Ni Acetylacetonate Research Articles

One-Pot Pyrolysis Method to Fabricate Carbon Nanotube Supported Ni Single-Atom Catalysts with Ultrahigh Loading

The practical application of single atom catalysts (SACs) is constrained by the low achievable loading of single metal atoms. Here, nickel SACs stabilized on a nitrogen-doped carbon nanotube structure (NiSA-N-CNT) with ultrahigh Ni atomic loading up to 20.3 wt % have been successfully synthesized using a new one-pot pyrolysis method employing Ni acetylacetonate (Ni(acac)2) and dicyandiamide (DCD) as precursors. The yield and formation of NiSA-N-CNT depends strongly on the Ni(acac)2/DCD ratio and annealing temperature. Pyrolysis at 350 and 650 °C led to the formation of Ni single atom dispersed melem and graphitic carbon nitride (Ni-melem and Ni-g-C3N4). Transition from a stacked and layered Ni-g-C3N4 structure to a bamboo-shaped tubular NiSA-N-CNT structure most likely occurs via a solid-to-solid curling or rolling-up mechanism, thermally activated at temperatures of 700–900 °C. Extended X-ray absorption fine structure (EXAFS) experiments and simulations show that Ni single atoms are stabilized in the N-CNT structure through nitrogen coordination, forming a structure with four nearest N coordination shell surrounded by two carbon shells, Ni–N4. The NiSA-N-CNT catalysts show an excellent activity and selectivity for the electrochemical reduction of CO2, achieving a turnover frequency (TOF) of 11.7 s–1 at −0.55 V (vs RHE), but a low activity for the O2 reduction and O2 evolution reactions, as compared to Ni nanoparticles supported on N-CNTs.

A comparative study of alumina-supported Ni catalysts prepared by photodeposition and impregnation methods on the catalytic ozonation of 2,4-dichlorophenoxyacetic acid

The heterogeneous catalytic ozonation on unsupported and supported oxides has been successfully tested for the removal of several refractory compounds in aqueous solution. In this work, alumina-supported nickel catalysts prepared by photodeposition and impregnation methods were compared in the catalytic ozonation of 2,4-dichlorophenoxyacetic acid (2,4-D). The catalysts were characterized by high-resolution electron microscopy and X-ray photoelectron spectroscopy. The photochemical decomposition of Ni acetylacetonate to produce Ni(OH)2, NiO, and traces of Ni° deposited on alumina was achieved in the presence of benzophenone as a sensitizer. A similar surface composition was found with the impregnated catalyst after its reduction with hydrogen at 500 °C and exposed to ambient air. Results indicated a higher initial activity and maleic acid (byproduct) concentration with the photodeposited catalyst (1 wt% Ni) compared to the impregnated catalyst (3 wt% Ni). These findings suggest the use of the photodeposition method as a simple and reliable procedure for the preparation of supported metal oxide/metal catalysts under mild operating conditions.

Self-organization of nickel nanoparticles dispersed in acetone: From separate nanoparticles to three-dimensional superstructures

Sonochemical synthesis of monodisperse nickel nanoparticles (Ni-NPs) by reduction of Ni acetylacetonate in the presence of polyvinylpyrrolidone stabilizer is reported. The Ni-NPs size is readily controlled to 5 nanometer diameter with a standard deviation of less than 5%. The as-prepared Ni-NPs sample was dispersed in acetone, for 4weeks. For structural analysis was not applied to a magnetic field or heat treatment as key methods to direct the assembly. The transition from separate Ni-NPs into self-organization of three dimensions (3D) superstructures was studied by electron microscopy. Experimental analysis suggests that the translation and rotation movement of the Ni-NPs are governed by magnetic frustration which promotes the formation of different geometric arrangements in two dimensions (2D). The formation of 3D superstructures is confirmed from scanning electron microscopy revealing a layered domain that consists of staking of several monolayers having multiple well-defined supercrystalline domains, enabling their use for optical, electronic and sensor applications.

Effect of Particle Size on the Magnetic Properties of Ni Nanoparticles Synthesized with Trioctylphosphine as the Capping Agent.

Magnetic cores of passive components are required to have low hysteresis loss, which is dependent on the coercive force. Since it is well known that the coercive force becomes zero at the superparamagnetic regime below a certain critical size, we attempted to synthesize Ni nanoparticles in a size-controlled fashion and investigated the effect of particle size on the magnetic properties. Ni nanoparticles were synthesized by the reduction of Ni acetylacetonate in oleylamine at 220 °C with trioctylphosphine (TOP) as the capping agent. An increase in the TOP/Ni ratio resulted in the size decrease. We succeeded in synthesizing superparamagnetic Ni nanoparticles with almost zero coercive force at particle size below 20 nm by the TOP/Ni ratio of 0.8. However, the saturation magnetization values became smaller with decrease in the size. The saturation magnetizations of the Ni nanoparticles without capping layers were calculated based on the assumption that the interior atoms of the nanoparticles were magnetic, whereas the surface-oxidized atoms were non-magnetic. The measured and calculated saturation magnetization values decreased in approximately the same fashion as the TOP/Ni ratio increased, indicating that the decrease could be mainly attributed to increases in the amounts of capping layer and oxidized surface atoms.

Facile synthesis of Pt3Ni alloy nanourchins by temperature modulation and their enhanced electrocatalytic properties

The controlled synthesis of noble metal alloy nanocrystals with anistropic structures is significant for their applications in catalysis, sensing, imaging and biomedicine. This article reports the facile and high-yield synthesis of multi-branched PtNi alloy nanourchins. The synthesis is achieved by the co-reduction of Pt and Ni acetylacetonates through modulating the heating rate of reduction process, which can completely tune the growth kinetics of Pt alloy nanocrystals. Thus obtained PtNi alloy nanourchins exhibit excellent catalytic performance for methanol oxidation and oxygen reduction reactions, which is over 10 times higher than a conventional Pt/C catalyst. In addition, the PtNi alloy nanourchins are highly stable during the long-term operation. It is proposed that the anistropic structure and the alloying effect contribute synergistically to the improvement of catalytic properties. The synthetic strategy is simple, low cost, high yield and up-scalable, which offer a valuable approach to synthesizing metal alloynanocrystals with structural anisotropies, and is promising in designing novel materials for both electrocatalytic and other applications.

Design of a compact ultrahigh vacuum-compatible setup for the analysis of chemical vapor deposition processes.

Optimizing thin film deposition techniques requires contamination-free transfer from the reactor into an ultrahigh vacuum (UHV) chamber for surface science analysis. A very compact, multifunctional Chemical Vapor Deposition (CVD) reactor for direct attachment to any typical UHV system for thin film analysis was designed and built. Besides compactness, fast, easy, and at the same time ultimately clean sample transfer between reactor and UHV was a major goal. It was achieved by a combination of sample manipulation parts, sample heater, and a shutter mechanism designed to fit all into a NW38 Conflat six-ways cross. The present reactor design is versatile to be employed for all commonly employed variants of CVD, including Atomic Layer Deposition. A demonstration of the functionality of the system is provided. First results of the setup (attached to an Omicron Multiprobe x-ray photoelectron spectroscopy system) on the temperature dependence of Pulsed Spray Evaporation-CVD of Ni films from Ni acetylacetonate as the precursor demonstrate the reactor performance and illustrate the importance of clean sample transfer without breaking vacuum in order to obtain unambiguous results on the quality of CVD-grown thin Ni films. The widely applicable design holds promise for future systematic studies of the fundamental processes during chemical vapor deposition or atomic layer deposition.

Novel solvothermal approach to hydrophilic nanoparticles of late transition elements and its evaluation by nanoparticle tracking analysis

Solvothermal treatment of late transition metal acetylacetonates in a novel medium composed either of pure acetophenone or acetophenone mixtures with amino alcohols offers a general approach to uniform hydrophilic metal nanoparticles with high crystallinity and low degree of aggregation. Both pure metal and mixed-metal particles can be accesses by this approach. The produced materials have been characterized by SEM-EDS, TEM, FTIR in the solid state and by Nanoparticle Tracking Analysis in solutions. The chemical mechanisms of the reactions producing nanoparticles has been followed by NMR. Carrying out the process in pure acetophenone produces palladium metal, copper metal with minor impurity of Cu2O, and NiO. The synthesis starting from the mixtures of Pd and Ni acetylacetonates with up to 20 mol% of Pd, renders in minor yield the palladium-based metal alloy along with nickel oxide as the major phase. Even the synthesis starting from a mixed solution of Cu(acac)2 and Ni(acac)2 produces oxides as major products. The situation is improved when aminoalcohols such as 2-aminoethanol or 2-dimethylamino propanol are added to the synthesis medium. The particles in this case contain metallic elements and pairs of individual metals (not metal alloys) when produced from mixed precursor solutions.

Synthesis of Nickel Nanoparticles Supported on Nanoporous Silicon Oxycarbide (SiCO) Sheath−Core Fibers

Nickel (Ni) nanoparticles with average diameters less than 5 nm were successfully synthesized on nanoporous silicon oxycarbide (SiCO) sheath−core fibers by incipient wetness impregnation of Ni acetylacetonate precursor followed by reduction at temperatures above 250 °C. The SiCO fibers were fabricated by pyrolyzing electrospun 5/15 PUS/PMMA composite fibers at temperatures from 250 to 1000 °C to contain nanoporous cores and striated sheaths. The SiCO fibers pyrolyzed up to 600 °C were superhydrophobic and became superhydrophilic when pyrolyzed at 800 °C and above. Such a drastic switch from superhydrophobicity to superhydrophilicity coincided with the disappearance of aliphatic methyl and methylene groups. The SiCO ceramic fibers pyrolyzed at 1000 °C were highly porous with BET surface area 95.7 m2/g, pore volume 0.352 cm3/g, and average pore size 26 nm. They were thermally and chemically stable enough to support the Ni acetylacetonate precursor to be reduced to Ni nanoparticles at 250, 500, and 900 °C. S...

Effects of a 10 T External Magnetic Field on the Thermal Decomposition of Fe, Ni, and Co Acetyl Acetonates

The current investigation is centered on the thermal decomposition (700 degrees C) of acetyl acetonates of Ni, Co, and Fe in a closed reactor that was conducted by employing an external magnetic field (MF) of 10T. Interestingly, reactions of Co and Ni acetyl acetonates under a 10T MF produce Co and Ni nanoparticles (NPs) coated with carbon, while Fe acetyl acetonate produces Fe3O4 uncoated with carbon. Additionally, it is observed that all the as-formed magnetic particles tend to align in one dimension along applied MF; thus, this process can be used to fabricate large arrays of magnetic nanoparticles. The effect of an applied MF to synthesize morphologically and compositionally different products from corresponding precursors with their mesoscopic organization is the key theme of the present paper, explained with a plausible mechanism.

Preparation of zirconia-supported hydrodesulphurisation catalysts by water-assisted spreading

Abstract MoO 3 was deposited over ZrO 2 ( S BET = 108 m 2 g −1 ) and ZrO(OH) 2 ( S BET = 311 m 2 g −1 ) from its aqueous slurry to form saturation adsorption monolayers with densities of 3.2 and 3.5 Mo nm −2 , respectively. Samples were characterised by nitrogen physisorption, X-ray diffraction, and thiophene and benzothiophene hydrodesulphurisation (HDS). The deposited MoO 3 stabilised the high surface area of the amorphous ZrO(OH) 2 after calcination but HDS activity was low. The activity of MoO 3 deposited over monoclinic ZrO 2 was twice as high as that supported on Al 2 O 3 in the reference commercial catalyst BASF M8-30. Furthermore, CoO and NiO were successfully deposited over saturated MoO 3 /ZrO 2 catalyst from aqueous slurries of their low-solubility carbonates and exhibited promotional effects of about 3 and 5, respectively. This deposition resulted in slightly higher HDS activities than obtained with conventional deposition from aqueous solutions of the respective nitrates. Although highest HDS activities over ZrO 2 -supported catalyst were achieved after selective deposition of Co and Ni acetylacetonates onto sulphided Mo samples, activity remained only as high as that of the commercial catalysts CoMo KF 756 and NiMo KF 846 supported on alumina.

Fabrication and Magnetic Properties of Ni Nanospheres Encapsulated in a Fullerene-like Carbon

A very simple, efficient, and economical synthetic technique, which produces fascinating fullerene-like Ni-C (graphitic) core-shell nanostructures at a relatively low temperature, is reported. The thermal dissociation of Ni acetylacetonate is carried out in a closed vessel cell (Swagelok) that was heated at 700 degrees C for 3 h. The encapsulation of ferromagnetic Ni nanospheres into the onion structured graphitic layers is obtained in a one-stage, single precursor reaction, without a catalyst, that possesses interesting magnetic properties. The magnetoresistance (MR) property of Ni nanospheres encapsulated in a fullerene-like carbon was measured, which shows large negative MR, of the order of 10%. The proposed mechanism for the formation of the Ni-C core-shell system is based on the segregation and the surface flux formed in the Ni and carbon particles during the reaction under autogenic pressure at elevated temperature.

Screening of Pd and Ni supported on sol–gel derived oxides for dichloromethane hydrodechlorination

Abstract Several alumina, titania, zirconia and silica xerogels modified with approximately 0.05 wt.% Pd or 0.05 wt.% Ni were synthesized by cogellation and conventional impregnation method using Pd and Ni acetylacetonate as metal precursors. Thermolysis of supported complexes was conducted in static air at 300 and 350 °C for Pd and Ni loaded samples, respectively. The resulting catalysts were characterized by XRD, XRF, BET, TPR, and tested in the vapor phase hydrodechlorination of dichloromethane (DCM) with molecular hydrogen. Prior to reaction, catalysts were reduced at 300 °C in 5% H 2 /He. The synthetic mixture consisted of 1200 ppm CH 2 Cl 2 , 1.2% H 2 and balance He at a space velocity of 0.005 g min ml −1 . Palladium supported catalysts were more active than those containing nickel, i.e. DCM conversions at 200 °C over Pd(I)–Al 2 O 3 almost doubled those obtained over Ni(I)–Al 2 O 3 and no intermediate reaction products were observed over Pd supported catalysts whereas CH 3 Cl was formed over nickel catalysts. Comparison of the specific activities of selected catalysts expressed as TOF, indicate that the observed differences in activity are related to the nature of the support and the accessibility of the metal function to the fluid phase, even though textural properties also appear to play a role. The most active catalyst, palladium impregnated on sol–gel titania (Pd(I)–TiO 2 ) had an initial specific activity of 0.36 s −1 but, it strongly deactivated after a 48 h exposure to 1200 ppm DCM or by thermolysis of the Pd precursor in static air at 600 °C. Although palladium impregnated in sol–gel alumina exhibited lower activity it was much more stable than Pd(I)–TiO 2 .

Hydrogenation of Benzene over Alumina-Supported Nickel Catalysts Prepared from Ni(II) Acetylacetonate

Hydrogenation of benzene was used to probe the activity of Ni/Al2O3 catalysts with metal content in the 0.4–3 wt% range prepared with Ni acetylacetonate as a precursor. Average particle sizes in the 1.9–8 nm range were determined from hydrogen chemisorption measurements depending on the nickel content and reduction temperature. A preliminary decomposition of the organic ligands in air at 250°C followed by reduction markedly increased the activity relative to a direct reduction. Treatments at higher temperatures had a detrimental influence on catalyst efficiency. Catalysts reduced at 350–400°C were more active than those reduced at 450°C and above, with the most active catalysts having nickel content of 1 and 1.6%. The dependency of the turnover frequency on particle size suggested that the reaction was structure sensitive for particle sizes below 4 nm and insensitive above this size. The fraction of unreduced nickel also had an effect on the activity. From a tentative comparison of the turnover frequencies (TOF) with values reported in the literature, it may be inferred that Ni(acac)2 is a rather valuable precursor in preparing very efficient and stable catalysts with low nickel content.

Reforming of methane with carbon dioxide over Ni/Al 2O 3 catalysts: Effect of nickel precursor

The catalytic activities of Ni/γ-Al 2O 3 catalysts prepared using different nickel precursor compounds were studied for the reaction of methane reforming with CO 2. It is found that the nickel precursor employed in the catalyst preparation plays an important role. The catalyst based on nickel nitrate exhibited higher catalytic activity and stability over a 24-h test period than the other two catalysts derived from nickel chloride and nickel acetylacetonate. A comprehensive characterisation of the catalysts showed that the weak interaction between Ni particles and γ-Al 2O 3 resulted in more active sites on Ni nitrate-derived Ni/γ-Al 2O 3 catalyst. Coking studies showed that carbon deposition on Ni catalysts derived from inorganic precursors (nitrate and chloride) were more severe than on the organic precursor-derived catalyst. However, the Ni nitrate-derived catalyst was found to have the highest stability (or lowest deactivation rate) mainly due to the active carbon species (–C–C–) of the resulting graphitic structure and their close contact with the metal particles. In contrast, the carbon formed on Ni–AA catalyst (from Ni acetylacetonate) is dominated by inactive –CO–C– species, thus leading to a rapid accumulation of carbon in this catalyst and more severe deactivation.

Combustion CVD of magnesium spinel and nickel spinel

Combustion chemical vapor deposition (combustion CVD) is being developed to deposit magnesium spinel, MgAl 2O 4, and nickel spinel, NiAl 2O 4, onto silica substrates. A possible use of the magnesium spinel is as an overlayer on thermal barrier coatings (TBCs) used in the hot sections of gas turbines. The deposition of nickel spinel is being developed to explore its role in the thermomechanical spallation of TBCs. Combustion CVD uses a flame to provide the heat for the chemical reactions and the medium for the deposition of the ceramic film. Combustion CVD is performed in the open atmosphere and requires relatively little capital investment compared to conventional CVD processes. Precursors of Mg naphthenate and Al acetylacetonate dissolved in toluene were used to successfully deposit MgAl 2O 4 with the face centered cubic spinel crystal lattice. Ni acetylacetonate and Al acetylacetonate, dissolved in toluene, were used to deposit NiAl 2O 4, with the face centered cubic spinel crystal lattice. Total metal ion concentrations in the flammable solutions ranged from 0.002 to 0.004 M. Flame temperatures at the surface of the substrate during deposition were approximately 1100 °C. Dense, nodular films up to 1 μm. thick were produced at deposition rates of 1.2 to 2.0 μm/h. Transmission electron microscopy (TEM) dark-field imaging indicates that projected grain sizes range from 8 nm to 88 nm. Electron diffraction performed with TEM verifies the spinel crystal structure and quantitative EDS shows weight percents of the constituent elements close to the stoichiometric values.

Reaction of nickel, cobalt, and ferric acetylacetonates with aluminum hydroxide

Fe, Co, and Ni acetylacetonates react with boehmite aluminum hydroxide upon its formation in a mother liquor containing aluminum alcoholate with separation of mixed metal-containing complexes from solution.