A Mössbauer study of iron-containing phases in a vanadium oxide catalyst for the oxidation of sulphur dioxide in sulphuric acid production

The iron-containing phases in fresh and partly deactivated vanadium oxide catalyst are identified by Mössbauer spectroscopy. As a result of exploitation of the catalyst the new phases of Fe₃O₄, FeSO₄ and Fe₂(SO₄)₃ alongwith presence of α-Fe₂O₃ are formed. The Mössbauer spectroscopy presents new possibilities for studying the composition changes in iron-containing phases, and provides a tool to reveal the reasons leading to deactivation of industrial vanadium catalysts.     

氢离子辐照纯钒中形成的位错环

钒合金作为聚变堆候选材料, 其辐照损伤行为一直是关注的重点. 研究辐照时形成的位错环的性质, 其意义在于揭示纯钒中辐照空洞的长大机理. 这种机理表现为不同类型位错环对点缺陷吸收的偏压不同, 从而影响金属的辐照肿胀. 本文利用加速器对纯钒薄膜样品进行氢离子辐照, 然后, 利用透射电镜的inside-outside方法分析氢离子辐照所形成的位错环的类型. 结果表明, 在氢离子辐照纯钒中没有发现柏氏矢量b=<110>的位错环, 只有柏氏矢量b=1/2<111>和b=<110>的位错环, 这两种位错环的惯性面处于{110}-{112}之间. 能确定性质的位错环全部为间隙型位错环, 未发现空位型位错环.     

镍钒复合光催化剂的光谱特征及其光催化性能

以SiO2、活性炭(AC)和Al2O3为载体,采用浸渍法制备了Ni-V-O系负载光催化剂.考察了样品的光谱特征,并在紫外光下评价了样品在甲醇和CO2光催化反应巾的性能;通过吡啶吸附FIIR和UV-Vis分析,结合反应测试结果,比较了催化剂载体对产物选择件的影响.XRD结果表明,在系列催化剂中,SiO2载体上的镍、钒粒子分散程度最高.吡啶吸附FIIR结果显示,系列催化剂表面存在L酸中心;相同的活性组分由于载体不同,所得到的负载催化剂表面酸度不同.负载催化剂表面L酸强度顺序为:Ni-V-O/SiO2>Ni-V-O/Al2O3>Ni-V-O/AC.不同酸度的催化剂,其上的羰基化产物甲酸甲酯(MF)和碳酸二甲酯(DMC)的选择性也不同.催化剂的表面酸强度是影响羰基产物选择性的主要因素.     

Pillar effects in MoS2 catalysts supported on Al and Zr pillared clays in a hydrotreatment reaction: A preliminary study

Molybdenum (Mo) supported on aluminum-pillared clay (Al-PILC) and zirconium-pillared clay (Zr-PILC) with contents of 0.6, 1.4 and 2.8 atoms of Mo/nm² were prepared and tested in the hydrogenation (HYD) of naphthalene (NP). It was found that the molybdenum sulfide (MoS₂) catalysts supported on Zr- pillared clays were more active than the samples supported on Al-pillared clays and catalysts supported on alumina. The catalysts were characterized by X-ray diffraction (XRD), thermogravimetric analysis, nitrogen adsorption and transmission electron microscopy (TEM). Characterization analysis clearly pointed out to a close interaction of MoS₂ with ZrO₂ in the pillared clays. Therefore, the highest hydrogenation activities can be related to the presence of an interaction of MoS₂ with ZrO₂, probably with a different electronic interaction between the active phase and the support, than that reported for the MoS₂/Al₂O₃ system.     

Pseudo-copper Ni–Zn alloy catalysts for carbon dioxide reduction to C2 products

Electrocatalytic CO₂ reduction reaction (CO2RR) to obtain C₂ products has drawn widespread attentions. Copper-based materials are the most reported catalysts for CO₂ reduction to C₂ products. Design of high-efficiency pseudo-copper catalysts according to the key characteristics of copper (Cu) is an important strategy to understand the reaction mechanism of C₂ products. In this work, density function theory (DFT) calculations are used to predict nickel–zinc (NiZn) alloy catalysts with the criteria similar structure and intermediate adsorption property to Cu catalyst. The calculated tops of 3d states of NiZn3(001) catalysts are the same as Cu(100), which is the key parameter affecting the adsorption of intermediate products. As a result, NiZn3(001) exhibits similar adsorption properties with Cu(100) on the crucial intermediates *CO₂, *CO and *H. Moreover, we further studied CO formation, CO hydrogenation and C–C coupling process on Ni–Zn alloys. The free energy profile of C₂ products formation shows that the energy barrier of C₂ products formation on NiZn3(001) is even lower than Cu(100). These results indicate that NiZn3 alloy as pseudo-copper catalyst can exhibit a higher catalytic activity and selectivity of C₂ products during CO₂RR. This work proposes a feasible pseudo-copper catalyst and provides guidance to design high-efficiency catalysts for CO₂RR to C₂ or multi-carbon products.     

Growth and characterization of model oxide catalysts

Oxide catalysts are frequently used to convert toxic species to environmentally benign molecules, and to prevent the formation of toxic species in the first place. In this paper, growth and characterization of model oxide systems employed in both approaches is discussed. An example of the former approach is the selective catalytic reduction (SCR) of NO emitted from power plants by NH₃, which employs tungsten and vanadium oxides supported on the anatase polymorph of TiO₂. To model SCR catalysts, epitaxial titanium, vanadium and tungsten oxide films were grown using molecular beam epitaxy and magnetron sputtering. Two different anatase orientations were grown on LaAlO₃ substrates and their interactions with vanadia were characterized. On LaAlO₃ (0 0 1), anatase exposed a (4 × 1) reconstructed (0 0 1) surface. Vanadia lifted the reconstruction and at 1 ML a (1 × 1) surface with mostly V⁵⁺ was observed. Continued V₂O₅ growth led to loss of order, but at high temperatures epitaxial VO₂ could be grown; vanadia behaved similarly on anatase films on LaAlO₃ (1 1 0). Results suggested that the monolayer is pseudomorphic with O adsorption oxidizing the surface V to 5+, since the anatase structure cannot accommodate more bulk oxygen, only a monolayer can be pseudomorphic and have only V⁵⁺. Thus the vanadia monolayer has unique structural and chemical properties that can help explain why vanadia monolayers on TiO₂ are much more active than bulk V₂O₅. For WO₃, a series of added row reconstructions were observed as the epitaxial films were reduced. The effect of these structures on surface chemistry was characterized by studying 1-propanol adsorption. The results indicated that the structure of the WO₃ surface did not alter its catalytic function but had a strong effect on reaction kinetics. As an example of a system where catalysts prevent the formation of toxic species, the reactivity of oxidized Pd surfaces used in CH₄ catalytic combustion were studied. An ordered PdO-like monolayer was found to be less reactive towards CO than adsorbed O on Pd. On the other hand, the PdO layer favored a lower activation energy C₃H₆ oxidation pathway. The results indicated that Pd oxidation reduces the sticking coefficient of reactive species but once molecules adsorb, the oxide surface can reduce the activation energy for subsequent reaction.     

The surface structure of catalysts activated with hydrogen donors as elucidated by multinuclear solid-state NMR

¹H, ²⁷Al and ³¹P MAS, and ¹³C and ²⁹Si CP/MAS NMR spectroscopies, were used to characterize catalysts of Pd supported on various solids including SiO₂, AlPO₄ and Mg₃(PO₄)₂ that were activated with the chiral hydrogen-donor limonene. The above-mentioned techniques were used to check for the formation of an organopalladium complex between Pd²⁺ atoms and the olefin bonds in the limonene molecule on the catalyst surface. The results are compared with those obtained for catalysts activated in a hydrogen stream.     

室温合成非晶三硫化钼析氢催化剂的性能调制以及其在串联制氢器件中的应用

高催化活性、低成本、良好工艺兼容性以及高稳定性的析氢催化剂是实现一体化光电化学水解制氢器件的关键, 然而传统的贵金属催化剂由于储量稀缺、成本高昂而严重限制了光电化学水解制氢器件的产业化进程. 本文在室温下通过湿法化学合成法制备了高催化活性、成本低廉以及工艺兼容性好的非金属非晶三硫化钼析氢催化剂, 并研究了不同催化剂滴涂量对其催化活性以及串联制氢器件制氢性能的影响. 结果表明, 存在最优化非晶三硫化钼催化剂滴涂量以获得最佳催化活性(10 mA/cm²电流密度对应电势达260 mV vs. RHE(可逆氢电极), 塔菲尔斜率达68 mV/dec), 其粗糙表面以及多孔结构可获得更大的电化学接触面积以促进析氢反应. 进一步将其作为光阴极应用于串联制氢器件, 可有效降低过电势损失和提高光生电流密度输出, 与光阳极结合有望提高制氢效率.     

石墨烯增强半导体态二氧化钒近场热辐射

本文基于涨落耗散定理和并矢格林函数求解麦克斯韦方程来研究两个半无限大平板的近场热辐射净热流,提出了两个半无限大块状二氧化钒组成的V/V结构、石墨烯覆盖两个半无限大块状二氧化钒组成的GV/GV结构和石墨烯覆盖VO2薄膜组成的GV0/GV0结构,深入研究了这三种结构中二氧化钒与石墨烯间的近场热辐射,并分析了真空间距、二氧化钒薄膜厚度和石墨烯化学势等物理参量变化对近场热辐射的影响.研究表明:三种结构的近场热辐射均随间距增大而减小;在真空间距为10 nm时,由石墨烯覆盖的GV/GV结构的近场辐射热流比无石墨烯覆盖的V/V结构增强35倍,耦合效果最好的是GV0/GV0结构,该结构的近场辐射热流比GV/GV结构增强8.6倍;在GV0/GV0结构中,当二氧化钒薄膜厚度为30 nm时,石墨烯化学势从0.1 eV增加到0.6 eV辐射热流会减小3.3倍.本文系统研究了二氧化钒与石墨烯间相互耦合的近场热辐射,对相关结构的近场热辐射实验和实际应用具有理论指导意义.     

Effect of Ag promoter on redox properties and catalytic performance of Ag-Mo-P-O catalysts for oxidative dehydrogenation of propane

The influence of addition of sliver ions on the redox properties and catalytic performance of molybdenum-phosphate catalyst in oxidative dehydrogenation (ODH) of propane has been investigated. MoO₃ and AgMoO₂PO₄ have been detected in Ag-doped Mo-P-O catalysts. The redox properties have been characterized by H₂-temperature-programmed reduction (TPR), electronic paramagnetic resonance (EPR) and X-ray photoelectron spectroscopy (XPS). The catalytic performance of MoO₃, Ag₂O, AgMoO₂PO₄ and Ag-doped Mo-P-O catalysts has also been examined. The incorporation of Ag improved the number of Mo⁵⁺ species and the reducibility of the catalysts. The Ag-doped catalysts favor activity and selectivity in ODH of propane higher than the undoped catalyst. The best catalyst was obtained with Ag/Mo ratio of 0.3 and MoO₃/AgMoO₂PO₄ ratio of 1.1. The influence of promoter Ag⁺ on redox properties and catalytic performance is due to forming redox couple “Ag⁰+Mo⁶⁺Ag⁺+Mo⁵⁺” and the synergetic effect originating from “coherent interface” between MoO₃ and AgMoO₂PO₄.     

XPS characterization of supported Ziegler-Natta catalysts

Surface analytical technique ESCA (electron spectrometer for chemical analysis) has been used for analysis of catalysts used in propylene polymerization. As a result of this analysis it has been shown that productivity of a catalyst can be correlated to Ti/Mg atomic ratio that indicates dispersion of titanium atoms on magnesium support. A quantitative indicator of productivity, i.e. “titanium index” has also been evaluated for studied catalysts.     

Towards the preparation of realistic model Ziegler-Natta catalysts: XPS study of the MgCl2/TiCl4 interaction with flat SiO2/Si(1 0 0)

Despite of the wide use of supported Ti based Ziegler-Natta catalysts in the olefin polymerization industry, questions concerning the role of each one of the catalyst components in the polymerization process, have not found a satisfactory answer yet. This is mainly because of the high sensitivity of these systems to oxygen and atmospheric moisture that makes their study in an atomic level rather complicated. Realistic surface science models of the pre-activated SiO₂ supported MgCl₂/TiCl₄ and TiCl₄ Ziegler-Natta catalysts were prepared by spin coating on flat conductive SiO₂/Si(1 0 0) supports under inert atmosphere. This preparation technique resembles the wet chemical impregnation which is the industrial method of the catalyst preparation. XPS analysis showed that the catalyst precursor anchors on the silica surface through bonding of the Ti atoms with surface silanes or siloxanes, while Mg is attached to the Ti through chlorine bridges. Thermal treatment of the catalysts at 723 K leads to total Cl desorption when MgCl₂ is not present while a significant amount of the Ti atoms is reduced to the Ti³⁺ state.     

Electrochemical behaviour of oxygen at nickel nest cathodic material with catalyst La1−xSrxCoO3

The reduction of oxygen in the three phases gas–liquid–solid using a nickel nest as electrode with a La_1−xSr_xCoO₃ (x=0, 0.3, 0.5, 0.7, 1) series of combined oxides as a catalyst in different electrolytes of acidic H₃PO₄ or alkaline KOH, NaOH or LiOH solution at a fixed optimum oxygen flow-rate at room temperature was studied by the electrochemical method. The electrochemical parameters, such as electron transfer coefficient and exchange current density, were also determined. The La_1−xSr_xCoO₃ series of catalysts was synthesized by a solid-state reaction. XRD was used to confirm the structure of the catalyst. BET, EDS and resistivity measurements were used to investigated the electrochemical behaviour of the cathodic reduction of oxygen in the presence of the catalyst. SEM was also used to inspect the change before and after the reaction with the catalyst. The electron transfer coefficients, β, from the experiments with the various catalysts in the different alkaline electrolytes were determined as follows:

β(in KOH)>β(in NaOH)>β(in LiOH).

It was discovered that La_0.7Sr_0.3CoO₃ as a catalyst has a higher catalytic activity, a higher specific surface area, lower electrical resistivity, better stability and less agglomeration. Therefore, the above catalyst is the best catalyst for oxygen reduction of those studied.     

Variation of the vanadium oxidation state within a VPO catalyst layer in a membrane reactor: XPS mapping and modelling

Recently, the feasibility of butane oxidation in an electrochemical membrane reactor (EMR) using a vanadium phosphorus oxide (VPO) catalyst layer on a tubular anodic electrode has been reported. This novel application of EMR gives rise to questions about the vanadium oxidation state (V_ox) under working conditions and about its spatial distribution in the catalyst layer. It has now been determined by means of position-resolved XPS measurements. In addition, model calculations on the spatial V_ox distribution have been performed for the first time. The simulations reveal a non-uniform 3D distribution of V_ox due to the relative rate of reduction and re-oxidation processes in the catalyst layer, in good agreement with the experimental XPS data.     

High-throughput screening of binary catalysts for oxygen electroreduction

A series of Pt based and non-Pt catalysts for proton exchange membrane fuel cell (PEMFC) and direct methanol fuel cell (DMFC) have been evaluated towards oxygen reduction, by high-throughput optical screening. Fluorescein was first used as pH indicator for detecting pH change of the electrolyte in the vicinity of cathode caused by oxygen reduction. Arrays of catalyst spot comprised of binary catalysts and pure Pt were prepared by using robotic micro-dispenser. The analysis of fluorescence images has showed that some of Pt based catalysts including PtBi, PtCu, PtSe, PtTe and PtIr, as well as RuFe, as a non-Pt catalyst, exhibited higher activities and methanol tolerance than pure Pt. Moreover, acceptable stability of these catalysts at high potential in acid environment suits them to the requirements of cathode catalyst in PEMFC or DMFC.     

The synthesis and regeneration of palladium catalysts with the use of supercritical carbon dioxide

The solubility of palladium chloride complexes with organic ligands in supercritical carbon dioxide (SC-CO₂) was measured. The possibility of using SC-CO₂ as a working medium for the preparation and regeneration of deposited palladium catalysts was studied. The active catalyst component was deposited from solutions of palladium chloride complexes with organic ligands in SC-CO₂. The regeneration of catalysts deactivated during the hydrogenation of acetylene in an ethane-ethylene mixture was also performed in SC-CO₂ with varying process conditions. A comparison of the specific surface areas and activities of freshly prepared and regenerated samples showed that the methods suggested were highly competitive compared with the traditional regeneration techniques.     

掺钨VO_2薄膜的电致相变特性

采用直流磁控溅射与后退火工艺相结合的方法,在掺氟SnO_2(FTO)导电玻璃基底上制备了高质量的掺钨VO_2薄膜,对薄膜的结构、表面形貌和光电特性进行测试,分析了钨掺杂对其相变性能的影响.结果表明,室温下掺钨VO_2薄膜的阈值电压为4.2 V,观察到阈值电压下约有两个数量级的电流突变.随着温度升高,相变的阈值电压降低,且电流突变幅度减小.当施加8 V电压时,分别在不同温度下测试了掺钨VO_2薄膜的透过率.温度为20和50℃时,掺钨VO_2薄膜相变前后的红外透过率差量分别为23%和27%.与未掺杂的VO_2薄膜相比,掺钨VO_2薄膜具有相变温度低、阈值电压低和电阻率小的特点,在高速光电器件中有广阔的应用前景.     

固体核磁共振技术在甲醇制烯烃反应中的应用

甲醇制烯烃过程是由非石油路线生成低碳烯烃的重要途径之一.分子筛因具备独特的孔结构和可调变的酸性质,而成为甲醇制烯烃过程的核心催化剂.固体核磁共振(NMR)是鉴定物质结构、阐释催化反应机理的强有力的工具,在甲醇制烯烃的研究中被广泛应用.本文主要总结了近年来利用原位固体NMR、多维多核NMR、脉冲梯度场NMR等固体NMR技术研究甲醇制烯烃反应机理取得的重要进展.原位固体NMR可以在真实反应条件下监测催化反应中反应物、中间体和产物的动态演变过程;多维多核NMR可以在不破坏催化剂结构情况下确定反应中间体结构信息,特别是¹²⁹Xe NMR可以很灵敏探测反应中催化剂的孔道结构变化;脉冲梯度场NMR可用于测定孔道内分子的扩散系数,阐明分子筛的扩散机制.     

A rational design of bimetallic PdAu nanoflowers as efficient catalysts for methanol oxidation reaction

Methanol fuel cells have been intensively developed as clean and high-efficiency energy conversion system due to their high efficiency and low emission of pollutants. Here, we developed a simple aqueous synthetic method to prepare bimetallic Pd Au nanoflowers catalysts for methanol oxidation reaction(MOR) in alkaline environment. Their composition can be directly tuned by changing the ratio between Pd and Au precursors. Compared with commercial Pd/C catalyst, all of the Pd Au nanoflowers catalysts show the enhanced catalytic activity and durability. In particular, the Pd Au nanoflowers specific activity reached 0.72 m A/cm2, which is 14 times that of commercial Pd/C catalyst. The superior MOR activity could be attributed to the unique porous structure and the shift of the d-band center of Pd.     

From fundamental studies of reactivity on single crystals to the design of catalysts

One of the prominent arguments for performing surface science studies have for many years been to improve and design new and better catalysts. Although surface science has provided the fundamental framework and tools for understanding heterogeneous catalysis until now there have been extremely few examples of actually designing new catalysts based solely on surface science studies. In this review, we shall demonstrate how a close collaboration between different fundamental disciplines like structural-, theoretical-and reactivity-studies of surfaces as well as a strong interaction with industry can have strong synergetic effects and how this was used to develop a new catalyst. As so often before the studies reviewed here were not initiated with the objective to solve a specific problem, but realizing that a new class of very stable two-dimensional alloys could be synthesized from otherwise immiscible metals made it possible to present a new solution to a specific problem in the industrial catalysis relating to methane activation in the steam reforming process. Methane is the main constituent of natural gas and it is an extremely important raw material for many large scale chemical processes such as production of hydrogen, ammonia, and methanol. In the steam reforming process methane and water are converted into a mixture of mainly hydrogen and carbon monoxide, the so-called synthesis gas. Industrially the steam reforming process usually takes place over a catalyst containing small nickel crystallites highly dispersed on a porous support material like aluminum/magnesium oxides in order to achieve a high active metal area. There is a general consensus that the rate limiting step of this process is the dissociative sticking of methane on the nickel surface. Driven by the desire to understand this step and hopefully be able to manipulate the reactivity, a large number of investigations of the methane/nickel interaction have been performed using nickel single crystals as model catalysts. The process has been investigated, both under thermal conditions and by using supersonic molecular beams elucidating the dynamical aspects of the interaction. The results obtained will be reviewed both with respect to the clean and modified nickel surfaces. Especially the two-dimensional gold–nickel alloy system will be considered since the fundamental results here have lead to the invention of a new nickel based catalyst, which is much more resistant to carbon formation than the conventional nickel catalysts. This may be one of the first examples of how fundamental research can lead to the invention of new catalysts. Other overlayer/alloy combinations, their stability, and reactivity are briefly discussed with respect to manipulation of the surface reactivity towards methane.