NO在碳纳米管(CNTs),Rh/CNTs,Rh/Al_2O_3上的分解(英文)

甲烷在预还原的ＬａＣｏＯ３催化剂上分解生成碳纳米管（ＣＮＴｓ）。研究了稳态下ＮＯ在ＣＮＴｓ,Ｒｈ／ＣＮＴｓ,Ｒｈ／Ａ１２Ｏ３上的分解,温度区间为５７３Ｋ～９７３Ｋ,原料气为６０００ｐｐｍ的ＮＯ,Ｈｅ为平衡气。程序升温还原结果表明：（１）Ｒｈ的负载显著降低了ＣＮＴｓ的氢吸收量;（２）负载于ＣＮＴｓ上的Ｒｈ比负载于Ａ１２Ｏ３上的Ｒｈ更易还原。在５７３Ｋ时ＮＯ即能与预还原后的ＣＮＴｓ,Ｒｈ／ＣＮＴＳ,Ｒｈ／Ａｌ２Ｏ３中存储的氢反应;随着氢的消耗,反应活性逐渐降低,当储存的氢消耗完后,ＮＯ的直接催化反应发生。在８７３ Ｋ及以上,Ｒｈ／ＣＮＴｓ中的ＣＮＴｓ能彼ＮＯ分解产生的氧氧化为ＣＯ。在９７３Ｋ时,ＮＯ在ＣＮＴｓ上几乎能１００％分解,连续反应１５０ｍｉｎ后其反应活性不降低,且未观察到ＣＯ或ＣＯ２的生成。在９７３Ｋ时ＣＮＴｓ本身可作为ＮＯ分解的催化剂,这是一个非常有意义的结果。     

CO和NO在Rh-V/SiO2上吸附的红外光谱研究

应用原位红外光谱研究了ＣＯ和ＮＯ在还原态Ｒｈ／ＳｉＯ２，Ｒｈ－Ｖ／ＳｉＯ２催化剂上的化学吸附。５７３Ｋ氢还原后，Ｒｈ／ＳｉＯ２上的部分Ｒｈ中心处于Ｒｈ＾０和Ｒｈ＾δ＋（δ≤１）两种状态。加入助剂Ｖ后，Ｒｈ与Ｖ之间发生了某种化学作用，这种作用有利于Ｒｈ金属向钒离子转移电子生成Ｒｈ＾δ＋中心。由ＣＯ和ＮＯ共吸附结果可得：ＮＯ对ＣＯ吸附具有两种影响，一是取代ＣＯ，二是使Ｒｈ＾０中心部分氧化生成Ｒｈ＾δ＋     

Decomposition of no on Pd and Ir. Comparison with Pt and Rh

The unimolecular decomposition of NO has been examine on Pd and Ir and they are compared with the corresponding reactions on Pt and Rh. The runs were carried out in a differential flow reactor, at pressures from 0.01 to 5 Torr and temperatures from 500 to 1800 K. It was found that all rates of product formation could be described by Langmuir-Hinshelwood unimolecular rate expression, with an accuracy of±20% und all conditions. The decomposition of NO was virtually identical on Pt and Pd, and on Rh and Ir, but varied widely with temperature between these two groups of metals.     

Oxidation of NO over cobalt oxide supported on esoporous silica

Cobalt oxide catalysts supported on mesoporous silica (Co3O4/MPS) were prepared, characterized and applied for catalytic oxidation of NO. Effects of catalyst supports, calcination temperatures, H2O and SO2 on NO conversion were investigated. The samples were also characterized by BET, XRD, FTIR and TG/DTG. The results suggested that Co3O4/MPS catalyst calcined at 573 K had the smallest crystal particles and the best surface dispersion. This catalyst had the highest activity and yielded 82% NO conversion at 573 K, at a space velocity of 12000 h−1. Although the conversion of NO decreased with the introduction of H2O, it could be restored completely after removing residual H2O from Co3O4/MPS catalyst by heating at 573 K. In the presence of SO2, the oxidation activity decreased and CoSO4 was detected on the catalyst. The NO conversion decreased to 30.2% in the presence of SO2 and H2O. It could not be restored completely after cutting off H2O and SO2. The deactivation of the catalyst in the presence of SO2 and H2O was attributed to the formation of cobalt sulfate species.     

N2 emission in NO and N2O reduction on Rh(100) and Rh(110)

The angular distribution of desorbing N(2) was studied in both the thermal decomposition of N(2)O(a) on Rh(100) at 60-140 K and the steady-state NO (or N(2)O) + D(2) reaction on Rh(100) and Rh(110) at 280-900 K. In the former, N(2) desorption shows two peaks at around 85 and 110 K. At low N(2)O coverage, the desorption at 85 K collimates at about 66 degrees off normal towards the [001] direction, whereas at high coverage, it sharply collimates along the surface normal. In the NO reduction on Rh(100), the N(2) desorption preferentially collimates at around 71 degrees off normal towards the [001] direction below about 700 K, whereas it collimates predominantly along the surface normal at higher temperatures. At lower temperatures, the surface nitrogen removal in the NO reduction is due to the process of NO(a) + N(a) --> N(2)O(a) --> N(2)(g) + O(a). On the other hand, in the steady-state N(2)O + D(2) reaction on Rh(110), the N(2) desorption collimates closely along the [001] direction (close to the surface parallel) below 340 K and shifts to ca. 65 degrees off normal at higher temperatures. In the reduction with CO, the N(2) desorption collimates along around 65 degrees off normal towards the [001] direction above 520 K, and shifts to 45 degrees at 445 K with decreasing surface temperature. It is proposed that N(2)O is oriented along the [001] direction on both surfaces before dissociation and the emitted N(2) is not scattered by adsorbed hydrogen.     

The origin of the decline in the photocatalytic activity of TiO<Subscript>2</Subscript> in the decomposition of NO: TPD spectra of the adsorbed NO species

In order to investigate the cause of the decline in the photocatalytic activity of TiO₂ in the decomposition of NO in a flow reaction system, detailed TPD measurements of the photocatalysts were carried out after the photoreactions. It was found that the TPD peak assigned to the adsorbed NO species observed at around 524 K is directly associated with a decline in the photocatalytic activity. The TPD spectrum of the adsorbed NO species consisted of three different types of species. The -adsorbed species of NO, formed under UV irradiation on the active surface sites, was found to cause a remarkable decline in the photocatalytic activity of TiO₂. It was also found that this decline could be recovered to its original activity by heat treatment with Ar and/or O₂ at around 573 K.     

煤炭解耦燃烧过程N迁移与转化Ⅱ:单组分气相化学反应实验

在理想平推流反应器中进行了模拟热解气对模拟烟气中NO、N₂O的还原实验研究,考察了反应温度、过剩空气系数λ、热解气中CH₄、CO、H₂、NH₃浓度、烟气中NO、N₂O浓度变化对NO、N₂O出口浓度的影响。实验结果表明,当模拟热解气仅含其中一种气体时,在反应温度973~1 223 K时热解气中CH₄、CO、H₂基本不与NO发生反应,当λ小于或等于1.0时可降低N₂O浓度0%~30%;热解气中NH₃可降低NO 10%~60%,但NH₃不与N₂O发生反应。     

SiO2—Al2O3和MgO催化剂上吸附CH3NO2的TPD和IR研究

用TPD和IR方法研究了CH_3NO_2在典型固体酸SiO_2-Al_2O_3和固体碱MgO催化剂上的吸附分解。结果表明,在SiO_2-Al_2O_3表面CH_3NO_2吸附转化为表面甲酰胺物种,后者在高温下分解为CO_2和NH_3。在MgO表面CH_3NO_2吸附形成多种表面化学物种,它们在升温过程中脱附,并通过表面亚硝基甲烷物种分解为NO、C_2H_4、C_2H_6和N_2O.讨论了CH_3NO_2分解过程中表面酸、碱中心的作用。     

Structural characterization and electrochemical lithium insertion properties of carbon nanotubes prepared by the catalytic decomposition of methane

Carbon nanotubes (CNTs) were synthesized by the catalytic decomposition of methane at 773, 873 and 973 K. Structures of these carbon nanotubes were characterized by TEM, HRTEM, XRD and Raman spectra, respectively. The results showed that with the increase of preparation temperature, the d ₀₀₂ value of the CNTs decreased, while the L _a values and the degree of crystallinity of the samples increased. Electrochemical lithium insertion properties of the CNTs used as positive electrodes in CNTs/Li cells were also investigated. The first charge capacities of CNTs/Li cells were 290, 254 and 202 mAh/g for samples produced at 773, 873 and 973 K, respectively. The sample from 773 K showed a larger charge capacity, which is attributed to the accommodation of lithium at microcavities, at edges of graphitic layers and at the surface of single graphitic layers. Its potential hysteresis during Li insertion and deinsertion processes may be related to the interstitial carbon atoms. Electronic Publication     

Templated synthesis and catalytic properties of an Rh/ceria-zirconia catalyst

Ceria-zirconia nanophase with structural defects and high thermal stability was synthesized by a surfactant-templated method. The 0.5 wt.% Rh/ceria-zirconia catalyst shows high activity for NO reduction by CO under an oxygen-rich condition, and the selectivity to 100% N₂ below 200°C was achieved.     

煤炭解耦燃烧过程N迁移与转化Ⅲ:多组分气相化学反应实验

在理想平推流反应器中进行了模拟热解气对模拟烟气中NO、N₂O的还原实验研究,考察了反应温度、过剩空气系数,模拟热解气中CH₄、CO、H₂、NH₃入口浓度与模拟烟气中NO、N₂O入口浓度对NO、N₂O与总氮转化率的影响。结果表明,向NH₃添加可燃气体CO、H₂、CH₄可使NO还原窗口向低温方向移动150~200 K,该温度窗口为1 073~1 223 K;但NH₃-CO-H₂-CH₄-O₂体系对NO、N₂O的还原分解作用依赖于体系的O₂浓度,仅在富燃料情形(过剩空气系数λ为0.6)下可分别达60.6%、100%的NO、N₂O脱除率;在反应温度1 073~1 223 K及过剩空气系数λ为0.6条件下,较高的热解气CH₄、CO、H₂浓度可增加NO排放,但有利于还原N₂O;增加NH₃入口浓度可增加NO分解率。     

NO在Rh(100),Rh(111)面上吸附与直接分解的密度泛函理论研究

本文应用第一性原理的密度泛函(DFT)方法,使用DMol³计算程序,对NO在Rh(100)和Rh(111)面上的吸附与分解进行量化计算,力图解决NO在Rh(100)和Rh(111)面上的优选吸附位、直接分解的过渡态和活化能等重要问题.     

Mo助剂对Rh／SiO_2催化剂上甲醇吸附性能的影响

用原位红外光谱和程序升温还原技术考察了甲醇在Ｒｈ－Ｍｏ／ＳｉＯ入催化剂上的吸附和还原性能．红外结果表明，甲醇在ＳｉＯ２上主要以分子形式吸附．Ｒｈ／ＳｉＯ２和Ｒｈ－Ｍｏ／ＳｉＯ２在室温下对甲醇分解就有活性，分解生成的ＣＯ以线式和桥式吸附态存在．在５７３Ｋ下用甲醇处理后，Ｒｈ／ＳｉＯ２上ＣＯ线式和桥式谱带分别位于２０５０和１９０７ｃｍ－１，而Ｒｈ－Ｍｏ（１：１）／ＳｉＯ２上线式ＣＯ位于２０３６ｃｍ－１，桥式ＣＯ强度很弱．Ｍｏ的添加有可能覆盖部分Ｒｈ金属表面的吸附中心，从而降低ＣＯ吸附谱带的强度，同时使桥式ＣＯ的形成变得困难．随Ｍｏ助剂量的增加，Ｒｈ的还原温度升高，而Ｍｏ的还原温度降低．由此推断，Ｒｈ～Ｍｏ／ＳｉＯ２催化剂上的Ｒｈ可能有三种存在形式：氯化物、低温还原氧化物和高温还原氧化物．     

催化裂解CH4制备碳纳米管的影响因素

以柠檬酸法制备的Fe-MgO、Co-MgO和Ni-MgO为催化剂,CH4为碳源气,H2为还原气,在873、973和1073 K制备出碳纳米管,通过TEM和拉曼光谱表征,讨论了催化剂、制备温度、反应时间等因素对碳纳米管形貌、产率和内部结构的影响.结果表明:不同的催化剂在相同的温度下制备的碳纳米管的形态和内部结构有很大的差异.其中Fe-MgO催化剂制备的碳纳米管管径粗,且大小不均匀,而Ni-MgO催化剂制备的碳纳米管管径较细、较均匀.碳纳米管的产率随着裂解温度的变化而改变.Fe-MgO催化剂制备碳纳米管的产率随制备温度的升高而提高,而Ni-MgO催化剂制备碳纳米管的产率随制备温度的升高而降低.Fe-MgO催化剂制备碳纳米管,在1073K甚至更高的制备温度才能达到其最高产率.Co-MgO催化剂制备碳纳米管的产率在973 K左右产率较高,而用Ni-MgO催化剂制备碳纳米管,则在873 K甚至更低的制备温度就能达到最高产率.反应时间与碳纳米管的产率不成正比,有一最佳反应时间,如Ni-MgO催化剂的最佳反应时间为2 h.     

乙酸在SmOx/Rh(100)模型表面上的吸附和分解

 用高分辨电子能量损失谱（HREELS）和热脱附谱（TDS）研究了\r\n乙酸在SmOx／Rh（100）模型表面上的吸附与分解．结果表明：低温下\r\n吸附乙酸时，SmOx的加入明显促进了乙酸分子中O－H键的断裂，从而有\r\n利于乙酸根的形成；升高表面温度，SmOx的存在促进了乙酸根中C－C键\r\n的断裂，有利于乙酸根的进一步分解．120K时，乙酸在SmOx／Rh（100\r\n）上主要以乙酸根的形式存在．225K时，乙酸根即可发生以生成CO为主\r\n的脱羧反应．在417和477K观察到受表面脱羧反应控制的CO2和H2的脱附\r\n峰．对反应的机理进行了讨论．     

微量铂掺杂对TiO2粉末结构和性能的影响

采用溶胶-凝胶法制备了铂掺杂的TiO2粉末, 利用透射电子显微镜、X射线光电子能谱、紫外可见光谱和X射线衍射技术对粉末的结构和光吸收性能进行了表征. 结果表明, Pt/TiO2粉末主要含有Ti, O, Pt和C元素, 其中Pt主要以0价态存在. 573～873 K焙烧的Pt/TiO2粉末中, TiO2是锐钛矿结构, 973 K焙烧时, 有6.3%的TiO2转变为金红石结构. Pt/TiO2粉末的晶粒尺寸小, 铂和锐钛矿结构TiO2粒子都是纳米颗粒. 随焙烧温度升高, 粉末中TiO2的晶粒尺寸逐渐增大, 晶格常数a和c发生各向异性的变化, 单胞体积在相变时发生收缩. 与TiO2粉末相比, Pt/TiO2粉末中两种结构TiO2的晶格常数和晶胞体积基本上都增大了, 光谱吸收范围被明显拓展至可见光, 实现了可见光催化的基础.     

CO和NO在Rh2-V/SiO2催化剂上共吸附的红外光谱

应用CO和NO吸附态原位红外光谱方法研究了还原态Rh2／SiO2，Rh2－V／SiO2催化剂上的活性中心铑的状态和助剂钒的作用. Rh2催化剂用Rh2（CO）4Cl2化合物制备. 在还原Rh2／SiO2催化剂上，CO吸附出现四个红外吸收峰：2085，2028cm－1（孪生态吸附RhⅠ（CO）2），2060cm－1（线式吸附RhⅡCO），1867cm－1（桥式吸附RhⅢ2CO）．在还原Rh2－V／SiO2催化剂上，CO在RhⅡ和RhⅢ中心上的吸附峰大大减弱，可以解释为Rh°向钒离子转移电子生成了带正电荷的铑中心（Rhδ＋）；同时RhⅠ（CO）2键能增加，降低了孪生CO被NO置换的程度。     

乙醇在Mn薄膜／Rh（100）上吸附和分解的研究

应用高分辨电子能量损失谱（HREELS）和热脱附谱（TDS）,研究了Mn薄膜／Rh(100)上乙醇的吸附和分解,提出了表面吸附和分解的反应工,在300K时,蒸镀的Mn在清洁Rh(100)表面上以层层模式生长;在130－300K间,在25mLMn/Rh(100)表面上吸附20L乙醇的TDS结果与乙醇在Rh(100)表面上的结果一致在155K处,脱附出多层凝聚态吸附的乙醇;升温到255K,脱附出H2和CH4,继续升温,出现了与乙醇在R (100)表面上不一致的现象,在470K,同时出现了第2个H2和CH4的脱附峰,在500K,脱附极少量的CO;在950K附近,脱附出大量CO。     

蒸汽活化生物质焦吸附模拟烟气中SO2和NO的研究

以麦秆和稻壳生物质为研究对象,在不同的热解温度、热解速率以及蒸汽活化温度条件下制备了生物质焦,采用比表面积与孔隙度分析仪测定生物质焦的比表面积和孔隙结构参数。利用固定床吸附装置,研究了热解温度、热解速率、活化温度和模拟烟气中SO₂和NO浓度等因素对生物质焦吸附SO₂和NO性能的影响。结果表明,蒸汽活化可以显著提高生物质焦的BET比表面积、D-R比表面积、D-R微孔容积和总孔容,降低其平均孔径,并显著增加蒸汽活化生物质焦对SO₂与NO吸附的起始穿透时间和吸附量。快速热解下制得的蒸汽活化焦对SO₂和NO的吸附效果优于慢速热解,热解温度为873 K的蒸汽活化焦的吸附性能明显好于热解温度为673与1 073 K的蒸汽活化焦。在973~1 173 K下,随着蒸汽活化温度的提高,蒸汽活化生物质焦对SO₂和NO的吸附量呈现先上升后下降的趋势。随着模拟烟气中SO₂与NO浓度的降低,蒸汽活化生物质焦对SO₂与NO吸附的起始穿透时间延长,但相应的SO₂和NO吸附量下降。在873 K、快速热解和1 073 K条件下制得的蒸汽活化麦秆焦对SO₂和NO吸附量最大,其值分别为109.02和21.77 mg/g。     

ZrO2在Rh/γ-Al2O3催化剂中对NO催化还原反应的作用

测定了含ZrO2的Rh/γ-Al2O3催化剂上NO+C2H4和NO+C2H4+O2的反应活性,并应用TPR、XRD、BET比表面等表征了ZrO2的加入方式和晶型对Rh/γ-Al2O3催化剂活性和结构的影响。结果表明,ZrO2的加入一定程度地抑制了Rh3+与γ-Al2O3之间的相互作用和γ-Al2O3的相变,提高了催化剂的热稳定性,明显提高了850℃老化样品的NO+C2H4反应活性。对于NO+C2H4+O2反应,含ZrO2样品的选择还原活性却较低,表明反应机理不同,而且ZrO2对C2H4的深度氧化有促进作用,但老化后活性下降幅度比不含ZrO2的样品小。