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1.
The ignition processes for the catalytic partial oxidation of methane (POM) to synthesis gas over oxidic nickel catalyst (NiO/Al 2O 3), reduced nickel catalyst (Ni 0/Al 2O 3), and Pt-promoted oxidic nickel catalyst (Pt–NiO/Al 2O 3) were studied by the temperature-programmed surface reaction (TPSR) technique. The complete oxidation of methane usually took place on the NiO catalyst during the CH 4/O 2 reaction, even with a pre-reduced nickel catalyst, and Ni 0 is inevitably first oxidized to NiO if the temperature is below the ignition temperature. It is above a certain temperature that Ni 0 is formed again, which leads to the start of the POM. The POM can be initiated at a much lower temperature on a Pt–NiO catalyst because of Pt promotion of the reduction of NiO. The POM in a fluidized bed can be easily initiated due to the addition of Pt. 相似文献
2.
Herein, intrinsic p-type conductivity of NiO films were enhanced by high power impulse magnetron sputtering (HiPIMS) technology, where more charged Ni 3+ ions are created during the deposition process. The formation of Ni 3+ ions are advantageous for strengthening the p-type conductivity of NiO films. As the pulse off-time increases from 0 μs to 3000 μs, Ni 3+ concentration improves greatly, indicating the amount of Ni vacancies as well as the hole concentration significantly enhances. It confirms that HiPIMS is a preferential technology for preparing NiO films with high p-type conductivity. Especially, when pulse off-time reaches 3000 μs, a high carrier concentration of 2.86 × 10 21 cm −3 and a relatively low electrical resistivity about 0.07 Ω·cm are achieved. 相似文献
3.
The capability of wheat straw to adsorb Ni 2+ and Zn 2+ was investigated using a batch system. The equilibrium removal of metal ions was obtained between 2.5 and 5 h for Ni 2+ and about 3 h for Zn 2+ over the initial concentration range from 5 to 150 ppm. Of the total amount of metal uptake by wheat straw, about 50% was adsorbed in the first 30 min. At a low initial concentration of 5 ppm, wheat straw was capable to reduce the metal concentration down to less than 1 ppm. For single-metal solutions, among the three models tested, namely the Langmuir, the Freundlich and the Temkin isotherms, the Freundlich model was suitable to describe the adsorption equilibrium for Ni 2+ and Zn 2+. For bimetal solutions, the IAST-Freundlich multicomponent isotherm best fitted the experimental data, among the four isotherm models investigated, the modified Langmuir multicomponent model, the Langmuir partially competitive model, the Freundlich multicomponent model and the IAST-Freundlich multicomponent model. The negative Gibbs free energy changes obtained at lower concentrations indicates that the adsorption was spontaneous. However, the spontaneity of the biosorption decreased with increases in the metal concentration from 5 to 50 ppm. For metal concentrations higher than 50 ppm, the adsorption became non-spontaneous. Scanning electron microscopic (SEM) images of wheat straw were also taken to exam the surface structure of the wheat straw along with the energy dispersive spectrum (EDS) analysis. The results obtained confirmed the adsorption of Ni 2+ and Zn 2+ on wheat straw, and showed that the inner surface of the wheat straw appeared to provide more adsorption sites for metal binding. 相似文献
4.
The ferrous oxidation ability of Acidithiobacillus ferrooxidans was studied in the presence of Ni 2+, V 4+ and Mo 6+ in 9 K media in order to implement the culture in the bioleaching of spent catalyst. The rate of iron oxidation decreased
with increasing concentration of metal ions, but the rate of inhibition was metal-ion dependent. The tolerance limit was critical
at a concentration of 25 g/L Ni 2+, 5 g/L V 4+ and 0.03 g/L Mo 6+. The growth rate of microorganisms was negligible at concentrations of 6 g/L V 4+ and 0.04 g/L Mo 6+. Levels and degree of toxicity of these ions have been quantified in terms of a toxicity index (TI). The toxicity order of
metal ions was found to be Mo 6+>V 4+>Ni 2+. The significance and relevance of multi-metal ion tolerance in Acidithiobacillus ferrooxidans has been highlighted with respect to bioleaching of spent refinery catalyst. 相似文献
5.
The distribution of Ni 2+ ions in NiO‐doped 10YSZ powder is examined with Superconducting Quantum Interference Device magnetometry, a technique that is able to distinguish between randomly distributed Ni 2+ ions in solid solution and ordered Ni 2+ ions within NiO with high precision. Very high purity powders containing 0.01, 0.1, 0.5, and 1.0 mol% NiO in 10YSZ (all levels below the solid solubility limit of NiO in 10YSZ) were made from acetate precursors and a modified EDTA (ethylenediaminetetraacetic acid)‐citrate synthesis method. The powders were calcined in air at either 873 or 1273 K. The 873 K calcination leads to single phase YSZ particles about 10 nm in diameter, and almost all of the NiO dopant exists in complete solid solution. The 1273 K calcination leads to a larger YSZ particle size (55–95 nm), and also to the formation and/or growth of NiO particles, the amount of which depends on the length of time of calcination. Upon sintering the powders in air (1773 K, 1 h), the NiO dissolves back into 10YSZ. The results demonstrate that particle growth during calcination leads to the exsolution of Ni 2+ ions to form NiO. This has important implications for the synthesis of NiO‐doped 10YSZ from chemical precursors. 相似文献
6.
The influence of Na-pretreatment of γ-Al 2O 3 on the catalytic oxidation of CO over NiO/Al 2O 3 was investigated. The effect of such treatment on the concentration of the catalytically active phase (NiO) in the uppermost surface layers of the catalyst was also studied by the X-ray photoelectron spectroscopic investigation of various solids.The results revealed that the addition of Na 2O (0.45 wt%) decreased the catalytic activity (reaction rate constant per unit surface area) of the pretreated solid. However, the activity was found to increase monotonically by increasing the amount of sodium added in the range 1.35–6 wt%. The sodium-pretreatment of γ-Al 2O 3 resulted in a decrease in the concentration of Ni on the catalyst surface to an extent proportional to the amount of Na2O present. These findings have been attributed to blocking of some sites of Al2O3 surface by Na+ ions thus decreasing the amount of Ni 2+ ions retained on its surface. The observed increase in catalytic activity of sodium-treated solid (containing more than 0.45 wt%) might be due to dissolution of some Na + ions in the NiO lattice which lowered its Fermi-level, leading to an increase in the degree of p-type semiconducting character of the doped NiO catalyst. 相似文献
7.
This paper concerns the relation between surface structure of crystalline vanadia-like active species on vanadia–tungsta catalyst
and their activity in the selective reduction of NO by ammonia to nitrogen. The investigations were performed for Ti–Sn-rutile-supported
isopropoxy-derived catalyst. The SCR activity and surface species structure were determined for the freshly prepared catalyst,
for the catalyst previously used in NO reduction by ammonia (320 ppm NO, 335 ppm NH 3 and 2.35 vol% O 2) at 573 K as well as for the catalyst previously annealed at 573 K in helium stream containing 2.35 vol% O 2. The crystalline islands, exposing main V 2O 5 surface, with some tungsten atoms substituted for V-ones, were found, with XPS and FT Raman spectroscopy, to be present at
the surface of the freshly prepared catalyst. A profound evolution of the active species during the catalyst use at 573 K
was observed. Dissociative water adsorption on V 5+OW 6+ sites is discussed as mainly responsible for the catalyst activity at 473 K and that on both V 5+OW 6+ and V 4+OW 6+ sites as determining the activity at 523 K.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
8.
Chitosan, which is produced from the natural polymer chitin, is a much more efficient scavenger of nickel ion than other natural ion exchange materials tested. An industrial waste containing about 7 ppm Ni 2+ and 10,000 ppm Na + was reduced to less than 0.1 ppm Ni 2+ by contact in a packed column of chitosan. Capacity of the chitosan substrate under these conditions was a little more than 1 meq/g. The substrate can be regenerated by contact with buffered NH 4Cl at pH 10. The high sodium content of the nickel waste did not prevent sorption of Ni 2+, but it apparently produced an interference with atomic absorption spectrophotometer analyses, giving a spurious reading of 0.8 ppm Ni 2+ when the major nickel line at 232 nm was used for analysis. 相似文献
9.
The photo-electrochemical characterization of the hetero-system CoFe 2O 4/TiO 2 was undertaken for the Ni 2+ reduction under solar light. The spinel CoFe 2O 4 was prepared by nitrate route at 940 °C and the optical gap (1.66 eV) was well matched to the sun spectrum. The flat band potential (-0.21 V SCE) is more cathodic than the potential of Ni 2+/Ni couple (-0.6 V SCE), thus leading to a feasible nickel photoreduction. TiO 2 with a gap of 3.2 eV is used to mediate the electrons transfer. The reaction is achieved in batch configuration and is optimized with respect to Ni 2+ concentration (30 ppm); a reduction percentage of 72% is obtained under sunlight, the Ni 2+ reduction is strongly enhanced and follows a first order kinetic with a rate constant of 4.6×10 -2 min -1 according to the Langmuir-Hinshelwood model. 相似文献
10.
Mg 1−XNi XO solid solution powder samples with different chemical compositions were prepared by heating MgO–NiO mixtures at 1300 °C for 12 h in air. From XRD measurement, all powder samples were indexed as a single phase of cubic structure, of which the diffraction peaks shifted to high-angle side with the increase of doping amount of NiO. The pH values of the solution dispersed with the powder samples decreased when the doping amount of NiO in solid solution was increased. Antibacterial activity of the powder samples was examined by colony count method. In the result, the antibacterial activity of Mg 1−XNi XO was remarkably weaker than original MgO powders, irrespective of the kind of bacteria. In addition, it was found that the antibacterial activity of Mg 1−XNi XO reduced with increasing the doping amount of NiO. Two factors, the generated amount of O 2− and the eluted amount of Ni 2+ ions affected the antibacterial activity of Mg 1−XNi XO solid solution. Especially, the stability of O 2− in aqueous solution is dependent on pH value. Therefore, the strength of antibacterial activity was associated with the pH values in the dispersed solution of Mg 1−XNi XO. 相似文献
11.
The chemical stabilities of modified NiO cathodes doped with 1.5 mol% CoO and 1.5 mol% LiCoO 2 fabricated by a conventional tape casting method were evaluated through the real MCFC single cell operation. The heat-treated samples before oxidation had proper porosities and microstructures for a MCFC cathode. At 150 mA cm −2 in current density, the MCFC single cell using a CoO-doped NiO cathode showed stable cell voltages in the range of 0.833-0.843 V for 1000 h. In contrast, the cell using a LiCoO 2-doped NiO cathode with a maximum of 0.836 V at 500 h degraded to 0.826 V at 1000 h due to a wet seal breakdown at the cathode side. The amounts of nickel precipitated in the electrolytes of the cells using modified NiO cathodes doped with CoO and LiCoO 2 after the operation for 1000 h were 1.2 and 1.4 wt.%, respectively, which were about 60% lower than that of the standard cells using pure NiO cathodes. The enhanced chemical stability of modified NiO cathodes seems to be attributed to the fact that the presence of cobalt increases the lithium content in the cathodes by converting Ni 2+ to Ni 3+, resulting in stabilizing the layered crystal structure. 相似文献
12.
Catalysts based on metals (Pt, Pd) and metal oxides (NiO, Co 3O 4, MoO 3, WO 3), supported on the surface of borate-containing aluminum oxide (B 2O 3–Al 2O 3), in the hydrocracking of sunflower oil at a temperature of 400°C, a pressure 4.0 MPa and a mass hourly space velocity MHSV 5.0 h –1 are compared. H 2 TPR and IR spectroscopy of adsorbed CO and ESDR show that the hydrogenation catalyst components are Pt 0 and Pd 0, a mixture of Ni 2+ + Ni 0, Co 2+ + Co 0, or a mixture of the highest and partially reduced oxides of Mo and W. It is established that catalysts containing Pt, Pd, NiO and Co 3O 4, ensure complete oil hydrodeoxygenation. The main oxygen removal reactions in Ptand Pd-systems are decarboxylation and hydrodecarbonylation. For catalysts with NiO and Co 3O 4, characteristic reactions are reduction and methanation. The highest yield of the diesel fraction was obtained on Pt/B 2O 3-Al 2O 3 catalysts with metal contents of 0.3–1.0 wt %. Along with n-alkanes, the diesel fractions obtained on these catalysts include cycloalkanes and iso-alkanes (up to around 40 wt %) and aromatic hydrocarbons present in trace amounts. Hydrocracking on the Pt system at 400°C for 20 h with MHSV of 1.0 h –1 produces a diesel fraction with a yield of at least 82.0 wt % and the content of iso-alkanes at least 76.1 wt %. 相似文献
13.
The effects of the substitution of V5+ with Ni2+ at the corresponding sites in BiVO4 on the crystal structures, optical properties, and photocatalytic efficiency of BiVO4 was investigated. Ni2+ cations doped at the V5+ sites in BiVO4 was confirmed by X-ray diffraction, Raman, X-ray photoelectron spectroscopy, ultraviolet–visible diffuse reflectance spectra, and photoluminescence spectra. Ni-doped BiVO4 exhibited excellent degradation of crystal violet (CV) compared with the bare BiVO4. For optimal Ni2+ doping of 5%, the degradation rate of CV, which reached about 95% within 180 min of LED light irradiation, was obtained. Ni doping can introduce advantageous defect states that significantly increase the separation and diffusion efficiency of the photo-induced charge carriers, thereby boosting the photocatalytic activity of crystal structures. 相似文献
14.
The reaction-extraction-regeneration system for the liquid-phase oxidation of benzene to phenol in the benzene-water-oxygen system was investigated. Phenol was extracted in the extractor to reduce the concentration of phenol in the benzene phase. As vanadium catalyst was oxidized to inactive species after the oxidation reaction, the regenerator was installed in the system to reduce the oxidation state of vanadium catalyst from V 4+ or VO 2+ to the active V 3+ under H 2 flow. The effects of various operating parameters including concentration of VCl 3 catalyst, O 2 and H 2 flow rates, benzene bubble size, pH, surface area of Pt regeneration catalyst, the metal species, and amount of ascorbic acid were investigated. Ascorbic acid was employed as a reducing agent for helping reduce the V 4+ form to the active form and therefore improving the activity of vanadium catalyst. VCl 3 catalyst concentration of 10 mol/m 3 with pH of 3–4 in the reactor and Pt surface area of 0.05 m 2 in the regenerator showed optimal conditions for the system. 相似文献
15.
Interaction of radiation with glasses often modifies their properties (e.g., the refractive index). Most noticeable is a loss in transmission. Such phenomena can be exploited in photo-sensitive materials, but have to be avoided in other applications. To improve the understanding of defect generation processes, a systematic comparison of defect formation in (fluoride-)phosphate glasses doped with low concentrations of 3d ions was attempted. Samples doped with 10–5000 ppm of Ti, V, Cr, Mn, Fe, Co, or Ni were irradiated in the UV range by excimer lasers. Defects, which generally form in the levels of several ppm, were characterized by optical and by electron spin resonance spectroscopy. V 4+ was photo-oxidized to the empty valence shell d 0 ion. Co 2+, Mn 2+, and Fe 2+ were all photo-oxidized to the trivalent state while Ni 2+ was photo-reduced. The fully oxidized Ti 4+ was also photo-reduced. Cr 3+ showed photo-disproportionation into Cr 2+ and Cr 6+. Qualitative and quantitative changes in defect formation rates depend not only on the ion, but also on the radiation parameters, for example, the wavelength of the excimer lasers used (193, 248, 351 nm) or the initial transmission of the glass samples at the chosen laser wavelength. Defect recovery was followed up to 10 years after the irradiation experiments. 相似文献
16.
This paper investigates the liquid-phase partial oxidation of benzene to phenol in a novel system consisting of reactor, extractor and regenerator. Since vanadium catalyst (V 3+) is oxidized in the reactor and therefore deactivated, the regenerator with Pd or Pt catalyst and H 2 feed is employed to regenerate the deactivated vanadium. The V 4+ ion can be reduced to V 3+ and consequently the phenol production can be enhanced. Although the regenerator can regenerate vanadium catalyst and the reaction can proceed for over 100 h, some V 4+ is still present. The feed position of benzene and catalyst solution have the influence on mixing condition in the reactor and interface area between benzene and catalyst solution. Counter current flow operation with the feeds of catalyst solution and benzene at the top and the bottom respectively shows the highest phenol production. The operating temperature of reactor, extractor and regenerator showed insignificant effect on phenol production rate. 相似文献
17.
Electrical conductivity measurements on EUROCAT V 2O 5–WO 3/TiO 2 catalyst and on its precursor without vanadia were performed at 300°C under pure oxygen to characterize the samples, under NO and under NH 3 to determine the mode of reactivity of these reactants and under two reaction mixtures ((i) 2000 ppm NO + 2000 ppm NH 3 without O 2, and (ii) 2000 ppm NO + 2000 ppm NH 3 + 500 ppm O 2) to put in evidence redox processes in SCR deNO x reaction.It was first demonstrated that titania support contains certain amounts of dissolved W 6+ and V 5+ ions, whose dissolution in the lattice of titania creates an n-type doping effect. Electrical conductivity revealed that the so-called reference pure titania monolith was highly doped by heterovalent cations whose valency was higher than +4. Subsequent chemical analyses revealed that so-called pure titania reference catalyst was actually the WO 3/TiO 2 precursor of V 2O 5–WO 3/TiO 2 EUROCAT catalyst. It contained an average amount of 0.37 at.% W 6+dissolved in titania, i.e. 1.07 × 10 20 W 6+ cations dissolved/cm 3 of titania. For the fresh catalyst, the mean amounts of W 6+ and V 5+ ions dissolved in titania were found to be equal to 1.07 × 10 20 and 4.47 × 10 20 cm −3, respectively. For the used catalyst, the mean amounts of W 6+ and V 5+ ions dissolved were found to be equal to 1.07 × 10 20 and 7.42 × 10 20 cm −3, respectively. Since fresh and used catalysts have similar compositions and similar catalytic behaviours, the only manifestation of ageing was a supplementary progressive dissolution of 2.9 × 10 20 additional V 5+ cations in titania.After a prompt removal of oxygen, it appeared that NO alone has an electron acceptor character, linked to its possible ionosorption as NO − and to the filling of anionic vacancies, mostly present on vanadia. Ammonia had a strong reducing behaviour with the formation of singly ionized vacancies. A subsequent introduction of NO indicated a donor character of this molecule, in opposition to its first adsorption. This was ascribed to its reaction with previously adsorbed ammonia strongly bound to acidic sites. Under NO + NH 3 reaction mixture in the absence of oxygen, the increase of electrical conductivity was ascribed to the formation of anionic vacancies, mainly on vanadia, created by dehydroxylation and dehydration of the surface. These anionic vacancies were initially subsequently filled by the oxygen atom of NO. N o atoms, resulting from the dissociation of NO and from ammonia dehydrogenation, recombined into dinitrogen molecules. The reaction corresponded to . In the presence of oxygen, NO did not exhibit anymore its electron acceptor character, since the filling of anionic vacancies was performed by oxygen from the gas phase. NO reacted directly with ammonia strongly bound on acidic sites. A tentative redox mechanism was proposed for both cases. 相似文献
18.
A new CoMo catalyst for selective hydrotreating of FCC gasoline has been developed; the catalyst is intended for the production of hydrotreated gasoline with up to 10 ppm of sulfur and with a research octane number decreased by less than 1.0. The new catalyst allows hydrotreating of FCC gasoline without its preliminary separation into the light and heavy fractions. The hydrotreating conditions were as follows: hourly space velocity 2.2 h –1, temperature 270°C, pressure 2.5 MPa, H 2/feed = 150 m 3/m 3. The high degree of hydrodesulfurization at minimum decrease in the octane number is achieved due to the high activity of the developed catalyst in hydrodesulfurization of the sulfur-containing components of the feedstock and conversion of reactive high-octane olefins of FCC gasoline into less reactive derivatives with high octane numbers. The catalyst is a CoMoS phase deposited on a support containing amorphous aluminosilicate and γ-Al 2O 3. The method for the preparation of the catalyst is adapted to the equipment of Russian plants and feedstocks. The parameters of hydrotreating using this catalyst ensure the hydrotreating of FCC gasoline to a residual sulfur content of less than 10 ppm with minimum redesign of the equipment currently available at Russian refineries. 相似文献
19.
A series of nickel, molybdenum, and tungsten metal phosphides deposited on a carbon black support (Ni 2P/C, MoP/C, and WP/C) were synthesized by means of temperature-programmed reduction. The samples were characterized by BET surface area, CO uptake, X-ray diffraction (XRD), elemental analysis, and extended X-ray absorption fine structure (EXAFS) measurements. The activity of these catalysts was measured at 613 K and 3.1 MPa in a three-phase, packed-bed reactor for hydrodesulfurization (HDS) and hydrodenitrogenation (HDN) with a model liquid feed containing 500 ppm sulfur as 4,6-dimethyldibenzothiophene (4,6-DMDBT), 3000 ppm sulfur as dimethyl disulfide, and 200 ppm nitrogen as quinoline. The Ni 2P/C catalyst was found to exhibit the best hydroprocessing performance based on equal CO chemisorption sites (70 μmol) loaded in the reactor. An optimum Ni loading for HDS and HDN activity was found as 1.656 mmol g −1 (11.0 wt.% Ni 2P) which gave an HDS conversion of 99% and an HDN conversion of 100% at a molar space velocity of 0.88 h −1. These were much higher than those of a commercial Ni-Mo-S/γ-Al 2O 3 catalyst which gave an HDS conversion of 68% and an HDN conversion of 94%, and a previously reported best Ni 2P/SiO 2 catalyst which gave an HDS conversion of 76% and an HDN conversion of 92%. The use of carbon instead of silica as a support gave rise to other differences, which included smaller particle size, higher CO uptake, lessened retention of P on the support, and reduced sulfur deposition. The stability of the 11.0 wt.% Ni 2P/C catalyst was also excellent with no deactivation observed over 110 h of time on stream. The activity and stability of the Ni 2P/C catalyst were affected by the phosphorous content, both reaching a maximum with an initial Ni/P ratio of 1/2. EXAFS and elemental analysis of the spent samples indicated the formation of a surface phosphosulfide phase on the Ni 2P, which was beneficial for hydrotreating activity, while the bulk structure of the phosphides was maintained during the course of reaction as revealed from the XRD patterns. 相似文献
20.
The catalytic effects of nickel and iron deposited on an FCC (fluidized catalytic cracking) catalyst via metal naphthenates were studied in a micro activity test (MAT) unit after both oxidative and reductive treatments of the catalyst samples.The dehydrogenation activity of nickel was found to be close to the dehydrogenation activity of vanadium – and not several times higher than that of vanadium as is often reported – when deposited on the commercial FCC catalyst used in this study followed by steam deactivation (oxidative treatment) at 760 °C. However, the dehydrogenation activity of nickel was significantly intensified after post-treatment with a CO/N 2 mixture at this temperature (reductive treatment).The results show that iron did not have a dehydrogenation activity after steaming, but had a significant dehydrogenation activity after steaming when followed by exposure to the CO/N 2 mixture at 760 °C. The results indicate that the presence of deposited iron was inducing an additional catalytic cracking activity for the FCC catalyst.It was observed that co-impregnation of equal loadings of nickel, iron and vanadium on the FCC catalyst led to a considerably higher dehydrogenation activity than could be expected from the catalytic behaviour of the separate elements. The dehydrogenation activity was however slightly reduced by the reductive treatment as the reduced dehydrogenation activity from the lower oxidation state of vanadium (V 3+) more than compensated the increased dehydrogenation activity of iron and nickel. A slightly increased gasoline production after the reductive treatment of the co-impregnated sample was a result of the increased production of gasoline from the FCC catalyst itself, which more than compensated for the reduced gasoline production from nickel. 相似文献
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