,利用相转移法在二氯甲烷中制备了一系列不同比例的Pd_xMo/C(Pd/Mo的原子比x=1、2、3、4、5)催化剂。透射电镜(TEM)图像显示,Pd_x Mo/C是呈2～4 nm的圆形颗粒,尺寸均匀、分散性良好。X射线衍射(XRD)结果表明,加入第二组元Mo后,Pd的晶格发生扩张,调节了 Pd的几何结构。此外,X射线光电子能谱(XPS)结果表明,相对于Pd/C,Pd_4Mo/C的Pd3d_(5/)2结合能负移了 0.50 eV,说明电负性较大的Pd从Mo吸电子,电子结构发生改变。氧还原反应(ORR)结果表明,不同比例的Pd_xMo/C催化剂活性均优于Pd/C,其中当x=4时,ORR活性最佳,其起始电位和半波电位分别为0.876和0.813 V,高于商业Pt/C的0.870和0.810 V。此外,在经过3 h的运行之后电流密度仍保留82.9%,与商业Pt/C相比具有明显的优势。     

低于300℃时两种氧化铈材料对稀燃阶段NOx存储性能的影响

研究了低于300 ℃时两种氧化铈对稀燃阶段NO_x存储性能的影响,催化剂由2%（w）Pt/Al₂O₃（PA）与CeO₂-X（X=S,I）机械混合制备. X射线衍射（XRD）,BET表面积和扫描电子显微镜（SEM）用于表征材料的物理结构. X射线光电子能谱（XPS）和H₂程序升温还原（H₂-TPR）用于表面Ce³⁺和活性氧定量. 原位漫反射傅里叶变换红外光谱（in-situ DRIFTS）用于分析表面NO_x吸附物种. 相比于CeO₂-I,CeO₂-S 具有优良的物理化学性能,包括高比表面积、丰富的空隙结构、较高的抗老化能力及表面Ce³⁺浓度. 因而,Pt/Al₂O₃+CeO₂-S 表现出优异的NO_x存储能力. 此外,PA+CeO₂-X（X=S,I）上存在Pt 与CeO₂之间的相互作用,可提高表面氧物种的活性进而促进NO氧化及NO_x存储. PA+CeO₂-S上的这种相互作用要强于PA+CeO₂-I. 研究表明,表面Ce³⁺浓度和活性氧含量对NO_x存储起到重要作用. 然而经过水热处理后,Pt 与老化的氧化铈（ACS,ACI）之间的相互作用降低,并且两种氧化铈NO_x存储性能显著下降. 另外,与PA+ACS（ACI）相比,PA+PACS（PACI）样品NO_x存储能力得到改善,这归因于表面氧物种活性增加能促进硝酸盐的形成.     

Methods to enhance tolerances of Chlorella KR-1 to toxic compounds in flue gas

Possible methods to minimize the toxic effects of SO _x and NO _x on the growth of a highly CO₂ tolerant and fast-growing microalga, Chlorella sp. KR-1, were investigated. Maintaining the pH of the culturing media at an adequate value was quite important to enhancing the tolerances of the microalgae to SO _x and NO _x . Controlling the pH by adding an alkaline solution, using a low flow rate of gas fed to the culture, and using a high concentration of inoculating cells were effective methods to maintaining the proper pH of the culture. Controlling the pH was the most effective method but could be applied only for some specific microalgae.     

X-ray photoelectron spectroscopic study of the interaction of supported metal catalysts with NO<Subscript>x</Subscript>

The reactions of the platinum and rhodium model catalysts applied to aluminum oxide with NO_x (10 Torr NO + 10 Torr O₂) were studied by X-ray photoelectron spectroscopy. The reaction conducted at room temperature formed on the surface of the oxide support the NO _3,s ^? nitrate ions characterized by the N1s line at 407.4 eV and O1s line at 533.1 eV and the NO _2,s ^? nitrite ions characterized by the N1s line with a binding energy of 404.7 eV. At the same time, the Pt4f and Rh3d lines of the supported platinum particles are shifted toward higher binding energies by 0.5–1.0 eV and 0.7–1.2 eV, respectively. It is assumed that the binding energies increase due to changes in the chemical state of the platinum metal in which oxygen is dissolved. The reaction of NO_x with Pt/Al₂O₃ at 200°C forms platinum oxide defined by the Pt4f _7/2 line with a binding energy of 72.3 eV.