CuPd催化剂调节中间反应能垒提高电催化CO2生成二碳产物的选择性

过度的碳排放已造成了严重的全球环境问题,电催化CO2还原是一种利用间歇性过剩电能将CO2转化为有价值的化学物质的有效策略.在多种CO2还原产物中,二碳(C2)产物(如乙烯、乙醇)因其比一碳产物(如甲酸、甲烷、甲醇)具有更高的能量密度而备受关注.Cu是唯一能用电化学方法将CO2转化为多碳产物的单金属催化剂.如何提高Cu基催化剂上CO2还原为C2产物的效率已引起了极大关注.电催化还原CO2生成C2产物有两个重要步骤:一是参与碳碳偶联反应的CO*中间体的量(*代表中间体吸附在基底表面),二是碳碳偶联步骤的能垒.对于Cu单金属催化剂,虽然其表面碳碳偶联步骤的能垒相对较低,但是Cu对CO2的吸附能力和CO2*加氢能力并不高,导致在Cu表面不能生成足量的CO*中间体参与碳碳偶联反应,因而对C2产物的选择性和活性并不理想.与Cu单金属催化剂相反,在Pd单金属催化剂表面,CO*中间体的形成具有超快的反应动力学,但是CO*易在Pd表面中毒且后续碳碳偶联步骤的能垒极高,使其表面不能生成C2产物.为了充分发挥Cu(碳碳偶联步骤能垒较低)和Pd(CO*形成具有超快反应动力学)的双重优势,本文构建了一种紧密的CuPd(100)界面,以调节中间反应能垒,从而提高C2产率.密度泛函理论(DFT)计算表明,CuPd(100)界面增强了CO2的吸附,且降低了CO2*加氢步骤的能垒,从而能够催化生成更多的CO*中间体参与碳碳偶联反应.且CuPd(100)界面上CO2还原为C2产物的电位决定步骤能垒为0.61 eV,低于Cu(100)表面的(0.72 eV).本文采用了一种简便的湿化学法制备了CuPd(100)界面催化剂.X射线衍射和X射线光电子能谱测试以及扩展X射线吸收精细结构光谱结果表明,合成的是相分离的CuPd双金属催化剂,而非CuPd合金催化剂.同时高分辨透射电镜可以观察到清晰的CuPd(100)界面.由此可见,本文成功合成了CuPd(100)界面催化剂.程序升温脱附实验结果表明,CuPd(100)界面对CO2和CO*的吸附比Cu强,结果与理论预测一致.气体传感实验结果表明,CuPd(100)界面CO2*加氢能力比Cu强.为评估CuPd(100)界面催化剂的催化活性,进行了CO2电化学还原实验.结果表明,在0.1 mol/L的KHCO3电解液中,CuPd(100)界面催化剂在–1.4 VRHE下,C2产物的法拉第效率为50.3％ ±1.2％,是同电位下Cu催化剂的(23.6％ ±1.5％)的2.1倍,C2产物的选择性是Cu催化剂的2.4倍,且具有更高的电流密度和更大的电化学活性面积.本文通过调控中间反应能垒以合理设计铜基CO2还原电催化剂提供了参考.     

ZnO或K_2O助剂对Cu/SiO_2-Al_2O_3催化剂上丙三醇和苯胺气相催化合成3-甲基吲哚反应的促进作用

研究了ZnO或K2O助剂对Cu/SiO2-Al2O3上丙三醇和苯胺气相催化合成3-甲基吲哚反应的促进作用,采用X射线衍射、透射电子显微镜、H2程序升温还原、NH3程序升温脱附以及热重-差热分析等技术对催化剂进行了表征.结果表明,适量ZnO或K2O的加入可明显提高催化剂的活性、选择性和稳定性,其中以ZnO的促进作用更强.ZnO不仅能增强活性组分Cu与SiO2-Al2O3载体之间的相互作用、提高Cu在载体表面的分散度,而且可有效抑制反应过程中Cu粒子的烧结;而K2O的加入却降低了Cu分散度,但也对反应过程中Cu粒子的烧结有所抑制.ZnO或K2O的加入均不同程度地增加了Cu/SiO2-Al2O3催化剂的弱酸中心数量,从而促进3-甲基吲哚的生成.     

CO_2加氢催化剂Cu/ZrO_2/SiO_2上Zr(IV)表面位对甲醇生成速率的影响（英文）

Cu/ZrO_2/SiO_2是有效的CO_2选择加氢制甲醇催化剂.为了理解混合氧化物基催化剂中ZrO_2的作用,在Cu和Zr的K边进行了原位X-射线吸收光谱测试.在反应条件下, Cu保持金属态,而Zr以三类配位环境的形式存在:体相ZrO_2,配位饱和的、以及不饱和的Zr(Ⅳ)表面位.配位不饱和Zr表面位可通过线性拟合参比的X射线吸收近边结构光谱进行定量,发现其数量与甲醇生成速率有关,因而表明Zr(Ⅳ)Lewis酸表面位在驱动选择生成甲醇反应中的重要性.这与提出的机理是一致的:在裂解H_2的Cu纳米颗粒与稳定反应中间体的Zr(Ⅳ)表面位之间的界面上进行CO_2加氢.     

Cu/Al2O3催化剂的改性及其对NO选择性还原的催化性能

 以 γ-Al2O3 为载体,采用SO2-4进行改性并添加助剂La,再负载上Cu2+, 制备了改性的Cu/Al2O3催化剂(Cu/La/SO2-4/Al2O3),考察了SO2-4改性和助剂La对催化剂在富氧条件下催化丙烯选择性还原NO 反应的影响,并借助红外光谱、X射线衍射、扫描电镜、热重分析、程序升温还原和X射线光电子能谱等方法研究了改性催化剂的性能与结构的关系. 结果表明,改性催化剂的催化活性较高, NO转化率可高达83.7%. 采用SO2-4改性可促进催化剂表面的酸量增加,并促使产生B酸中心; 助剂La可提高Cu物种的分散程度,并提高催化剂的热稳定性和还原性,从而可有效提高催化剂在富氧条件下对丙烯选择性还原NO反应的催化活性和水热稳定性.     

K促进的纳米片状水滑石衍生CoAlO金属氧化物催化碳烟燃烧

采用水热法合成了负载K的纳米片状水滑石衍生CoAlO金属氧化物,其表现出优异的催化碳烟燃烧活性.氢气-程序升温还原（H₂-TPR）实验结果表明,K与Co之间的相互作用提高了催化剂的氧化还原性能.X射线光电子能谱（XPS）分析结果表明,K的负载增大了表面Co²⁺/Co³⁺的比例,促进了氧空位的产生,提高了催化剂对气相氧的吸附能力.碳烟-程序升温还原（Soot-TPR）实验结果表明,K的负载增加了表面吸附氧数量.动力学实验结果表明,K的负载增加了单位质量催化剂上的活性氧数量、反应速率和转化频率（TOF）,从而提高了催化剂的本征活性.另外,碳烟颗粒可以分散在纳米片的层间,与活性位点的接触效率得到提高,也有利于提高催化碳烟燃烧活性.     

K和Cu部分取代对LaMnO3钙钛矿型催化剂同时去除Nox和碳烟的影响

 用K部分取代LaMnO3中的La得到La0.8K0.2MnO3, 再用Cu部分取代Mn得到La0.8K0.2CuxMn1-xO3, 采用程序升温反应方法对催化剂同时去除NOx和碳烟的性能进行评价,然后利用XPS从分子水平来解释部分取代对LaMnO3钙钛矿催化剂性能的影响. 结果表明,两种不同取代更有利于催化剂形成钙钛矿型晶体结构,为了保持分子的电中性, K部分取代使得Mn2+转变成Mn3+, 部分转变成Mn4+, 从而使催化剂的活性及选择性大幅度提高. Cu部分取代进一步使部分Mn3+转变成Mn4+, 催化剂的活性有所降低,但由于Cu2+和Mn3+的协同作用,催化剂的选择性得到进一步的提高. 对于同时催化去除NOx和碳烟反应,催化剂中起决定性作用的是表面的Mn3+和Cu2+.     

碱金属助剂对 Au-Pt/CeO2 催化剂催化水煤气变换反应活性的影响

 制备了碱金属 M (M = Na, K, Rb 和 Cs) 掺杂的 Au-Pt/CeO2 催化剂, 考察了其催化水煤气变换反应的活性, 并采用 X 射线衍射、H2 程序升温还原、紫外-可见漫反射光谱和 X 射线光电子能谱技术研究了 K 助剂对 Au-Pt/CeO2 催化剂结构和表面性质的影响. 结果表明, 添加少量电负性较低的 K 虽然使 Pt 的还原变得困难, 但有利于 Au 金属态的稳定, 并使催化剂表面 Ce3+ 富集而产生氧空位, 显著提高了 Au-Pt/CeO2 催化剂活性. 当 K 负载量为 0.025%, 反应温度 250 oC 时, CO 转化率可达 95%.     

CO2对浆态床一步法合成二甲醚铜基催化剂稳定性的影响

研究了260℃,5.0MPa和原料气空速4000h-1条件下,不同浓度的CO2对甲醇合成Cu基催化剂稳定性的影响.结果表明,原料气中较高浓度的CO2可导致Cu基甲醇合成催化剂快速失活.原料气中CO2浓度的增大可促进逆水煤气变换反应,导致反应体系中H2O的量增加,不能被及时导出反应体系的H2O使Cu基催化剂的晶体结构和表面特性发生了变化.采用程序升温还原、N2吸附、元素分析、透射电镜和X射线光电子能谱分别对较低浓度和较高浓度CO2反应条件下的催化剂进行了表征.结果表明,原料气中较高浓度的CO2可导致催化剂颗粒变大,孔径减小,比表面积降低,催化剂中元素Zn和Al有明显的流失,Cu与ZnO之间的协同作用有所减弱,这些都是导致催化剂失活的重要原因.原料气中较高浓度的CO2在一定程度上抑制了催化剂上积炭的生成.     

CuCl_2和HY分子筛的表面反应及Cu/Y分子筛的制备及其催化甲醇氧化羰基化（英文）

以CuCl2为前驱物与HY分子筛进行固相离子交换制备了Cu/Y催化剂,采用热重方法研究了CuCl2与HY分子筛的表面固相离子交换反应,结合活性测试表明催化剂中高度分散的CuCl和离子交换形式的Cu+物种是甲醇氧化羰基化合成碳酸二甲酯的催化活性中心.X射线光电子能谱表征和元素分析结果表明,活性金属Cu主要以CuCl形式存在于分子筛外表面,而在分子筛笼内则以交换的Cu+和少量吸附的CuCl形式存在.与以CuCl为交换铜源所制催化剂相比,以CuCl2为铜源制备的催化剂Cu含量低,催化活性更高.     

双金属NiCu/MgO催化剂上葡萄糖氢解制备高附加值C2-C4化学品（英文）

采用共沉淀法制备了不同Ni/Cu比的NiCu/MgO双金属催化剂,并通过N_2物理吸附、X射线衍射(XRD)、X射线光电子能谱(XPS)和程序升温还原等方法对NiCu/MgO催化剂结构进行表征.表征结果表明,Cu和Ni之间存在协同相互作用,NiMgO_2的存在抑制了镍物种的还原和Cu-Ni合金的形成,催化剂的Ni/Cu比和焙烧温度对其表面金属组成有非常重要的影响.以葡萄糖氢解反应为探针反应,考察了Ni/Cu比、焙烧温度、H_2压力、反应温度、反应时间等因素对NiCu/MgO催化性能的影响.研究表明相对于单金属催化剂,双金属催化剂对葡萄糖氢解生成C2-C4和1,2-PD具有较高的催化活性,这与铜镍之间的协同作用有关.     

Effect of surface structure on the catalytic behavior of Ni：Cu/Al and Ni：Cu：K/Al catalysts for methane decomposition

Methane decomposition using nickel, copper, and aluminum （Ni：Cu/Al） and nickel, copper, potassium, and aluminum （Ni：Cu：K/Al） modified nano catalysts has been investigated for carbon fibers, hydrogen and hydrocarbon production. X-ray photoelectron spectroscopy （XPS）, static secondary ion mass spectrometry （SSIMS）, thermal gravimetric analysis （TGA）, Fourier transform infrared （FT-IR）, secondary electron microscopy/X-ray energy dispersive （SEM-EDX）, and temperature programmed desorption （TPD） were used to depict the chemistry of the catalytic results. These techniques revealed the changes in surface morphology and structure of Ni, Cu, Al, and K, and formation of bimetallic and trimetallic surface cationic sites with different cationic species, which resulted in the production of graphitic form of pure carbon on Ni：Cu/Al catalyst. The addition of K has a marked effect on the product selectivity and reactivity of the catalyst system. K addition restricts the formation of carbon on the surface and increases the production of hydrogen and C2, C3 hydrocarbons during the catalytic reaction whereas no hydrocarbons are produced on the sample without K. This study completely maps the modified surface structure and its relationship with the catalytic behavior of both systems. The process provides a flexible route for the production of carbon fibers and hydrogen on Ni：Cu/Al catalyst and hydrogen along with hydrocarbons on Ni：Cu：K/Al catalyst. The produced carbon fibers are imaged using a transmission electron microscope （TEM） for diameter size and wall structure determination. Hydrogen produced is COx free, which can be used directly in the fuel cell system. The effect of the addition of Cu and its transformation and interaction with Ni and K is responsible for the production of CO/CO2 free hydrogen, thus producing an environmental friendly clean energy.     

Role of stress in the self-limiting oxidation of copper nanoparticles

The oxidation process of Cu nanoparticles has been investigated by means of an in-situ X-ray diffraction method. A self-limiting oxidation process involving an unusually drastic decrease (about 4 orders in magnitude) in the oxidation rate was observed at 298 K, whereas a non-self-limiting oxidation emerged at 323 K with a rate of at least 4 orders in magnitude faster than 298 K. The drastic slowing at 298 K and the big differences between the two close temperatures in the oxidation kinetics were found to be directly correlated to whether the compressive stress in the Cu(2)O(111) layers that commensurately formed on the Cu(111) surface is relaxed or not.     

Chemical interactions in the layered system BC x N y /Ni(Cu)/Si, produced by CVD at high temperature

Layered samples Si(100)/C/Ni/BC(x)N(y) and Si(100)/C/Cu/BC(x)N(y) were produced by physical vapor deposition of a metal (Ni, Cu, resp.) and low-pressure chemical vapor deposition of the boron carbonitride on a Si(100) substrate. Between the Si and the Ni (Cu) and on the surface of the Ni (Cu) layer, thin carbon layers were deposited, as a diffusion barrier or as a protection against oxidation, respectively. Afterwards, the surface carbon layer was removed. As precursor, trimethylamine borane and, as an auxiliary gas, H(2) and NH(3) were used, respectively. The chemical compositions of the layers and of the interfaces in between were characterized by total-reflection X-ray fluorescence spectrometry combined with near-edge X-ray absorption fine-structure spectroscopy, X-ray photoelectron spectroscopy, and secondary ion mass spectrometry. The application of H(2) yielded the BC(x)N(y) compound whereas the use of NH(3) led to a mixture of h-BN and graphitic carbon. At the BC(x)N(y)/metal interface, metal borides could be identified. At the relatively high synthesis temperature of 700 °C, broad regions of Cu or Ni and Si were observed between the metal layer and the substrate Si.     

预处理条件对用于CO_2加氢的超细CuO－ZnO－SiO_2催化剂性能的影响

采用ＸＲＤ、ＢＥＴ、ＴＰＲ手段，研究了焙烧和还原温度对超细ＣｕＯ－ＺｎＯ－ＳｉＯ２催化剂的性质及其ＣＯ２加氢反应催化活性的影响．胶体在５７３－７７３Ｋ范围内焙烧生成ＣｕＯ、Ｃｕ２Ｏ、ＺｎＯ晶相，随着焙烧温度继续升高，ＣｕＯ和ＺｎＯ晶粒逐渐变大，但催化剂的比表面积和孔容变化很小．在９７３Ｋ焙烧后出现Ｚｎ２ＳｉＯ４晶相，使催化剂比表积和孔容变小，导致催化剂活性降低．焙烧温度对催化剂活性的影响大于对ＣＯ２加氢产物分布的影响．在５４８－６４８Ｋ范围内，催化剂还原温度对其催化活性影响不大．７０３Ｋ高温还原后，可能由于Ｃｕ０晶粒的出现，使得催化剂的活性下降．ＴＰＲ研究结果进一步表明，焙烧温度影响ＣｕＯ同ＺｎＯ、ＳｉＯ２之间的相互作用和催化剂的还原行为．     

XPS and ISS analysis of Fischer-Tropsch catalysts

Summary The surface compositions of K and Cu containing Fe/Mn oxide catalysts for Fischer-Tropsch synthesis were investigated by XPS and ISS. The surface species after calcination are identified as Fe₂O₃, Mn₂O₃, MnO₂, CuO and most likely KO₂, and after in situ reduction at 723 K Fe⁰, Cu⁰, Fe²⁺ and Fe³⁺ oxides, MnO and KOH. Mn and K are enriched on the surfaces after calcination and reduction; the Cu surface content is approximately equal to the bulk concentration. The K enrichment is especially strong and ISS indicates that potassium is mainly confined to the uppermost layers. The degree of reduction of Fe is strongly dependent on the amount of Cu or K. The change in surface composition during Fischer-Tropsch reaction in the XPS equipment can be correlated to the activity of the catalysts. The pure and Cu containing samples show a constant activity and only a small increase in carbon surface concentration. The K containing catalysts deactivate after a short time and are then totally covered by carbon. On all catalyst surfaces a small amount of carbonate is formed.

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XPS- and ISS-Analyse von Fischer-Tropsch-Katalysatoren

     

Investigation of the crystal structure and the structural and magnetic properties of SrCu2(PO4)2

SrCu2(PO4)2 was prepared by the solid-state method at 1153 K. Its structure was solved by direct methods in the space group Pccn (No. 56) with Z = 8 from synchrotron X-ray powder diffraction data measured at room temperature. Structure parameters were then refined by the Rietveld method to obtain the lattice parameters, a = 7.94217(8) A, b = 15.36918(14) A, and c = 10.37036(10) A. SrCu2(PO4)2 presents a new structure type and is built up from Sr2O16 and Cu1Cu2O8 units with Cu1...Cu2 = 3.256 A. The magnetic properties of SrCu2(PO4)2 were investigated by magnetic susceptibility, magnetization up to 65 T, Cu nuclear quadrupole resonance (NQR), electron-spin resonance, and specific heat measurements. With spin-dimer analysis, it was shown that the two strongest spin-exchange interactions between Cu sites result from the Cu1-O...O-Cu2 and Cu2-O...O-Cu2 super-superexchange paths with Cu1...Cu2 = 5.861 A and Cu2...Cu2 = 5.251 A, and the superexchange associated with the structural dimer Cu1Cu2O8 is negligible. The magnetic susceptibility data were analyzed in terms of a linear four-spin cluster model, Cu1-Cu2-Cu2-Cu1 with -2J(1)/kB = 82.4 K for Cu1-Cu2 and -2J(2)/k(B) = 59 K for Cu2-Cu2. A spin gap deduced from this model (Delta/kB = 63 K) is in agreement with that obtained from the Cu NQR data (Delta/kB = 65 K). A one-half magnetization plateau was observed between approximately 50 and 63 T at 1.3 K. Specific heat data show that SrCu2(PO4)2 does not undergo a long-range magnetic ordering down to 0.45 K. SrCu2(PO4)2 melts incongruently at 1189 K. We also report its vibrational properties studied with Raman spectroscopy.     

Change in carbon content on the surface of a multicomponent catalyst during its reduction, oxidation and due to action of the reaction medium

The change in the carbon content on the surface of Fe, Cu, Ni containing catalysts has been studied by X-ray Photoelectron Spectroscopy (XPS) under different treatments. It has been concluded that the superficial carbon content affects the content of an active element,e.g. copper, on the catalyst surface.     

Interfacial Characteristics and Fracture Toughness of Electrolytically Ni-Plated Carbon Fiber-Reinforced Phenolic Resin Matrix Composites

The electrolytic plating of metallic nickel on a carbon fiber surface has been carried out in order to improve the interfacial adhesion and the mechanical properties in carbon fiber/phenolic matrix composite systems. The surface and the mechanical interfacial properties of composites are characterized by X-ray photoelectron spectrometry (XPS), surface free energy, and the critical stress intensity factor (K(IC)). From the experimental results, it is clearly revealed that the oxygen functional groups and the metallic nickel on fibers largely affect the mechanical interfacial behavior of the composites, resulting in increased surface polarity, whereas the nitrogen functional groups have no effect. Also, a good correlation between surface oxygen functional groups and mechanical interfacial properties and between wettability and K(IC) is established and it is found that a 10 A m(-2) current density is the optimum condition for this system. Copyright 2001 Academic Press.     

Study of activated carbon supported iron catalysts for the Fischer-Tropsch synthesis

Summary Characterization (BET and TPD) and reaction studies were conducted with activated carbon supported iron catalysts (Fe/AC) used for the Fischer-Tropsch synthesis (FTS). The TPD study showed that there existed interactions between metals and the AC surface. Greater association of Cu and K promoters with the AC surface resulted in stronger promoter to surface interaction, which enhanced the H₂ desorption ability of the Cu and K promoted Fe/AC catalyst prepared under vacuum impregnation (VI). Catalytic behavior of a Fe/AC catalyst (VI-15 Fe/2 Cu/2 K/81 AC, in parts per weight) was studied in a 1-liter slurry phase continuous stirred tank reactor. The catalyst presented moderate syngas conversion (44.3-60.6%) and high gaseous selectivity (CH₄, 12.8-15.1% and C₂-C₄, 42.4-46.1%) under 304^oC, 3.0 MPa, 1.1 L(STP)/g-cat/h, and H₂/CO = 2.0 during 166 h of testing. Detectable hydrocarbons up to C₁₈ were formed on the Fe/AC catalyst.     

Carbon-nitrogen place exchange on NO exposed beta-Mo2C

Atomic nitrogen and oxygen were deposited on beta-Mo(2)C through dissociative adsorption of NO. Reflectance absorbance infrared spectroscopy (RAIRS), thermal desorption, and synchrotron X-ray photoelectron spectroscopy (XPS) measurements were used to investigate the interplay between atomic nitrogen, carbon, and oxygen in the 400-1250 K region. The combination of the high resolution and high surface sensitivity offered by the synchrotron XPS technique was used to show that atomic nitrogen displaces interstitial carbon onto the carbide surface. Thermal desorption measurements show that the burnoff of the displaced carbon occurs at approximately 890 K. The incorporation of nitrogen into interstitial sites inhibits oxygen dissolution into the bulk. RAIRS spectroscopy was used to identify surface oxo, terminal oxygen, species formed from O(2) and NO on beta-Mo(2)C.