Preparation of ceria nanoparticles supported on carbon nanotubes

By chemical reaction of CeCl₃ and NaOH on carbon nanotube solution and subsequent heat treatment, ceria nanoparticles supported on carbon nanotubes were prepared. The processing parameters affecting the size of ceria particles were discussed. The particles were characterized by XRD and TEM. XRD patterns revealed that the particles exhibited CaF₂-type crystal structure. The TEM micrograph showed that the mean sizes of ceria particles were about 6 nm.     

Characterisation of high temperature oxidation using electron backscatter diffraction

Abstract

Electron backscatter diffraction (EBSD) in the scanning electron microscope (SEM) has been used to characterise the oxide scales formed on a low alloy steel. The technique provides a powerful combination of local phase information and orientational relationships both within and between phase layers. It has revealed that hematite grain growth occurs almost exclusively along the 0001 direction for the entire range of samples examined. Wüstite and magnetite grains were also found to grow preferentially along orientations close to the 001 direction.

EBSD is also well suited to characterising more complex scales such as those formed during hot working (e.g. millscale), and those formed on Fe–Ni alloys. In the latter complementary chemical information from energy dispersive spectroscopy (EDS), which was acquired simultaneously with the EBSD, enables the identity of crystallographically similar phases to be distinguished. EDS also shows that no nickel exists in the external scale and that it instead accumulates at the interface with the scale and at adjacent grain boundaries.     

Catalytic oxidation of carbon monoxide over radiolytically prepared Pt nanoparticles supported on glass

Platinum nanoparticles have been prepared by radiolytic and chemical methods in the presence of stabilizer gelatin and SiO₂ nanoparticles. The formation of Pt nanoparticles was confirmed using UV-vis absorption spectroscopy and transmission electron microscopy (TEM). The prepared particles were coated on the inner walls of the tubular pyrex reactor and tested for their catalytic activity for oxidation of CO. It was observed that Pt nanoparticles prepared in the presence of a stabilizer (gelatin) showed a higher tendency to adhere to the inner walls of the pyrex reactor as compared to that prepared in the presence of silica nanoparticles. The catalyst was found to be active at ≥150 °C giving CO₂. Chemically reduced Pt nanoparticles stabilized on silica nanoparticles gave ∼7% CO conversion per hour. However, radiolytically prepared Pt nanoparticles stabilized by gelatin gave ∼10% conversion per hour. Catalytic activity of radiolytically prepared platinum catalyst, coated on the inner walls of the reactor, was evaluated as a function of CO concentration and reaction temperature. The rate of reaction increased with increase in reaction temperature and the activation energy for the reaction was found to be ∼108.8 kJ mol⁻¹. The rate of CO₂ formation was almost constant (∼1.5 × 10⁻⁴ mol dm⁻³ h⁻¹) at constant O₂ concentration (6.5 × 10⁻³ mol dm⁻³) with increase in CO concentration from 2 × 10⁻⁴ mol dm⁻³ to 3.25 × 10⁻³ mol dm⁻³. The data indicate that catalytic oxidation of CO takes place by Eley-Rideal mechanism.     

Phase identification of oxide scale on low carbon steel

Abstract

The classical model of iron oxide scale layers; wüstite, magnetite and hematite, is more complicated in reality and its properties change with the factors that affect their development, such as time, temperature, alloying elements in the steel and oxidation environment. An understanding of the oxide scale formation and its properties can only be achieved by careful examination of the scale microstructure. Throughout this study, electron back-scatter diffraction (EBSD) has proved to be a powerful technique for verifying the individual phases in the oxide scale accurately. The results show that EBSD can be used to give a complete characterisation of the oxide scale formed on low carbon steel surface. Microstructural features such as grain size, shape and grain boundary characteristics have been successfully determined and analysed.     

Route to transition metal carbide nanoparticles through cyanamide and metal oxides

We have designed an efficient route to the synthesis of transition metal carbide nanoparticles starting from an organic reagent cyanamide and transition metal oxides. Four technologically important metal carbide nanoparticles such as tungsten carbide, niobium carbide, tantalum carbide and vanadium carbide were synthesized successfully at moderate temperatures. It is found that cyanamide is an efficient carburization reagent and that the metal oxides are completely transmitted into the corresponding carbide nanoparticles. A possible mechanism is proposed to explain the results of the reaction between cyanamide and the metal oxides.     

炭气凝胶负载Pt基催化剂的制备及其甲醇氧化催化性能

以间苯二酚(R)和甲醛(F)为原料,制备R-F炭气凝胶(RF-CAs).继以后者为载体采用浸渍还原法制备铂基催化剂Pt/CA,并比较其与由相同负载工艺制得的以Vulcan XC-72为载体的铂基催化剂Pt/XC72的催化甲醇氧化反应的性能.结果表明,前者具明显高的甲醇氧化催化活性,显示CAs是一种极具潜在竞争力的燃料电池催化剂载体材料.     

炭载Pt-P催化剂对甲醇氧化的电催化性能研究

通过NaH2PO2自分解方法制备了高分散性的Pt-P/C催化剂,并且使用X射线衍射(XRD)、透射电子显微镜(TEM)等表征手段对催化剂进行了表征,NaH2PO2的加入可有效降低催化剂的粒径,约为2.3nm。此外,亦用多种电化学测试手段测试了P的掺杂对甲醇的电催化氧化性能的影响,测试结果表明PtP/C催化剂不但能够增强催化剂对甲醇催化氧化的活性,而且还能够提高催化剂的稳定性。该测试结果表明Pt-P/C催化剂是一类具有潜在应用前景的直接甲醇燃料电池阳极催化剂。     

On the mechanism of carbon monoxide oxidation on the surface of gold nanoclusters supported on titanium oxide

The process of carbon monoxide (CO) oxidation on the surface of a system comprising nanodimensional gold clusters deposited onto thin films of titanium oxide of variable stoichiometry formed on a Re(1000) single crystal surface has been studied by methods of thermodesorption, IR, and X-ray photoelectron spectroscopy. It is established that oxygen contained in titanium oxide plays an important role in the conversion of CO into CO₂. The efficiency of this process on the Au/TiO _x (x < 2) system surface is significantly higher that that on the Au/TiO₂ system.     

活性碳纤维负载钴酞菁催化氧化2-巯基乙醇的研究

将四（2,4-二氯-1,3,5-三嗪基）氨基钴酞菁以共价键形式键合在活性碳纤维（ACF）载体上,制得了活性碳纤维负载钴酞菁催化剂（ACF-CoPc）,采用热重分析、原子吸收光谱和氮气等温吸附法对其进行了表征。原子吸收光谱测得金属酞菁的负载量为5.26μmol/g。氮气等温吸附法测得ACF-CoPc的比表面积为1235.9m2/g,孔径分布以2nm左右的小孔为主。以2-巯基乙醇为催化对象,采用超高效液相色谱研究了ACF-CoPc的催化氧化性能。结果表明ACF-CoPc对2-巯基乙醇具有很好的催化氧化性能,反应4h时对2-巯基乙醇的去除率高达100%,氧化产物为2,2’-二硫二乙醇。而且催化剂ACF-CoPc经6次循环使用后,对2-巯基乙醇的去除率没有持续下降,这表明该催化剂具有良好的重复使用性。     

Nickel-cobalt oxides/carbon nanoflakes as anode materials for lithium-ion batteries

Novel nickel-cobalt oxides/carbon nanoflakes with Ni/Co molar ratio = 1:1 and 1:2 have been synthesized by a convenient hydrothermal method followed by a simple calcination process. X-ray diffraction results showed that the composites were composed of NiO, Co₃O₄, and carbon. Scanning electron microscope measurements demonstrated that the composites were flakes less than 100 nm in thickness, and the corresponding energy dispersive spectroscopy mapping showed that the carbon was distributed homogeneously in the composites. The electrochemical results showed that the composite electrodes exhibited low initial coulombic efficiency and excellent charge-discharge cycling stability. Additionally, the effect of different Ni/Co molar ratios on the electrochemical properties of the composites was investigated, and better performance was obtained for the sample with a Ni/Co molar ratio of 1:2.     

Oxidation of carbon monoxide over Cu- and Ag-NaY catalysts with aqueous hydrogen peroxide

A novel oxidation reaction of CO with aqueous H₂O₂ over Cu-NaY (2-15 wt%) and Ag-NaY (5-15 wt%) catalysts has been achieved at low temperatures (55-70 °C) using a flow mode system. The employed catalysts were prepared by the incipient wetness impregnation of NaY zeolite (Si/Al = 5.6, surface area = 910 m²/g) with an aqueous solution of known concentrations of copper acetate and silver nitrate. Solids were subjected to thermal treatment at 300-450 °C prior to catalytic measurements unless subjected to subsequent reduction with hydrogen at 350 °C. The physicochemical characterization of the catalysts was probed using X-ray diffraction (XRD), FT-IR and combined thermal analyses TGA-DrTGA. The XRD data indicated that, the Ag particles have an ordered location in the sodalite cavity and the center of a single six-ring. The FT-IR data also proved the presence of a new peak at 1385 cm⁻¹ that is assigned to Ag-coordinated with the framework.A slow induced oxidation of CO (induction period, t_ind) took place at the initial stage of the CO oxidation reaction after which the reaction obeyed first-order kinetics. The utilized metal ions are proposed to be reduced to lower oxidation states such as Cu⁺ and Ag⁰ during the first period of reaction, t_ind, where the reaction proceeded favorably on such sites. Such argument was evidenced by carrying out the oxidation reaction over H₂-reduced Cu10-NaY and Ag10-NaY catalysts. The reduction caused a decrease in the t_ind, giving an evidence that the lower oxidation states Cu⁺ and Ag⁰ are the active sites in the studied oxidation reaction. The enhancement in catalytic activity was interpreted in terms of the facile adsorption of CO on the low oxidation state species.     

Corrosion surface protection by using titanium carbon nitride/titanium-niobium carbon nitride multilayered system

The aim of this work is the improvement of the electrochemical behavior of 4140 steel substrate using TiCN/TiNbCN multilayered system as a protective coating. We have grown [TiCN/TiNbCN]_n multilayered via reactive r.f. magnetron sputtering technique in which was varied systematically the bilayer period (Λ), and the bilayer number (n), maintaining constant the total thickness of the coatings (~ 3 μm). The coatings were characterized by X-ray diffraction (XRD), optical microscopy, electron microscopy and transmission electron microscopy assisted with selected area electron diffraction. The electrochemical properties were studied by Electrochemical Impedance Spectroscopy and Tafel curves. XRD results showed a preferential growth in the face-centered cubic (111) crystal structure for [TiCN/TiNbCN]_n multilayered coatings [1]. In this work was obtained the maximum corrosion resistance for the coating with (Λ) equal to 15 nm, corresponding to n = 200 bilayered. The polarization resistance and corrosion rate were around 8.6 kOhm cm² and 7.59 · 10^− 4 mm/year, these values were 8.6 and 0.001 times better than those showed by the uncoated 4140 steel substrate (1.0 kOhm and 0.57 mm/year), respectively. The improvement of the electrochemical behavior of the 4140 coated with this TiCN/TiNbCN multilayered system can be attributed to the presence of several interfaces that act as obstacles for the inward and outward diffusions of Cl^- ion species, generating an increment in the energy or potential required for translating the corrosive ions across the coating/substrate interface. Moreover, the interface systems affect the means free path on the ions toward the metallic substrate, due to the decreasing of the defects presented in the multilayered coatings.     

Acetylene decomposition to helical carbon nanofibers over supported copper catalysts

The helical carbon nanofibers (CNFs), synthesized at relatively low temperatures (lower than 250 °C) by using Cu as a catalyst, SiO₂, TiO₂, Al₂O₃, MgO as supports and acetylene as gas source, has been investigated.The products were characterized by field emission scanning electron microscope (FE-SEM), transmission electron microscope (TEM) and X-ray diffraction (XRD). The morphologies of obtained products influenced by the types of supports and weight ratios (Cu/support = 1:1, 1:5, and 1:10) were discussed. The average diameter of the helical CNFs was about 80 nm, and these CNFs had the same coil pitch, and coil diameter.     

Quaternary pyrite-structured nickel/cobalt phosphosulfide nanowires on carbon cloth as efficient and robust electrodes for water electrolysis

The strategy of element substitution is an effective way to tune the electronic structures of the active sites in catalysts,thereby leading to improvements in both the catalytic activity and stability.Herein,we design and synthesize pyrite-type nickel/phosphorus co-doped CoS2 nanowires on carbon cloth (NiCoPS/CC) as efficient and durable electrodes for water electrolysis.Introduction of nickel and phosphorus produced stepwise and superb enhancement of the performance of the electrodes in the hydrogen evolution reaction due to regulation of the electronic structures of the active sites of the catalyst and accelerated charge transfer over a wide pH range (0-14).The NiCoPS/CC electrodes also delivered a nearly undecayed catalytic current density of 10 mA.cm-2 at a low overpotential of 230 mV for oxygen evolution due to in situ formation of surficial Ni-Co oxo/hydroxide in 1.0 M KOH.Thus,the NiCoPS/CC electrodes gave rise to a catalytic current density of 10 mA.cm-2 for overall water splitting at potentials as low as 1.54 V during operation over 100 h in 1.0 M KOH with a Faradic efficiency of ～100％.     

Water Oxidation Catalysts for Artificial Photosynthesis

Water oxidation is the primary reaction of both natural and artificial photosynthesis. Developing active and robust water oxidation catalysts (WOCs) is the key to constructing efficient artificial photosynthesis systems, but it is still facing enormous challenges in both fundamental and applied aspects. Here, the recent developments in molecular catalysts and heterogeneous nanoparticle catalysts are reviewed with special emphasis on biomimetic catalysts and the integration of WOCs into artificial photosystems. The highly efficient artificial photosynthesis depends largely on active WOCs integrated into light harvesting materials via rational interface engineering based on in‐depth understanding of charge dynamics and the reaction mechanism.     

Optical properties of self assembled oriented island evolution of ultra-thin gold layers

Gold layers with a thickness of only 8 to 21 nm were sputtered on soda-lime-silica glasses. Subsequent annealing at 300 and 400 °C for 1 and 24 h resulted in the formation of separated round gold particles with diameters from 8 to 200 nm. Crystal orientations were described using X-ray diffraction and electron backscatter diffraction. The gold particles are oriented with their (111) planes perpendicular to the surface. Most gold nano particles are single crystalline, some particles are twinned. Thermal annealing of sputtered gold layers resulted in purple samples with a coloration comparable to that of gold ruby glasses. The color can be controlled by the thickness of the sputtered gold layer and the annealing conditions. The simple method of gold film preparation and the annealing temperature dependent properties of the layers make them appropriate for practical applications.     

Hydroformylation of alkenes over rhodium supported on the metal-organic framework ZIF-8

A highly porous and crystalline metal-organic framework （MOF） ZIF-8 has been synthesized and used for the preparation of a supported rhodium nanoparticle catalyst （Rh@ZIF-8）. The material has been characterized by PXRD, TEM, EDX, ICP-AES and nitrogen adsorption. The catalytic properties of Rh@ZIF-8 have been investigated in the hydroformylation of alkenes, with different chain length and structure, to give the corresponding aldehydes, and showed high activity. Furthermore, after the reaction was complete, the catalyst could be easily separated from the products by simple decantation and reused five times without a significant decrease in the activity under the investigated conditions.     

Immobilization of nanofibrous A- or B-site substituted LaMnO3 perovskite-type oxides on macroscopic fiber with carbon nanofibers templates

The immobilization of nanofibrous A- or B-site substituted LaMnO₃ perovskite-type oxides on macroscopic silica fiber via a unique and facile carbon nanofibers (CNFs) template-based method was reported. Field emission scanning electron microscopy (FE-SEM), coupled with X-ray diffraction (XRD) analysis confirmed the template effect and the existence of nanofibrous materials immobilized on silica fiber.     

Electrochemical deposition of precious metal on carbon nanotube for methanol oxidation

Precious metal nanoparticles were prepared on carbon nanotube (CNT) by sequential and simultaneous deposition methods for the electrocatalytic study of methanol oxidation. All electrochemical measurements were carried out in a three-electrode cell. A Platinum wire and Ag/AgCl were used as auxiliary and reference electrodes, respectively. Suspension of the CNT and Nafion were mixed and dropped on glassy carbon as a working electrode. Cyclic voltammograms in H₂SO₄ electrolyte solution are attributable to hydrogen adsorption and hydrogen desorption resulting in promising electrochemical performance of the prepared precious metal nanoparticles. Cyclic voltamograms of methanol electrooxidation studied in 2 M CH₃OH in 1 M H₂SO₄ show a distinguishing shape with a prominent oxidation wave in the anodic scan contributed to methanol oxidation while the cathodic scan is associated with the accumulation of carbonaceous species.     

负载型Pd催化剂的制备及其对甲醇氧化的催化活性

采用等体积浸渍法制备了一系列负载型Pd+M(M=MgO、CaO、SrO、BaO)催化剂,运用BET、CO-化学吸附、XRD、H2-TPR和XPS等表征手段对催化剂进行了表征,并考察其对甲醇的催化氧化性能。结果表明,添加碱土金属可使Pd粒子高度分散,催化剂表面易还原氧物种量增多,还原速率加快;XPS分析可知,碱土金属可增强Pd-Ce间相互作用,促使Pd向氧化态过渡,同时增加催化剂表面Ce3+浓度,改善催化剂的氧化还原性能,进而提高催化剂的催化活性。助催化效果递变规律为BaOCaOMgOSrO。