Dispersed Transition Metal Research Articles

XPS evidence for molybdenum nitride formation in ZSM-5

This communication presents XPS evidence for the formation of molybdenum nitride or oxynitride species in ZSM-5 when HZSM-5 loaded with MoO3 is subjected to temperature programmed reaction with ammonia. We suggest that this chemistry provides a potential route to zeolite dispersed transition metal nitride catalysts.

Dispersion and Solid State Ion Exchange of VCl3, CrCl3⋅6H2O, MnCl2⋅4H2O and CoCl2⋅6H2O onto the Surface of NaY Zeolite Using Microwave Irradiation

Transition metal/Y zeolites have been prepared by solid state ion exchange with microwave irradiation of mechanical mixtures of VCl3, CrCl3 ⋅ 6H2O, MnCl2 ⋅ 4H2O or CoCl2 ⋅ 6H2O with NaY zeolite at 900 W in 10–20 min. The prepared transition metal/Y zeolites were characterized by X-ray diffraction (XRD), infrared spectroscopy (IR), simultaneous thermal analysis (STA) and surface area measurement (BET). Concentration of dispersed transition metal on zeolite was measured and results revealed that transition metal was dispersed and ion exchanged onto the surface of NaY zeolite.

Transition Metal Modified TiO2-Loaded MCM-41 Catalysts for Visible- and UV-Light Driven Photodegradation of Aqueous Organic Pollutants

A number of transition metal (Cr, V, Fe, Cu, Mn, Co, Ni, Mo, and La) incorporated MCM-41 mesoporous molecular sieves with Si/Me = 80 have been synthesized by a hydrothermal method. It was demonstrated that the presence of transition metal salts in the gel during synthesis hinders the action of the template, which results in pores of MCM-41 that are not well-formed. These materials were then loaded with TiO2 via the sol−gel method, and the resulting materials were explored for the destruction of 4-chlorophenol in the presence of visible, as well as UV, light. A combination of various physicochemical techniques such as N2 physisorption, O2 chemisorption, X-ray diffraction (XRD), diffuse reflectance UV−vis (DR UV−vis), and temperature program reduction (TPR) were used to characterize the chemical environment of these transition metals in the prepared catalysts. The dispersion of transition metals as determined by O2 chemisorption suggests that they are well dispersed inside the MCM-41 framework, but the disp...

Exceptional electrochemical activities of amorphous Fe–B and Co–B alloy powders used as high capacity anode materials

Ultrafine amorphous alloy powders (UAAP) of Fe–B and Co–B were synthesized and tested for possible use as electroactive anodic materials. It is found that unlike their parent elements, the transition metal (TM) and boron, the Fe–B and Co–B alloy powders show superior electrochemical activities when used as anodic materials in aqueous alkaline solution. The discharge capacities of Fe–B and Co–B electrodes were observed to be 1200 and 1100 mAh/g at moderately high rate of 100 mAh/g, respectively, much higher than the theoretical capacity of currently used zinc metal (820 mAh/g). The exceptional high capacities of the boride alloys were found due to the electrochemical activation of boron atoms in the highly dispersed transition metal atoms. Inversely, the activated boron clamps the electrode potential to a negative region to prevent the transition metal from passivating.

Visible light photocatalysis in transition metal incorporated titania-silica aerogels

Transition metal salts were added to aerogels of TiO2–SiO2 mixtures. The resulting M–TiO2–SiO2 (M = transition metal, in general present in the form of oxides) materials had very high surface areas (600–1000m2/g) and pore volumes (1–4cm3/g), and contained highly dispersed transition metal oxides. Several samples were active photocatalysts for acetaldehyde oxidation to carbon dioxide using visible light; in particular chromium, cobalt, and nickel. These intimate aerogel mixtures were only active when SiO2 was present (i.e. M–TiO2 aerogels were not). High oxidation states of the transition metal ions (e.g. Cr6+, Co3+) appear to be important in bringing about visible light photocatalyst activity.

Characterization of Titania Loaded V-, Fe-, and Cr-Incorporated MCM-41 by XRD, TPR, UV−vis, Raman, and XPS Techniques

Transition metal (Me = V, Fe, and Cr) incorporated into MCM-41 mesoporous molecular sieves (Si/Me = 80) have been synthesized by hydrothermal methods and were loaded with TiO2 utilizing a sol−gel technique. These materials were found (refs 22, 23) to be photoactive for the destruction of organics with visible light. A combination of various physicochemical techniques such as N2 physisorption, O2 chemisorption, diffuse reflectance UV−vis (DR−UV−vis), X-ray diffraction (XRD), Raman, temperature program reduction (TPR), and X-ray photoelectron spectroscopy (XPS) were used to characterize the chemical environment of these transition metals in the prepared photocatalysts. The dispersion of transition metals as determined by O2 chemisorption suggests that they are well dispersed inside the MCM-41 framework, but the dispersion values decreased with the loading of TiO2. This indicates that the loaded titania promotes the transformation of incorporated metal ions into different phases. DR−UV−vis spectra of the Me-...

Oxidation of benzene to phenol on supported Pt-VO x and Pd-VO x catalysts

Gas-phase oxidation of benzene using a mixture of oxygen and hydrogen has been carried out on silica-supported vanadium oxide catalysts modified with platinum or palladium. Catalyst activity and phenol selectivity were studied as a function of the precious metal used, the vanadium oxide loading as well as of temperature. The binary catalysts have been characterized by TPR and TEM. Pt-VO x /SiO 2 catalysts were more active than Pd-VO x /SiO 2 catalysts. By using platinum catalysts benzene conversion amounted to 1.0% ( S phenol=97%) at 413 K, whereas palladium catalysts reached a conversion of only 0.2% ( S phenol=86%) for the same contact time and temperature. The most active catalyst for the oxidation of benzene to phenol was a low vanadium loaded 0.5 wt.% Pt–3 wt.% V on silica catalyst. At temperatures above 413 K phenol selectivity decreased strongly because of enhanced total oxidation. Active catalysts need both components: a dispersed transition metal oxide such as VO x as well as small precious metal particles such as platinum. The activity of the catalysts arises from a close interaction between the redox-active compound VO x and the electron mediator and hydrogen activator platinum as was confirmed by correlation of catalytic results and catalyst properties. Highly dispersed platinum particles are exclusively located on the vanadium oxide covered surface as demonstrated by TEM investigations. TPR studies showed and enhanced reducibility of a part of vanadium(V) oxide indication a close neighborhood of VO x and platinum.

Oxidation of cyclohexane with nanostructured amorphous catalysts under mild conditions

The oxidation of cyclohexane with molecular oxygen (1 atm) in the presence of isobutyraldehyde catalyzed by nanostructured iron and cobalt oxides and iron supported on titania has been studied. It was found that highly dispersed transition metals oxide is more effective for oxidation than the corresponding zero valent powders. In the titania supported catalysts iron exists as iron (III) oxide segregated to the surface layers and stabilized by titania. This form is the most active in the cyclohexane oxidation under mild conditions.

Role of defect structure in structural sensitivity of the oxidation reactions catalyzed by dispersed transition metal oxides

For dispersed transition metal oxides, the specific catalytic activity in the reactions of CO and hydrocarbons oxidation was compared with the densities of bulk and surface defects that were estimated using a combination of diffraction and spectroscopic methods. On this basis, the oxide systems were classified with respect to the scale and origin of the structural sensitivity manifestation. The results were discussed from the point of view of the atomic structure of the most developed surface faces of these oxides and their stoichiometry ranges. The most active surface sites were found to be associated with the surface extended defects including those located at the outlets of bulk extended defects.

Transition metal-aluminate catalysts for NO reduction by C 3H 6

Transition metal-aluminum mixed oxide catalysts (Cu, Ni and Co–Al 2O 3), with spinel-type structure, were prepared by coprecipitation method. These catalysts showed high activity and selectivity for the selective reduction of NO by C 3H 6 in excess oxygen, and showed moderate activity even in the presence of 10% water. Among the catalysts tested, Cu–Al 2O 3 with 16 wt.% Cu content exhibited the highest activity at low temperature, though a bend over of NO conversion was significant at high level of O 2 concentration. At low level of O 2 concentration, Cu–Al 2O 3 exhibited higher activity than Cu-ZSM-5 below 623 K. In addition, Cu–Al 2O 3 showed higher hydrothermal stability than Cu-ZSM-5. The high activity and selectivity of M-Al 2O 3 were attributed to the surface aluminate phase, containing highly dispersed transition metal cations in Al 2O 3 matrix.

Phase Formation during Anneal of Supersaturated TiB2–CrB2–WB2Solid Solutions

Numerous transition metal diborides of AlB2structure type reveal large mutual solid solubility. Temperature-depending homogeneity ranges bordering immiscibility gaps within the system TiB2–CrB2–WB2provide the opportunity to tailor anin situgrown typical platelet-shaped phase emerging from a supersaturated host matrix. Results are presented where variations in composition, manufacturing parameters, and heat treatment lead to precipitates of a “W2B5” structure accompanied by the formation of another tungsten boride less rich in boron in a (Ti, W, Cr)B2matrix. All phases are characterized by high melting points and hardness. The enhanced formation of the matrix as well as the precipitation mechanism were activated by the addition of 6 to 20 mole% CrB2to the system TiB2–WB2. Within the ternary solid solution, a particular composition range exists exhibiting a thermal expansion behavior similar to boron carbide. Attempts are made to toughen boron and silicon carbide ceramics by processing thisin situgrowth of platelets out of dispersed transition metal diboride particles within a carbide matrix.

Quantitative EPR studies of transition metal ions in oxide, aluminosilicate and polymer matrices

The importance of the proper choice of diamagnetic diluent used for preparation of standards for quantitative EPR measurements is shown by the example of CuSO4 and VOSO4 standards. The results of determination of the stability of chemical composition of VOSO4-K2SO4 standards stored for various periods of time, performed by different analytical methods, are compared. The examples are given to illustrate application of quantitative EPR measurements in the studies of structure and properties of transition metal ions dispersed in various matrices. Changes in the coordination sphere of surface transition metal ions occurring upon adsorption of gas molecules, the degree of dispersion of these ions and the extent of Mn+−Mn+ interactions derived from quantitative EPR measurements are described. The results of investigation of the mechanism of adsorption and catalytic reactions occurring on dispersed transition metal ions are presented.

Synthesis of Transition Metal Arsenides and Arsenic Metal Sulfides and Their Role in the Dearsenation of Shale Oils

One of the chief problems in upgrading shale oil is the presence of inherent arsenic, which is known to poison downstream catalysts. Highly dispersed transition metal sulfides formed in situ from the decomposition of dithiocarbamate (DTC) complexes of transition metals show excellent potential as dearsenation agents. We have studied the reaction of these sulfides with various arsenic compositions, and characterized the metal arsenides and arsenic metal sulfides formed as well as the ease of their formation. Thus, the reaction of bis(butyldithiocarbamato)Ni, (NiBuDTC), with model compounds was very facile and gave NiAs, NiAsS, and NiAs2-xSx. In general the effectiveness of the sulfides for dearsenation followed the sequence Ni > Mo ⪢ Co, while iron sulfides were totally ineffective. Based upon these results, tests where run in autoclaves (as well as a fixed-bed flow-through unit) with Ni BuDTC and shale oil having 73 ppm inherent As. Under optimum conditions, dearsenation down to less than 1 ppm was obtained.

Dehydrogenation activities of highly dispersed transition metal oxides on NaY zeolite

AbstractHighly dispersed α‐Fe2O3/NaY, NiO/NaY, and CuO/NaY catalyst systems were prepared by impregnation method. Dispersion thresholds of the transition metal oxides on NaY zeolite were determined by XRD phase analysis. The dispersion capacities of the transition metal oxides on NaY zeolite are much lower than that estimated on the basis of a closed packed monolayer in the micro pores. The catalytic activity and selectivity of the highly dispersed oxide catalyst systems for ethylbenzene and cyclohexane dehydrogenation reactions were reported.

Analysis of XANES for identification of highly dispersed transition metal oxides on supports

XANES of vanadium and niobium oxide on silica or alumina have been analyzed quantitatively by a deconvolution technique. Based on the results for reference compounds, local structures of supported vanadium and niobium species were identified. The composition was estimated from difference spectra for the samples which consisted of two kinds of species.

Sialons and Silicon Nitrides; Microstructural Design and Performance

ABSTRACTsurvey is presented of developments in silicon nitride and sialon ceramic microstructures designed for application in differing temperature regimes.For low temperature (< 1000°C) application, pressureless-sinterable sialons with moderate (10-15%) intergranular glass, anisotropic β′ grains and high values of MOR and Kc (1 GPa and 6-10MPa| m respectively) are preferred.Improved hardness and high temperature capability may be achieved by tailoring intergranularp hases for crystallisation and further enhanced by the introduction of mixed α′/β′ Sialon microstructures. Examples are given of microstructural evolution in β′- Y3Al5O12(garnet), β′-Nd3Si3Al3O12N2 and α′/β′/garnet ceramics and a comparison of their mechanical behaviour.Novel Sialon ceramics containing dispersed transition metal compounds (TiN, TiB2) may be formed by in-situ redox reaction, utilising the α′ Sialon phase as an oxygen receptor. The dispersed phase may enhance hardness and toughness and confer electro-discharge machinability.Oxidation instability of Sialon compositions dictates the use of diphasic Si3N4/M2Si2O7 microstructures for application above 1300°C. The thermal cycle during pressurised sintering of these non-sialon compositions is critical in avoiding crystallisation of mixed polymorphs of the intergranular disilicate, with consequent microcracking.

Activity of highly dispersed transition metal oxides formed in Y zeolite for toluene oxidation

The activities of various transition metal ion-exchanged Y zeolites treated with NaOH solution were investigated in terms of complete oxidation of diluted toluene in air. The highly dispersed metal oxides were formed by soaking CrY, NiY, FeY, MnY, CuY, and CoY with the NaOH solution at pH 11.0 and 298 or 273 K, followed by calcination at 573 K in air. The NaOH-treated CoY exhibited the highest activity for toluene oxidation. This excellent activity could be ascribed to less stable oxygen species than those on the crystalline Co3O4.

Enhanced reactivity of metal-impregnated peat char and semi-coke during gas phase hydrogenolysis

Methane formation in the reaction between peat-derived chars and hydrogen was studied using peat semi-coke and doped chars. The latter were prepared by ion exchange of the initial material prior to pyrolysis. Impregnation with relatively large amounts of finely dispersed transition metals (up to ≈15 wt%) results in significant enhancement of methane production. Devolatilization prior to hydrogenolysis exerts a marked influence on the behaviour of the char due to its effect on the concentration of surface oxygen species. The lower the devolatilization temperature, the higher the methane yield. Two distinct peaks are present during the methane formation: a low-temperature peak involving the presence of CO and a high-temperature peak related to the direct reaction between H 2 and the char. The conversion profiles could be well approximated by a two-parameter model.

銅 電気伝導材料に対する有機金属錯体 添加の影響

In the present study particle powders of copper coated with thin films of organometallic complexes were pressed and then heat treated. The complex compounds were thermally decomposed to carbide particles of uniform dimension or to fine oxide particles; these particles were homogeneously dispersed in the alloys, thus permitting the production of the conductive materials having fairly low or negative temperature gradient of resistance to keep high conductivity at higher temperature. It may be said that this type of new conductive materials overthrows the Matthissen's rule. Thus deviation from the Matthissen's rule is particularly re-markable in the samples added with Ni(AA)2, Ti(AA)3, 1Mn4Ni(AA)2 and SmCo5(AA)2. This deviation may be attributed to s-d interaction of the dispersed amorphous transition metal compounds and matrix copper atoms.