Ni Atomic Ratio Research Articles

Composition-Dependent Morphostructural Properties of Ni–Cu Oxide Nanoparticles Confined within the Channels of Ordered Mesoporous SBA-15 Silica

NiO and NiO-CuO polycrystalline rodlike nanoparticles were confined and stabilized within the channels of ordered mesoporous SBA-15 silica by a simple and viable approach consisting in incipient wetness impregnation of the calcined support with aqueous solutions of metal nitrates followed by a mild drying step at 25 °C and calcination. As revealed by low- and high-angle XRD, N2 adsorption/desorption, HRTEM/EDXS and H2 TPR analyses, the morphostructural properties of NiO-CuO nanoparticles can be controlled by adjusting their chemical composition, creating the prerequisites to obtain high performance bimetallic catalysts. Experimental evidence by in situ XRD monitoring during the thermoprogrammed reduction indicates that the confined NiO-CuO nanoparticles evolve into thermostable and well-dispersed Ni-Cu heterostructures. The strong Cu-Ni and Ni-support interactions demonstrated by TPR and XPS were put forward to explain the formation of these new bimetallic structures. The optimal Ni-Cu/SBA-15 catalyst (i.e., Cu/(Cu+Ni) atomic ratio of 0.2) proved a greatly enhanced reducibility and H2 chemisorption capacity, and an improved activity in the hydrogenation of cinnamaldehyde, as compared with the monometallic Ni/SBA-15 or Cu/SBA-15 counterparts, which can be associated with the synergism between nickel and copper and high dispersion of active components on the SBA-15 host. The unique structure and controllable properties of both oxidic and metallic forms of Ni-Cu/SBA-15 materials make them very attractive for both fundamental research and practical catalytic applications.

PtNi alloy nanoparticles supported on carbon-doped TiO2 nanotube arrays for photo-assisted methanol oxidation

To develop anode catalysts for photo-assisted direct methanol fuel cell (PDMFC), carbon-doped TiO2 nanotube arrays-supported PtNi alloy nanoparticles with different Pt/Ni atomic ratio (PtNi/C-TiO2NTs) prepared by pulsed electrodeposition method are evaluated as catalysts for photo-assisted methanol oxidation. The cyclic voltammetry (CV) and chronoamperometry results show that the PtNi/C-TiO2NTs prepared at tonPt:tonNi:=10:7 (ton is the current-on time) with a Pt:Ni atomic ratio of 6.1:5.7 presents the highest catalytic activity for methanol oxidation both in the dark and under illumination. In addition, according to the results obtained from the CO stripping voltammetry and electrochemical impedance spectroscopy (EIS) tests, it was found that the light play an accelerative role in the oxidation of methanol on PtNi/C-TiO2NTs under illumination. The effect of illumination which enhancing the catalytic activity of PtNi/C-TiO2NTs are attributed to (1) methanol and the intermediates be oxidized directly on C-TiO2NTs for the light-induced catalytic effect; (2) more abundant oxygen-donating species be produced on C-TiO2NTs in the presence of light; (3) less COads adsorbing on catalysts due to the presence of stronger metal–support interactions between PtNi alloy nanoparticles and C-TiO2NTs under illumination.

The promotional effect of Ni on bimetallic PtNi/C catalysts for glycerol electrooxidation

The electrocatalytic oxidation of glycerol was studied using carbon-supported 20wt.% PtNi (PtNi/C) catalysts, which were prepared with different Pt:Ni atomic ratios from 3:1 to 1:1 using a colloidal method combined with a freeze-drying procedure. The bimetallic PtNi/C catalysts were characterized by various physicochemical analyses, including X-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS), inductively coupled plasma-atomic emission spectroscopy (ICP-AES), and X-ray photoelectron spectroscopy (XPS). Cyclic voltammetry (CV) measurements indicated that the addition of Ni with a Pt catalyst significantly improved the electrocatalytic activity for glycerol electrooxidation. Among the tested catalysts, the Pt2Ni1/C catalyst had approximately 61% higher mass activity than the Pt/C catalyst. Structural modification via lattice parameter change and electronic modification in the unfilled d band states for Pt atoms may kinetically facilitate the electrooxidation of glycerol with an increased exchange current density over the PtNi/C catalysts.

Roles of Nickel Layer Deposition on Surface and Electric Properties of Carbon Fibers

Agency for Defense Development, Daejeon 305-600, KoreaReceived October 1, 2011, Accepted March 28, 2011Electroless plating of metallic nickel on carbon fiber surfaces was carried out to control specific electricresistivity of the fibers, and the effects of the nickel content and coating thickness on the electric properties werestudied. The structural and surface properties of the carbon fibers were characterized using X-ray diffraction(XRD), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). The specificresistivity of the fibers was measured using a four-point probe testing method. From the XPS results, theoxygen and Ni atomic ratio of the fibers was greatly enhanced as the plating time increased. Additionally, itwas observed that the specific electric resistivity decreased considerably in the presence of metallic nickelparticles and with the formation of nickel layers on carbon fibers.Key Words : Metal plating, Specific resistivity, Carbon fibersIntroductionWith the rapid development of the electronics industry,especially as it pertains to personal computers and mobilesphones, the problem of electromagnetic interference (EMI)is increasing. One effective technique to solve the EMI pro-blem is to increase the electrical conductivity (or decreasespecific electric resistivity) of the plastic cages of electricdevices.

Preparation of PtRuNi/C electrocatalysts by an alcohol-reduction process for electro-oxidation of methanol

PtRuNi/C electrocatalysts with 20 wt% metals loading and Pt:Ru:Ni atomic ratio of 50:40:10 were prepared by an alcohol-reduction process. The electrocatalysts were characterized using energy-dispersive X-ray analysis, X-ray diffraction analysis and thermogravimetric analysis. The electro-oxidation of methanol was studied in sulfuric acid solution by chronoamperometry. It was found that when the initial pH of the reaction medium was acidic, only Pt(IV) and Ru(III) ions were reduced, while the reduction of Ni(II) ions did not take place. Changing the pH of the reaction medium by addition of OH − ions resulted in the reduction of Pt(IV), Ru(III) and Ni(II) ions, which crystallized in the face-centered cubic (fcc) structure. This was observed for OH −/metals ratios ≥6, however, under these conditions the metals loading on the carbon support was only half the nominal value. The PtRuNi/C electrocatalyst prepared with OH −/metals = 6 showed superior performance for methanol oxidation at room temperature compared to commercial PtRu/C electrocatalyst.

Synthesis of Ni-Mo-W Sulfide Nanorods as Catalyst for Hydrodesulfurization of Dibenzothiophene

Two trimetallic sulfurs, MoWNiS and MoWSNi, were synthesized to be used as a catalyst in hydrodesulfurization reactions. The mixed oxide mesoporous nanostructured MoO3 -WO3 with an Mo:W atomic ratio of 1:1 was used as the precursor. The first catalyst was prepared by impregnating nickel in the oxide precursor and then subsequent sulfiding with an H2S/H2 mix at 400 degrees C for 2 hours. The second catalyst was prepared by sulfiding the precursor and then impregnating the nickel, and finally reducing the material with a H2/N2 at 350 degrees C. In both catalysts the Mo:W:Ni atomic ratio was maintained at 1:1:0.5. The materials obtained were characterized by physical adsorption of nitrogen, X-ray diffraction, scanning electron microscopy, transmission electron microscopy. Furthermore, the materials obtained were evaluated by a dibenzothiophene hydrodesulfuration reaction. The diffraction patterns show that both materials are polycrystalline and mainly of MoS2 and WS2 phases.

Preparation of nickel nanoparticles and their catalytic activity in the cracking of methane

Metallic nickel nanoparticles are excellent catalysts for the cracking of methane into carbon nanotubes and hydrogen. Decomposition of tetrahydrate nickel acetate proceeds readily in inert or hydrocarbon streams to produce metallic nickel agglomerates (average size of 10–80nm) at around 350°C. In the present study, this parent salt is thermally treated in methane streams in situ in a thermogravimetric analyzer (TGA), and weight changes corresponding to the carbon buildup in the metallic nickel particles are analyzed to provide some insight into the nickel-catalyzed cracking process. C to Ni atomic ratios (C∕Ni) estimated directly from TGA data provided a systematic approach to study the catalytic activity of the nickel nanoparticles. Methane cracking starts at temperatures as low as 400°C and continues efficiently until approximately 600°C. Between 600 and 660°C, methane decomposition momentarily breaks off, while presumably the catalytic system undergoes a self-reorganization. Cracking resumes at 660°C and continues slowly up to 950°C. The amount of carbon deposited in the 600–660°C interval shows a linear dependence with methane concentrations, with C∕Ni ratios ranging from 6 to 31. Transmission-electron microscopy images of the different C∕Ni residues collected at 660°C show, that during cracking, narrower carbon nanotubes are produced at elevated methane concentrations, suggesting dispersion of nickel nanoparticles.

Isomerization of eugenol and alkenyl aromatics of perfumery interest over Ni-containing layered double hydroxides as solid base catalysts

Isomerization of eugenol was carried out over M(II)Al binary hydrotalcites where M(II) = Mg, Ni, Cu, Li or Co with M(II)/Al atomic ratio of 3.0. All samples were synthesized by coprecipitation under low supersaturation and characterized by powder X-ray diffraction (PXRD), FT-IR, thermogravimetry and BET N 2 adsorption measurements. All samples showed PXRD profiles similar to HT-like phase except for copper, which showed additional reflections of impurity phases. Among the catalysts studied, NiAl3-HT offered maximum conversion of eugenol to isoeugenol of around 77% at 200 °C in 6 h using DMF as solvent. CuNiAl ternary hydrotalcites with (Cu + Ni)/Al atomic ratio of 3.0 with varying Cu:Ni atomic ratios were synthesized and tested for isomerization of eugenol. Addition of copper in NiAl HT-like lattice significantly reduced the isomerization activity wherein 25% substitution of Cu 2+ for Ni 2+ completely annihilated the activity. To study, the influence of synthesis methodology, NiAl3-HT was also synthesized through urea and hexamine hydrolysis wherein sample prepared by former method offered maximum crystallinity among all samples synthesized. However, no isomerization of eugenol was seen for these samples except for the sample obtained through coprecipitation. The observed activity trends could reasonably be correlated with the basicity of the catalysts obtained using phenol adsorption measurements. The catalyst could be reused for two times without much decrease in the activity while further reuse resulted in decrease in the activity. The versatility of the catalyst was checked through isomerization of various alkenyl aromatics wherein at 160 °C, allyl benzene showed maximum conversion to β-methyl styrene and eugenol showed minimum conversion.

Methanol oxidation on carbon-supported Pt–Ru–Ni ternary nanoparticle electrocatalysts

Methanol oxidation on carbon-supported Pt–Ru–Ni ternary alloy nanoparticles was investigated based on the porous thin-film electrode technique and compared with that on Johnson–Matthey Pt–Ru alloy catalyst. Emphasis is placed on the effect of alloying degree on the electrocatalytic activity and stability of the ternary catalysts. The as-prepared Pt–Ru–Ni nanoparticles exhibited a single phase fcc disordered structure, and a typical TEM image indicates that the mean diameter is ca. 2.2 nm, with a narrow particle size distribution. Also, the as prepared Pt–Ru–Ni catalysts exhibited significantly enhanced electrocatalytic activity and good stability for methanol oxidation in comparison to commercial Pt–Ru catalyst available from Johnson–Matthey. The highest activity of methanol oxidation on Pt–Ru–Ni catalysts was found with a Pt–Ru–Ni atomic ratio of 60:30:10 and at a heat-treatment temperature of ca. 175 °C. The significantly enhanced catalytic activity for methanol oxidation is attributed to the high dispersion of the ternary catalyst, to the role of Ni as a promotion agent, and especially to the presence of hydroxyl Ru oxide. Moreover, the stability of the ternary nanocatalytic system was found to be greatly improved at heat-treatment temperatures higher than ca. 250 °C, likely due to a higher alloying degree at such temperatures for the ternary catalysts.

P-type semiconducting Cu2O–NiO thin films prepared by magnetron sputtering

P-type semiconducting thin films consisting of a new multicomponent oxide composed of Cu2O and NiO were deposited on glass substrates by r.f. magnetron sputtering using Cu2O–NiO mixed powder targets. The multicomponent oxide thin films deposited in an Ar atmosphere with a Ni content (Ni/(Cu + Ni) atomic ratio) in the range from 0 to 100 at.% were found to be p-type semiconductors. As the Ni content was increased in the range from 0 to about 30 at.%, the energy bandgap of the resulting films gradually increased as well as the obtained resistivity increased from 70 to 4 × 104 Ω cm, a consequence of decreases in both the Hall mobility and the hole concentration. The films prepared with a Ni content of about 30–50 at.% exhibited a relatively constant resistivity and energy bandgap. The resistivity and the energy bandgap of films prepared with a Ni content above about 60 at.% considerably increased as the Ni content was increased. Furthermore, a pn thin-film heterojunction prepared by depositing undoped n-ZnO and p-multicomponent oxide (Ni content of 50 at.%) thin films exhibited a rectifying I–V characteristic.

Aqueous-phase reforming of ethylene glycol over supported Pt and Pd bimetallic catalysts

More than 130 Pt and Pd bimetallic catalysts were screened for hydrogen production by aqueous-phase reforming (APR) of ethylene glycol solutions using a high-throughput reactor. Promising catalysts were characterized by CO chemisorption and tested further in a fixed bed reactor. Bimetallic PtNi, PtCo, PtFe and PdFe catalysts were significantly more active per gram of catalyst and had higher turnover frequencies for hydrogen production (TOFH2) than monometallic Pt and Pd catalysts. The PtNi/Al2O3 and PtCo/Al2O3 catalysts, with Pt to Co or Ni atomic ratios ranging from 1:1 to 1:9, had TOFH2 values (based on CO chemisorption uptake) equal to 2.8–5.2min−1 at 483K for APR of ethylene glycol solutions, compared to 1.9min−1 for Pt/Al2O3 under similar reaction conditions. A Pt1Fe9/Al2O3 catalyst showed TOFH2 values of 0.3–4.3min−1 at 453–483K, about three times higher than Pt/Al2O3 under identical reaction conditions. A Pd1Fe9/Al2O3 catalyst had values of TOFH2 equal to 1.4 and 4.3min−1 at temperatures of 453 and 483K, respectively, and these values are 39–46 times higher than Pd/Al2O3 at the same reaction conditions. Catalysts consisting of Pd supported on high surface area Fe2O3 (Nanocat) showed the highest turnover frequencies for H2 production among those catalysts tested, with values of TOFH2 equal to 14.6, 39.1 and 60.1min−1 at temperatures of 453, 483 and 498K, respectively. These results suggest that the activity of Pt-based catalysts for APR can be increased by alloying Pt with a metal (Ni or Co) that decreases the strengths with which CO and hydrogen interact with the surface (because these species inhibit the reaction), thereby increasing the fraction of catalytic sites available for reaction with ethylene glycol. The activity of Pd-based catalysts for APR can be increased by adding a water-gas shift promoter (e.g. Fe2O3).

Preparation of ZnNiMo/γ-alumina catalysts from recycled Ni for hydrotreating reactions

Ni, recovered from Ni–Cd cellular phone batteries, was used in the preparation of ZnNiMo/Al 2O 3 catalysts. The catalysts were characterized by temperature programmed reductions (TPR), surface area determinations (BET) and chemical analysis. Vanadyl octaethyl porphyrin (VOOEP) hydrodeporphyrinization (HDP) and thiophene hydrodesulfurization (HDS) were used as catalytic tests. It was found that the addition of Zn increases the ratio between octahedral and tetrahedral Mo in ZnMo and ZnNiMo catalysts, and that Ni addition lowers the reduction temperature of Mo species. Both results induce a positive synergetic effect for HDP and HDS reactions. An activity maximum was found for the catalyst with a Zn/(Zn + Ni) atomic ratio equal to 0.29, for both reactions. Finally, the use of a possible pollutant (Ni–Cd batteries) to produce a catalyst to eliminate contaminants in fuels was shown to be feasible.

Carbon-Supported Pt-Ni Alloys Prepared by the Borohydride Method as Electrocatalysts for DMFCs

Carbon-supported Pt-Ni electrocatalysts in the Pt:Ni atomic ratio 90:10 and 70:30 were prepared by reduction at room temperature of Pt and Ni salts with sodium borohydride and tested for the first time in direct methanol fuel cells ~DMFCs! both as anode and as cathode materials. The performance of Pt-Ni as cathode in DMFC was higher than that of Pt-Ni as anode. Pt90Ni10 as cathode showed better performance than Pt both in terms of mass activity and specific activity. When used as an anode material, the cell performance increased with increasing nickel content in the material. The enhanced performance of Pt-Ni as a cathode is ascribed both to a better activity for the oxygen reduction ~electronic effect! and a better methanol-tolerance ~ensemble effect! than Pt, related mainly to the alloyed nickel, while the improvement of Pt-Ni as anode for methanol oxidation is attributed to the presence of nonalloyed NiO species. © 2005 The Electrochemical Society. @DOI: 10.1149/1.1870632# All rights reserved.

Optical properties of sol–gel SiO 2 films containing nickel

SiO 2 films containing nickel were prepared using the sol–gel method with nominal Si to Ni atomic ratios of 1.2, 3.1 and 7.1. After thermal annealing under different conditions, the optical properties of the films were studied using optical reflectance and transmittance measurements. It was found that samples annealed in air at 500 °C show an absorption band at wavelengths of about 440 nm associated with Ni 2+ ions in octahedral positions. In addition, in films with Si to Ni atomic ratios of 1.2 and 3.1, there is an absorption edge at short wavelengths, indicating the formation of NiO nanosized particles. Samples with a Si to Ni atomic ratio of 1.2 were also heat-treated in a H 2/N 2 atmosphere at 500 and 800 °C, producing metallic Ni nanoparticles embedded in the vitreous matrix. The effective dielectric function of both NiO–SiO 2 and Ni–SiO 2 composite films was modeled with the Maxwell–Garnett expression. X-ray diffraction measurements confirm the presence of NiO and Ni nanoparticles in the films.

Synergistic effect in the hydroxylation of phenol over CoNiAl ternary hydrotalcites

Hydroxylation of phenol was carried out over a series of CoNiAl ternary hydrotalcites (HTs) having a (Co+Ni)/Al atomic ratio close to 2.6 and a Co:Ni atomic ratios ranging from 1:0 to 0:1 using H 2O 2 as oxidant and water as solvent. Both end members of this series, namely CoAl-HT and NiAl-HT, showed negligible conversion of phenol, while cooperative catalytic behavior was noted when both elements were present together. However, activity of the catalysts varied with Co/Ni atomic composition, wherein the activity decreased with a decrease in the concentration of cobalt. A variation in the activity with the crystallinity of the materials was noted wherein a highly ordered material showed maximum activity and dropped with a decrease in the orderliness of the layered structure. Temperature-programmed reduction (TPR) of the fresh samples substantiated the activity trend by exhibiting a decrease in the reduction maximum with a decrease in the concentration of cobalt. Probably an optimal configuration of sites involving cobalt, nickel, and Brønsted basic hydroxyl groups is necessary for promoting the reaction. Among the catalysts studied, catalyst with a Co/Ni atomic ratio of 1:5 showed maximum conversion of phenol (14.2%, substrate:oxidant=2:1, 65 °C) with a catechol/hydroquinone ratio of 3.8. Heating of these samples even at slightly elevated temperatures (>120 °C in air for 5 h) led to complete loss in the activity necessitating the requirement of a well-ordered network. Prior to catalytic studies, the samples were characterized by various physicochemical techniques for structure–activity relationships.

Interactions at the Ni3Al(111)−S−Al2O3 Interface at Elevated Temperatures: Ordering of Al2O3 on an S-Modified Substrate

Auger electron spectroscopy (AES), low-energy electron diffraction (LEED), and scanning tunneling microscopy (STM) have been used to investigate the growth, morphology, and thermal stability of the oxide prepared on a (2 × 2)-S-covered Ni3Al(111) surface. The results demonstrate that although sulfur significantly alters the oxidation rate and oxide morphology on the Ni3Al(111) substrate at room temperature, it does not inhibit the formation of the ordered γ‘-Al2O3 at elevated temperatures. The oxide formed on the S-modified Ni3Al(111) surface at room temperature is stable up to at least 1100 K. Sulfur remains at the oxide−Ni3Al(111) interface during oxygen exposure at ∼300 K. During annealing, however, sulfur is removed from the oxide−alloy interface. Annealing from 300 to 1100 K results in the segregation of aluminum to the oxide−alloy interface, as evidenced by an enhancement in the Al(1396)/Ni(848) atomic ratio, and the appearance of a metallic aluminum peak in the Auger spectra.

Laser purification of metals (II); Purification of Ni and Ag

We report on our effort in laser purification of metals and discuss the limitations of the method. Vaporized atoms are photoionized through a three-step excitation to the continuum above the ionization level and extracted by an electric field. The species so far tested are alloys of Ag and Ni. For purification of Ag, starting with an alloy system Ag 0.90In 0.10, we observed only a reduction of the In (Ag+In) atomic ratio of 0.10 in the vapor phase to 0.054. For Ni, using Ni 0.60Cu 0.40 as the starting material, we could reduce the Cu (Cu+Ni) atomic ratio of 0.63 in the vapor phase to 0.065 after laser purification. For both systems the main factor limiting the level of purification is considered to be a concomitant deposition of unionized impurity atoms that are scattered away from the atomic beam to the substrate.

Preparation of Al–Ni alloy films by alternate sputter deposition

Al‐Ni alloy films with an Al to Ni atomic ratio greater than 0.79 were prepared via an alternate sputter deposition technique. The formation of the alloy films was attributed to the interdiffusion and reaction between Al and Ni atoms by the adatom substitution. The crystal structures are all in accordance with the equilibrium phase diagram when the Al to Ni atomic ratio is greater than 2.30. The film with Al to Ni atomic ratio 2.30 is composed of Ni2Al3 and NiAl. A complete NiAl film was obtained when the Al to Ni atomic ratio is less than 1.53. The crystal structure of the film was reverted to Ni–Al equilibrium phases when the −100 V substrate bias was applied during deposition. The films with a NiAl structure showed 〈100〉 and 〈110〉 preferred orientations on the Si and glass substrates, respectively, disregarding the application of bias. The application of substrate bias significantly reduced the O and N contents and prevented the Al from oxidization. However, bias caused an incorporation of Ar and a low...

Relation between hydrodesulfurization activity and the state of promoters in precursor calcined [formula omitted] catalysts

Two series of NiCoMo Al 2O 3 hydrodesulfurization (HDS) catalysts prepared by different procedures were investigated. In each series the Mo loading and the total content of promoters (Co + Ni) were kept constant but the Co (Co + Ni) atomic ratio was varied from 0 to 1. The two series of catalysts were prepared by a sequential wet impregnation technique. In series I, the impregnations of both Mo and promoters were carried out at the pH of the impregnating aqueous solutions, employing an intermediate calcination; in series II, Mo was impregnated at pH 10, while the promoters were added in aqueous ethanol solutions without intermediate calcination. Catalysts in their calcined state were characterized by reduction in H 2 at 500 °C, O 2 chemisorption, and infrared spectroscopy of adsorbed NO. The HDS activity and the optimum Co (Co + Ni) atomic ratio were different for the two series, in agreement with our previous studies, HDS activity being generally higher for series II than for series I. Dispersion of Mo (as estimated from O 2 chemisorption) and NO adsorption on Mo in reduced catalysts (as judged from the intensity of the band at about 1705 cm −1) were not substantially different for the two series of catalysts and did not correlate with HDS activity. However, adsorbed NO on promoters in oxidized catalysts (bands at about 1880 and 1800 cm −1) followed roughly the same trend as HDS activity, suggesting that the active sites may be related to the Co and Ni atoms adsorbing NO. Possible reasons for the differences between HDS activity of the two series are considered.