铂基团簇Pt3X(X=Al，Si，Cu)催化水制氢及其水解副产物氧化CO

本文基于第一性原理研究了利用具有幻数结构特点的Pt₃X(X=Al，Si，Cu)团簇仅通过一步反应就能催化分解水制氢的反应过程. 吸附物H₂O@Pt₃X团簇在波长300∽760 nm的紫外和可见光范围内有强吸收，表明太阳光可以方便地用于Pt₃X的催化水解制氢的反应. 此外，水解后滞留在团簇上的O原子可在反应活化能为0.34∽0.58 eV内与CO氧化反应生成CO₂. 这个通过氧化消除“毒性”CO的结果表明了反应副产物有能作催化剂的循环再利用能力. 本文发现生成的CO₂分子还可以在323 K的温度下脱离Pt₃X小团簇.     

使用金属掺杂SnO2(110)作为表面催化剂的电催化CO2还原反应：通过调控Sn:O原子比例来控制产物

电催化CO₂还原反应可以产生HCOOH和CO,目前该反应是将可再生电力转化为化学能存储在燃料中的最有前景的方法之一. SnO₂作为将CO₂转换为HCOOH和CO的良好催化剂,其反应发生的晶面可以是不同的. 其中(110)面的SnO₂非常稳定,易于合成. 通过改变SnO₂(110)的Sn:O原子比例,得到了两种典型的SnO₂薄膜：完全氧化型(符合化学计量)和部分还原型. 本文研究了不同金属(Fe、Co、Ni、Cu、Ru、Rh、Pd、Ag、Os、Ir、Pt和Au)掺杂的SnO₂(110),发现在CO₂还原反应中这些材料的催化活性和选择性是不同的. 所有这些变化都可以通过调控(110)表面中Sn:O原子的比例来控制. 结果表明,化学计量型和部分还原型Cu/Ag掺杂的SnO₂(110)对CO₂还原反应具有不同的选择性. 具体而言,化学计量型的Cu/Ag掺杂的SnO₂(110)倾向于产生CO(g),而部分还原型的表面倾向于产生HCOOH(g). 此外,本文还考虑了CO₂还原的竞争析氢反应. 其中Ru、Rh、Pd、Os、Ir和Pt掺杂的SnO₂(110)催化剂对析氢反应具有较高的活性,其他催化剂对CO₂还原反应具有良好的催化作用.     

沉淀方法及铈掺杂对铜锰氧化物催化剂催化氧化CO性能的影响

研究了铈掺杂及沉淀方法对铜锰氧化物催化剂的结构特性及室温催化氧化CO性能的影响. 使用X射线衍射、N₂吸附脱附、等离子体发射光谱、程序升温还原、紫外可见漫反射以及X射线光电子能谱等手段对各催化剂进行了表征. 发现掺杂少量的铈于铜锰氧化物催化剂中,CeO₂相高度分散并能阻止催化剂的烧结和团聚,所制得的催化剂的颗粒较小,氧化还原性能提高,比表面增大,并形成了较多的活性位点,使其对CO的催化氧化性能明显提高.     

Cu/HMOR催化二甲醚羰基化合成乙酸甲酯: 催化剂制备方法的影响 (cited: 2)

采用氨蒸发法、尿素水解法、离子交换法及浸渍法制备HMOR负载的Cu催化剂, 考察其催化二甲醚(DME)羰基化合成乙酸甲酯(MA)性能. 结果表明离子交换法制得Cu/HMOR催化剂在Cu的金属中心和酸性分子筛载体的共同作用下具有较好催化反应活性. 在210 oC、1.5 MPa、空速4883 h^-1,DME转化率为95.3%,MA选择性为94.9%. 对催化剂进行N2物理吸附、X射线衍射、NH₃程序升温脱附和CO程序升温脱附等表征发现,离子交换法制得Cu/HMOR催化剂具有较高比表面、大量弱酸及一定中强酸、适中的CO吸附强度,提高了CO插入DME羰基化反应活性.     

无表面活性剂Pt和PtRu纳米粒子制备及其甲醇氧化活性

利用一种简单的方法制备不含任何表面活性剂并具有高甲醇氧化活性的Pt和PtRu纳米电催化剂. 以CO为还原剂, CO和多壁碳纳米管(MWCNT_s)为保护剂和载体,通过一步反应得到沉积在多壁碳纳米管上Pt纳米粒子,在制备过程中无需使用任何有机溶剂或表面活性剂. 利用循环伏安法和计时电流法表征了所合成催化剂的甲醇氧化活性,甲醇氧化的峰电位(ca. 0.9 V vs. RHE)处的电流密度和比质量电流高达11.6 mA/cm² 和860 mA/mg_Pt. 在Pt/MWCNT_s表面电沉积Ru后,催化剂在低电位处的甲醇氧化活性得到提高,其在0.5和0.6 V的稳态比质量电流分别达到了20和80 mA/mg.     

煅烧温度对Cu/HMOR催化剂结构及其催化二甲醚羰基化反应性能影响

采用离子交换法在不同煅烧温度下制备HMOR负载Cu(Cu/HMOR)催化剂,用于催化二甲醚(DME)羰基化合成乙酸甲酯(MA)反应. 活性测试结果表明430 oC煅烧制得Cu/HMOR具有较好催化活性,在210 oC、1.5 MPa、空速4883 h^-1下DME转化率为97.2%,MA选择性为97.9%. 对催化剂进行X射线衍射、N₂物理吸附、NH₃程序升温脱附、CO程序升温脱附及拉曼方法表征. 催化剂经一定的煅烧温度有利于Cu离子迁移及扩散和硝酸铜完全分解,从而使HMOR载体具有较多的酸性活性位、大比表面、适宜的微孔结构以及更多的CO吸附位.     

Cu(221)和CuZn(221)表面甲醇合成的基于第一性原理微观动力学的理论研究

本文基于第一性原理的微观动力学模拟方法,对Cu（221）和CuZn（221）上一氧化碳和二氧化碳加氢到甲醇进行了系统的理论计算研究.研究发现,碳转化率在两个表面上均表现出相同的活性顺序：CO加氢活性 > CO/CO₂混合加氢活性 > CO₂加氢活性.CO的高转化活性源于其基元反应能垒低于CO₂甲醇合成的基元反应能垒.相比于Cu（221）表面,Zn的掺杂显著降低了甲醇合成活性,尤其是CO加氢的活性.对于CO和CO₂共存的情况,研究发现CO是Cu（221）甲醇合成的主要碳源,而CuZn（221）上的碳源则由CO和CO₂共同提供.反应速控度分析表明,CO/CO₂混合气甲醇合成的速控步在Cu（221）表面是HCO、HCOO的加氢,而在CuZn（221）表面速控步则是HCOOH的加氢.这些研究结果表明铜基催化剂上Zn的表面合金效应、以及合成气组分对甲醇合成的活性和反应通道具有重要的影响.     

不同晶相结构和形貌TiO2负载Ru催化剂的CO选择甲烷化

用水热法得到的钛酸纳米纤维前体,通过不同后处理方法合成了多种纳米结构的TiO₂．采用N₂等温吸附和BET比表面、X射线衍射、透射电镜和能量分散X射线分析表征了TiO₂及负载Ru催化剂的微结构,包括比表面、晶相结构和形貌以及Ru纳米颗粒尺寸分布等．对负载Ru催化剂在富氢条件下CO选择甲烷化反应活性测试表明：金红石相TiO₂和TiO₂-B为载体负载的Ru催化剂比锐钛矿相TiO₂负载的Ru催化剂表现出更高的反应性能．其活性区别说明了不同晶相结构和形貌TiO₂载体与Ru纳米颗粒的相互作用存在差异．     

Cu-Zr合金在氢气氛中退火后表面Cu沉积物的光电子能谱研究

对不同成分的Cu-Zr合金,在超高真空(UHV)和在氢气氛中200—400℃退火后的光电子能谱(XPS)研究发现,与多数情况下因氧感应致使Zr发生表面分凝相反,富铜样品在氢气氛下退火,Cu发生强烈的表面分凝;扫描电子显微镜得出表面Cu沉积物的显微照片,显然,这是由于Cu上氢化吸附热的影响所形成。 关键词：     

基于约束非平衡溶剂化理论的对硝基苯胺π-π*光谱移动 (cited: 1)

采用共沉淀法制备不同组分类水滑石前驱体Co-M-Al和Co-M-Ce-Al (M=Zn, Ni, Cu)复合氧化物催化剂催化分解N₂O. 结果表明,Co-M-Al系列氧化物催化剂的催化活性Co-Ni-Al系列>Co-Zn-Al系列>Co-Cu-Al系列;CeO₂添加使得催化剂催化活性进一步提高,N₂O分解温度T₅₀和T₉₀均下降80 oC;继续负载碱金属K也使氧化物催化剂催化活性提高,N₂O分解温度T₅₀和T₉₀下降约50 oC.     

In‐situ Raman spectroscopy study of Ru/TiO2 catalyst in the selective methanation of CO

Raman spectroscopic technique has been used to characterize a Ru/TiO₂ catalyst and to follow in situ their structural changes during the CO selective methanation reaction (S‐MET). For a better comprehension of the catalytic mechanism, the in‐situ Raman study of the catalysts activation (reduction) process, the isolated CO and CO₂ methanation reactions and the effect of the composition of the reactive stream (H₂O and CO₂ presence) have been carried out. Raman spectroscopy evidences that the catalyst is composed by islands of TiO₂–RuO₂ solid solutions, constituting Ru–TiO₂ interphases in the form of Ru_xTi_{1 − x}O₂ rutile type solid solutions. The activation procedure with H₂ at 300 °C promotes the reduction of the RuO₂–TiO₂ islands generating Ru^o–Ti³⁺ centers. The spectroscopic changes are in agreement with the strong increase in chemical reactivity as increasing the carbonaceous intermediates observed. The selective methanation of CO proceeds after their adsorption on these Ru^o–Ti³⁺ active centers and subsequent C―O dissociation throughout the formation of CH_x/C_nH_x/C_nH_xO/CH_x―CO species. These intermediates are transformed into CH₄ by a combination of hydrogenation reactions. The formation of carbonaceous species during the methanation of CO and CO₂ suggests that the CO presence is required to promote the CO₂ methanation. Similar carbonaceous species are detected when the selective CO methanation is carried out with water in the stream. However, the activation of the catalysts occurs at much lower temperatures, and the carbon oxidation is favored by the oxidative effect of water. Copyright © 2015 John Wiley & Sons, Ltd.     

New advanced in situ carbon monoxide sensor for the process application

Mixed potential solid electrolyte CO sensors with sensing electrodes based on composite with various semiconducting oxides were extensively studied in the temperature range 500–650 °C for sensitivity, stability and cross-sensitivity besides CO to other combustion components like CO₂, H₂O, O₂, and SO₂. The highest CO sensitivity was found for the CO sensor with composite electrode based on Au/Ga₂O₃ showing also good reproducibility and stability in hazardous combustion environment. CO sensor response behavior in non equilibrated oxygen containing gas mixtures is mainly determined by the catalytic activity of the measuring electrode and depends strongly on preparation and measuring conditions. Mixed oxides based on doped chromites show only a little sensitivity to CO. CO sensor based on Au/Ga₂O₃ composite electrodes was showing good CO selectivity in the presence of other combustion gas species and finally was tested in combustion environment at power plant. Paper presented at the 11th EuroConference on the Science and Technology of Ionics, Batz-sur-Mer, Sept. 9–15, 2007.     

A versatile sonication-assisted deposition–reduction method for preparing supported metal catalysts for catalytic applications

This work aims to develop a rapid and efficient strategy for preparing supported metal catalysts for catalytic applications. The sonication-assisted reduction–precipitation method was employed to prepare the heterogeneous mono- and bi-metallic catalysts for photocatalytic degradation of methyl orange (MO) and preferential oxidation (PROX) of CO in H₂-rich gas. In general, there are three advantages for the sonication-assisted method as compared with the conventional methods, including high dispersion of metal nanoparticles on the catalyst support, the much higher deposition efficiency (DE) than those of the deposition–precipitation (DP) and co-precipitation (CP) methods, and the very fast preparation, which only lasts 10–20 s for the deposition. In the AuPd/TiO₂ catalysts series, the AuPd(3:1)/TiO₂ catalyst is the most active for MO photocatalytic degradation; while for PROX reaction, Ru/TiO₂, Au–Cu/SBA-15 and Pt/γ-Al₂O₃ catalysts are very active, and the last one showed high stability in the lifetime test. The structural characterization revealed that in the AuPd(3:1)/TiO₂ catalyst, Au–Pd alloy particles were formed and a high percentage of Au atoms was located at the surface. Therefore, this sonication-assisted method is efficient and rapid in the preparation of supported metal catalysts with obvious structural characteristics for various catalytic applications.     

Fuel quality and operational issues for polymer electrolyte membrane (PEM) fuel cells

Polymer electrolyte membrane (PEM) fuel cells are susceptible to degradation due to the catalyst poisoning caused by CO present in the fuel above certain limits. Although the amount of CO in the fuel may be within the permissible limit, the fuel composition (% CO₂, CH₄, CO and H₂O) and the operating conditions of the cell (level of gas humidification, cell temperature and pressure) can be such that the equilibrium CO content inside the cell may exceed the permissible limit leading to a degradation of the fuel cell performance. In this study, 50 cm² active area PEM fuel cells were operated at 55–60 °C for periods up to 250 hours to study the effect of methane, carbon dioxide and water in the hydrogen fuel mix on the cell performance (stability of voltage and power output). Furthermore, the stability of fuel cells was also studied during operation of cells in a cyclic dead end / flow through configuration, both with and without the presence of carbon dioxide in the hydrogen stream. The presence of methane up to 10% in the hydrogen stream showed a negligible degradation in the cell performance. The presence of carbon dioxide in the hydrogen stream even at 1–2% level was found to degrade the cell performance. However, this degradation was found to disappear by bleeding only about 0.2% oxygen into the fuel stream.     

Implication of the role of oxygen anions and oxygen vacancies for methanol decomposition over zirconia supported copper catalysts

The interaction of methanol with Cu, monoclinic ZrO₂, and Cu/m-ZrO₂ catalysts has been investigated by temperature programmed desorption (TPD) and reaction (TPRS) with the aim of understanding the nature of the surface sites and the mechanism involved in methanol decomposition. A synergetic effect has been detected since the combination of copper and ZrO₂ significantly facilitates the methanol decomposition with the facile evolution of H₂ and CO species at much lower desorption temperature. In conjunction with DRIFTS and H₂-TPD measurements of the Cu/ZrO₂ sample reduced at elevated temperatures, methanol decomposition over Cu/ZrO₂ is suggested to occur primarily on ZrO₂ with the aid of the presence of oxygen anions and oxygen vacancies generated by species-spillover between copper and zirconia. The interface between copper and zirconia is also evidenced to be crucial to the decomposition of methanol, with the main role of metallic Cu being to provide sites for H₂ removal by efficiently recombining the hydrogen atoms formed during the dehydrogenation of species located on zirconia.     

Cooperative activation effect on H2O adsorption in MnO–Co catalyzed steam methane reforming

Steam methane reforming is a very important chemical process in hydrogen production and solid oxide fuel cells (SOFCs). Cobalt (Co) is an important catalyst for dry and steam methane reforming. However, previous studies have confirmed that metal Co surfaces only have weak adsorption activity for H₂O, which is evidently unfavorable for steam reforming. In this work we used first-principles simulations to study the activity of MnO–Co catalysts for the adsorption of H₂O. Compared with the Co (111) surface and pristine Co clusters, the MnO–Co catalytic layer has a stronger adsorption capability for H₂O because of the introduction of the MnO substrate, which is crucial for improving the steam reforming reaction and inhibiting carbon disposition in SOFCs. The cooperation mechanism between MnO and Co is discussed based on the analysis of electronic structures. The conclusions from this work are universal for other metal-oxide composite catalyst layers.     

The role of Mössbauer spectrometry in designing a catalyst

In this review some aspects are shown of the role of Mössbauer spectrometry in the understanding and the development of catalysts for the hydrogenation of CO, such as Fe/ZrO₂ for the production of light olefins, Fe/SiO₂ to study the formation of iron pentacarbonyl and Co/Al₂ O₃. Applying this Fischer-Tropsch process fuels of high purity, chemical feedstocks and special chemicals by leading a mixture of CO and H₂ over an iron (cobalt) based catalyst are produced.     

Surface modification of HMS material with silica sol leading to a remarkable enhanced catalytic performance of Cu/SiO2

Cu/SiO₂ catalysts with different bimodal pore structures adjusted by the ratio of HMS and silica sol were prepared via modified impregnation method. Structure evolutions of the catalyst were systematically characterized by N₂-physisorption, X-ray diffraction, H₂ temperature-programmed reduction, N₂O titration and X-ray photoelectron spectroscopy. The results show that the composite silica supported copper catalysts showed remarkably enhanced catalytic performance in the selective hydrogenation of dimethyl oxalate to ethylene glycol compared to the individual silica supported ones obtained by the same method. The dimethyl oxalate conversion and the ethylene glycol selectivity can reach 100% and 98% at 473 K with 2.5 MPa H₂ pressure and 1.5 h⁻¹ liquid hour space velocity of dimethyl oxalate over the optimized Cu/SiO₂ catalyst. The remarkably enhanced catalytic performance of Cu/SiO₂ catalysts might be attributed to the homogeneous dispersion and uniformity of the active copper species and to the larger copper surface areas attained on the HMS supports with large pore diameters and surface areas.     

Atomic O and H exposure of C-covered and oxidized d-metal surfaces

Carbon coverage, oxidation and reduction of Au, Pt, Pd, Rh, Cu, Ru, Ni and Co layers of 1.5 nm thickness on Mo have been characterized with ARPES and desorption spectroscopy upon exposure to thermal H and O radicals. We observe that only part of the carbon species is chemically eroded by atomic H exposure, yielding hydrocarbon desorption. Exposure to atomic O yields complete carbon erosion and CO₂ and H₂O desorption. A dramatic increase in metallic and non-metallic oxide is observed for especially Ni and Co surfaces, while for Au and Cu, the sub-surface Mo layer is much more oxidized. Although volatile oxides exist for some of the d-metals, there is no indication of d-metal erosion. Subsequent atomic H exposure reduces the clean oxides to a metallic state under desorption of H₂O. Due to its adequacy, we propose the atomic oxygen and subsequent atomic hydrogen sequence as a candidate for contamination removal in practical applications like photolithography at 13.5 nm radiation.