XPS study on the vanadocene-magnesium system to understand the hydrogen sorption reaction mechanism under room temperature

Magnesium surface dope with vanadium has been considered as one of the best material for the hydrogen storage application. Optimization of vanadium concentration doping is important to retain the hydrogen storage capacity above 6 wt %. Vanadocene, bis(η5-cyclopentadienyl) vanadium, with the formula V(C₅H₅)₂, commonly abbreviated as Cp₂V is considered as the best precursor for the vanadium to dope the optimized concentration of vanadium over the Mg surface. The vanadium doping over the magnesium has been studied by X-ray photoelectron spectroscopy (XPS) in details. The vanadium doped Mg has been found to be hydrogenated even at 0 °C under nominal hydrogen pressure (above plateau pressure). Besides, the dehydrogenation temperature was also found to be below 200 °C which is remarkable less as compared to pure magnesium, and comparable to the best catalysts for Mg-MgH₂ system reported till date.     

Tailoring the hydrogen absorption desorption's dynamics of MgMgH2 system by titanium suboxide doping

Titanium suboxide (TiO) is one of the best catalysts which improved the hydrogen absorption-desorption property of MgH₂ Mg system. The TiO catalyzed Mg MgH₂ have shown a remarkably reduced apparent activation energy and enhanced the hydrogen absorption-desorption kinetics. The X-ray photoelectron spectroscopy (XPS) analysis has indicated that the oxidation state of Ti in TiO remains unchanged during ball milling and hydrogen absorption-desorption of TiO-doped-MgH₂. The X-ray diffraction (XRD) analysis further confirms the XPS result. The TiO has shown the excellent catalytic effect on the MgMgH₂ system which remarkably reduced the hydrogen absorption-desorption temperatures.     

A tetranuclear nickel(II) complex for water oxidation: Meeting new challenges

Ni complexes are promising catalysts for water splitting. Herein, a tetranuclear nickel(II) complex with bis-[(E)-N′-(1-(pyridin-2-yl)ethylidene)]carbohydrazide (HL), was synthesized and characterized by spectroscopic methods and single crystal X-ray analysis. The complex is a tetranuclear complex and the ligands are coordinated to the metal ions in the mono-negative form, (L)^- to form a tetranuclear [NiL]₄⁴⁺ unit. Each Ni(II) ion is six-coordinated by pyridine nitrogen, azomethine nitrogen and oxygen atoms of two perpendicular carbohydrazone ligands in the mer configuration. The complex was studied as a water-oxidizing catalyst. In the next step, the role of the Ni-based compound for water oxidation on the surface of fluorine doped tin oxide as one of the true catalysts was investigated by scanning transmission electron microscopy, scanning transmission electron microscopy, spectroelectrochemistry, and electrochemistry. The electrode after water oxidation by the complex was studied and a relation between the decomposition of the Ni complex and water-oxidation reaction was proposed. The experiments show that under water-oxidation condition in the presence of the complex, a Ni-based compound on the electrode is a candidate as a contributor to the observed catalysis.     

Study on the thermal decomposition of NaBH4 catalyzed by ZrCl4

The catalytic effect of zirconium tetrachloride (ZrCl₄) on the thermal dehydrogenation of NaBH₄ has been studied. The ZrCl₄ reduced to ZrCl₂ and metallic zirconium which exhibit the high catalytic activity during thermal dehydrogenation. The activation energy corresponding to dehydrogenation of NaBH₄ is remarkably reduced to 180 kJ/mol in the presence of a catalyst as compared to pure-NaBH₄ which was found to be 275 kJ/mol under the similar experimental conditions. The reduced activation energy leads to decreased onset dehydrogenation temperature (<300 °C). A substantial amount of sodium remained at the end of the dehydrogenation of catalyzed sample. The low-temperature dehydrogenation of catalyzed NaBH₄ could be useful to manage the evaporation of sodium metal.     

Synergic effect of vanadium trichloride on the reversible hydrogen storage performance of the MgMgH2 system

Vanadium trichloride (VCl₃) is one of the best catalysts for the hydrogenation-dehydrogenation MgMgH₂ system. X-ray photoelectron spectroscopy (XPS) has shown that VCl₃ reduced to metallic vanadium during ball milling along with MgH₂. The in-situ-formed metallic vanadium doped over the MgH₂ surface which has shown an excellent catalytic effect on hydrogenation-dehydrogenation of the MgMgH₂ system. The catalyzed surface reduced the activation energies of hydrogenation-dehydrogenation reactions and correspondingly on-set hydrogenation-dehydrogenation temperatures. The microstructural analysis has also shown an excellent grain refinement property of VCl₃ which reduced the crystallite size of MgH₂. The decreased crystallite size decreases the diffusion path length of hydrogen and increases the active surface area which eventually enhances the hydrogenation-dehydrogenation kinetics of MgMgH₂.     

Influence of impregnated iron and nickel on the pyrolysis of cellulose

In this work, we prepared iron- or nickel-impregnated cellulose to examine the influence of the metal on the yield and composition of fast pyrolysis products. In order to identify the mechanisms promoted during the catalytic conversion, pyrolysis was investigated using an experimental set-up coupling TG (thermogravimetric) analysis and Micro-GC (Gas Chromatography). The results showed that with relatively low catalyst loading (mass fraction of 1.5% Fe or 1.7% Ni) impregnated metal can catalyze some rearrangement reactions such as dehydration and decarboxylation starting from 180 °C, promoting the char formation and thus inhibiting cellulose depolymerization. As a consequence metal impregnation led to a decrease of tar and CO yields balanced by an increase of char, H₂O and CO₂ yields. Depending on the applied metal, other primary reactions can be specifically catalyzed. In particular, in the presence of nickel TG analysis revealed an important mass loss at temperatures as low as 210 °C and an important increase of H₂ production in the temperature range 400–500 °C. These findings open promising perspectives to optimize the production of fuels and chemicals from biomass.     

Enhancing hydrogen storage properties of the Mg/MgH2 system by the addition of bis(tricyclohexylphosphine)nickel(II) dichloride

This is a first report on the use of the bis(tricyclohexylphosphine)nickel (II) dichloride complex (abbreviated as NiPCy3) into MgH₂ based hydrogen storage systems. Different composites were prepared by planetary ball-milling by doping MgH₂ with (i) free tricyclohexylphosphine (PCy3) without or with nickel nanoparticles, (ii) different NiPCy3 contents (5–20 wt%) and (iii) nickel and iron nanoparticles with/without NiPCy3. The microstructural characterization of these composites before/after dehydrogenation was performed by TGA, XRD, NMR and SEM-EDX. Their hydrogen absorption/desorption kinetics were measured by TPD, DSC and PCT. All MgH₂ composites showed much better dehydrogenation properties than the pure ball-milled MgH₂. The hydrogen absorption/release kinetics of the Mg/MgH₂ system were significantly enhanced by doping with only 5 wt% of NiPCy3 (0.42 wt% Ni); the mixture desorbed H₂ starting at 220 °C and absorbed 6.2 wt% of H₂ in 5 min at 200 °C under 30 bars of hydrogen. This remarkable storage performance was not preserved upon cycling due to the complex decomposition during the dehydrogenation process. The hydrogen storage properties of NiPCy3-MgH₂ were improved and stabilized by the addition of Ni and Fe nanoparticles. The formed system released hydrogen at temperatures below 200 °C, absorbed 4 wt% of H₂ in less than 5 min at 100 °C, and presented good reversible hydriding/dehydriding cycles. A study of the different storage systems leads to the conclusion that the NiPCy3 complex acts by restricting the crystal size growth of Mg/MgH₂, catalyzing the H₂ release, and homogeneously dispersing nickel over the Mg/MgH₂ surface.     

Syntheses of nickel sulfides from 1,2-bis(diphenylphosphino)ethane nickel(II)dithiolates and their application in the oxygen evolution reaction

In this work, four heteroleptic Ni(II)dppe dithiolates complexes, [Ni(NED)(dppe)] (Ni-NED), [Ni(ecda)(dppe)] (Ni-ecda), [Ni(i-mnt)(dppe)] (Ni-i-mnt) and [Ni(cdc)(dppe)] (Ni-cdc) (dppe = 1,2-bis(diphenylphosphino)ethane; NED = 1-nitroethylene-2,2-dithiolate; ecda = 1-ethoxycarbonyl-1-cyanoethyelene-2,2-dithiolate; i-mnt = 1,1-dicyanoethylene-2,2-dithiolate and cdc = cyanodithioimidocarbonate), have been synthesized and characterized by analytical and spectroscopic techniques (Elemental analysis, vibrational, electronic absorption and multinuclear NMR spectroscopy). Structural characterization of all the four complexes by single crystal X-ray diffraction study suggests distortion in regular square planar geometry at Ni(II) center by coordination with two phosphorus of the dppe and two sulfur of the dithiolate ligands, respectively. The decomposition of all four complexes have been done to produce nickel sulfides and the resulting nickel sulfides have been utilized for electrocatalytic oxygen evolution reaction (OER). The nickel sulfide obtained by decomposing Ni-cdc shows best activity with overpotential η = 222 mV at j = 10 mA cm^?2 and a Tafel slope of 44.2 mV dec^?1 while other catalysts shows η > 470 mV at j = 5 mA cm^?2 and η > 600 mV at j = 10 mA cm^?2 at loading of 1.3 mg cm^?2.     

Proton reduction by a Ni(II) catalyst and foot-of-the wave analysis for H2 evolution

A nickel based molecular catalyst [Ni(QCl-tpy)₂]Cl₂·7H₂O (where QCl-tpy = 2-choloro-3-(2,6-di (pyridin-2yl)pyridine-4-yl) quinoline) has been synthesized, characterized by single crystal XRD and other spectroscopic techniques. The complex [Ni^II(QCl-tpy)₂]²⁺ has also been employed for the electrocatalytic proton reduction in DMF/H₂O (95:5 v/v) using trifluoro acetic acid (TFA) as the proton source. It exhibits a reasonably efficient catalytic ability towards proton reduction under organic media. Compared to the parent [Ni^II(tpy)₂]²⁺ during the electro-catalysis, the complex [Ni^II(QCl-tpy)₂]²⁺ behaves as a better catalyst in terms of higher catalytic current and 180 mV of lower overpotential as well. It is expected due to the presence of 2-chloroqinoline moiety in the terpyridine framework. The rate of H₂ evolution was analysed with the use of Foot-of-the Wave Analysis (FOWA) method. The complex shows a TOF of 3.68 s⁻¹ as obtained from Foot-of-the Wave Analysis (FOWA) at the scan rate 100 mVs⁻¹ for 1.0 mM [Ni^II(QCl-tpy)₂]²⁺ complex. The acid base equilibria reveals the dechelation followed by protonation at one of the coordinated pyridine rings of the QCl-tpy ligand. There could be a pendant base effect towards hydrogen evolution due to dechelated pyridine ring of the coordinated QCl-tpy ligand, which acts as a proton relay. Based on the spectroscopic evidence and electrochemical studies a plausible mechanism for the reduction of proton to H₂ has been proposed.     

On the electrochemical and thermal behavior of lithium bis(oxalato)borate (LiBOB) solutions

In recent years, lithium bis(oxalato)borate, LiB(C₂O₄)₂ (LiBOB) has been proposed as an alternative salt to the commonly used electrolyte, LiPF₆. There is evidence of the enhanced stability of Li-ion battery electrodes in solutions of this salt, due to a unique surface chemistry developed in LiBOB solutions. The present study is aimed at further exploring the electrochemical and thermal properties of LiBOB solutions in mixtures of alkyl carbonates with non-active metal, graphite and lithium electrodes. FTIR spectroscopy, XPS, EQCM, in situ AFM imaging, and DSC were used in conjunction with standard electrochemical techniques. The study also included a comparison between LiBOB and LiPF₆ solutions. The development of a favorable surface chemistry in LiBOB solutions that provides better passivation to Li and Li-graphite electrodes was clearly evident.     

Improvement on hydrogen storage thermodynamics and kinetics of the as-milled SmMg11Ni alloy by adding MoS2

In this experiment, the Mg-based hydrogen storage alloys SmMg₁₁Ni and SmMg₁₁Ni + 5 wt.% MoS₂ (named SmMg₁₁Ni-5MoS₂) were prepared by mechanical milling. By comparing the structures and hydrogen storage properties of the two alloys, it could be found that the addition of MoS₂ has brought on a slight change in hydrogen storage thermodynamics, an obvious decrease in hydrogen absorption capacity, an obvious catalytic action on hydrogen desorption reaction, and a lowered onset desorption temperature from 557 to 545 K. Additionally, the addition of MoS₂ could dramatically improve the alloy in its hydrogen absorption and desorption kinetics. To be specific, the hydrogen desorption times of 3 wt.% H₂ at 593, 613, 633 and 653 K were measured to be 1488, 683, 390 and 192 s respectively for the SmMg₁₁Ni alloy, which were reduced to 938, 586, 296 and 140 s for the MoS₂ catalyzed SmMg₁₁Ni alloy at identical conditions. The activation energies of the alloys with and without MoS₂ for hydrogen desorption are 87.89 and 100.31 kJ/mol, respectively. The 12.42 kJ/mol decrease is responsible for the ameliorated hydrogen desorption kinetics by adding catalyst MoS₂.     

Influence of the supports ZrO2 on selective methanation of CO over the nickel supported catalysts

It is attempted to optimize preparation of ZrO₂ as support of the nickel catalysts for selective methanation of CO in H₂-rich gas (CO-SMET). Therefore, the supports ZrO₂ were prepared at first by thermal decomposition method from zirconium oxynitrate and zirconium oxychloride at the calcination temperature of 400 °C and 800 °C, respectively. It is illustrated that the salt kind and calcination temperature affected phase state (tetragonal, monoclinic), crystallite size and specific surface area (SSA) of the supports. The difference in property of the supports influenced catalytic performance of the catalysts Ni/ZrO₂ for CO-SMET reaction. Especially, the chlorine ion residues in the support ZrO₂ prepared from zirconium oxychloride was beneficial for CO removal selectively. Furthermore, a precipitation method was adopted to prepare ZrO₂ for comparison with the thermal decomposition method with use of the zirconium oxychloride as starting material. It is found that the supports ZrO₂ prepared by the precipitation method induced a better dispersion of metallic Ni on its surface. The catalyst Ni/ZrO₂ with use of the support ZrO₂ prepared by the precipitation method and calcination at 400 °C exhibited a good performance at the reaction temperature of 220 °C in the 100 h durability test, where CO outlet concentration was kept below 10 ppm and the selectivity remained constant at 100%. Relation of Ni crystallite size and chlorine ion residues with the catalytic performance was discussed.     

同时催化去除柴油机微粒和NO_x的试验研究(2)

通过在γ Al2O3小球和柴油机微粒过滤器(DPF)上涂覆复合金属氧化物催化剂Cu0.95K0.05Fe2O4和La0.9K0.1CoO3,利用程序升温反应(TPR)技术,对同时催化去除柴油机微粒(PM)和NOx反应进行了试验研究。研究结果表明,La0.9K0.1CoO3催化剂比Cu0.95K0.05Fe2O4催化剂具有更高的同时去除PM—NOx的催化反应活性。在低负荷下,柴油机的PM由于SOF含量多而使NOx降低的幅度比高负荷下的大,其燃烧温度也比高负荷下的低。同时,NO和O2的共存促进了PM的氧化燃烧。另外,PM和催化剂之间"松接触"的催化活性要比"紧接触"低。     

On the effect of yttrium promotion on Ni-layered double hydroxides-derived catalysts for hydrogenation of CO2 to methane

Ni-containing mixed oxides derived from layered double hydroxides with various amounts of yttrium were synthesized by a co-precipitation method at constant pH and then obtained by thermal decomposition. The characterization techniques of XRD, elemental analysis, low-temperature N₂ sorption, H₂-TPR, CO₂-TPD, TGA and TPO were used on the studied catalysts. The catalytic activity of the catalysts was evaluated in the CO₂ methanation reaction performed at atmospheric pressure. The obtained results confirmed the formation of nano-sized mixed oxides after the thermal decomposition of hydrotalcites. The introduction of yttrium to Ni/Mg/Al layered double hydroxides led to a stronger interaction between nickel species and the matrix support and decreased nickel particle size as compared to the yttrium-free catalyst. The modification with Y (0.4 and 2 wt%) had a positive effect on the catalytic performance in the moderate temperature region (250–300 °C), with CO₂ conversion increasing from 16% for MO-0Y to 81% and 40% for MO-0.4Y and MO-2.0Y at 250 °C, respectively. The improved activity may be correlated with the increase of percentage of medium-strength basic sites, the stronger metal-support interaction, as well as decreased crystallite size of metallic nickel. High selectivity towards methane of 99% formation at 250 °C was registered for all the catalysts.     

Synthesis of nickel catalyzed sulfonated poly (phenylenebenzophenone)s from primarily sulfonated monomer for proton exchange membranes

This extensive study adequately explores the considerable influence of nickel catalyst and wholly aromatic primarily sulfonated monomers. The synthesis of the chemically and mechanically stable sulfonated poly (phenylenebenzophenone)s (SPPBP) flexible membranes from primarily Sulfonated 1,4-dichloro-2,5-diphenylenebenzophenone (SPBP) and 1,4-dichloro-2,5-diphenylenemethoxybenzophenone (SPMBP) monomers have been reported here using nickel catalyzed carbon-carbon coupling copolymerization. The synthesized SPBP monomer typically possesses a symmetrical structure with excellent reactivity that effectively assisted to control the position, number, and distribution of the sulfonic acid groups in the polymer backbone and attained high molecular weight SPPBP copolymers. The synthesized polymers showed ion exchange capacity (IEC) 1.0–1.93 meqv./g, water uptake 36.4–84.7% and comparable proton conductivity 28.5–94.9 meqv./g to Nafion^® (98.92 meqv./g) at 90 °C. The atomic force microscopic (AFM) results show that SPPBP copolymer membranes provide well phase-separated morphology and thermogravimetric analysis (TGA) confirms the excellent thermal stability of the synthesized SPPBP membranes as well. The synthesized SPPBP membranes possess a potential feature for the practical application in the fuel cell.     

Sustainable nickel catalyst for the conversion of lignocellulosic biomass to H2-rich gas

The objective of this paper was to design sustainable nickel catalysts supported on selected fly ash based zeolites to thermal processing of lignocellulosic feedstock towards hydrogen-rich gas. Moreover, in order to increase its catalytic performance in the studied process the catalyst supported on the most promising fly ash based zeolite was modified by selected rare-earth and transition metals (La, Pr, Ce, Y, Gd, Zr). The performed measurements exhibited that incorporation of nickel into the structure of zeolite A modified by lanthanum resulted in the most effective production of H₂. The characterization of its physicochemical properties (XRD, TPR, SEM-EDS, TPD-NH₃, BET and TGA-DTA) suggested that large pore size, moderate acidity, increased reducibility of an active phase and higher resistance to coke formation are the main factors responsible for increased activity of this catalyst.     

A new catalyst based on a nickel(II) complex of diiminodiphosphine for hydrogen evolution and oxidation

Based on that hydrogen energy is widely used in fuel cells, we focus our interests on the design and research of new complexes that catalyze the reaction in both directions, such as hydrogen evolution reactions (HERs) and hydrogen oxidation reactions (HORs). A highly efficient catalyst for both hydrogen evolution and oxidation, based on a nickel(II) complex, [Ni-en-P₂](ClO₄)₂, has been designed and provided by the reaction of Ni(ClO₄)₂ with N,N′-bis[o-(diphenylphosphino)benzylidene]ethylenediamine (en-P₂) in our group. Its structure has been determined by X-ray diffraction. [Ni-en-P₂](ClO₄)₂ can electro-catalyze hydrogen evolution both from acetic acid and a neutral buffer (pH 7.0) with a turnover frequency (TOF) of 204 and 1327 mol of hydrogen per mole of catalyst per hour (H₂/mol catalyst/h) under an overpotential (OP) of 914.6 mV and 836.6 mV, respectively. [Ni-en-P₂](ClO₄)₂ also can electro-catalyze hydrogen oxidation with a TOF of 111.7 s⁻¹ under an OP of 330 mV. The results can be attributed to that [Ni^II-en-P₂](ClO₄)₂ has three good reversible redox waves at 1.01 (Ni^III/II), −0.79 (Ni^II/I) and −1.38 V (Ni^I/0) versus Fc^+/0, respectively. We hope these findings can afford a new method for the design of electrocatalysts for both H₂ evolution and H₂ oxidation.     

Hydrogen production by steam reforming of liquefied natural gas (LNG) over nickel catalysts supported on cationic surfactant-templated mesoporous aluminas

Two types of mesoporous γ-aluminas (denoted as A-A and A-S) are prepared by a hydrothermal method under different basic conditions using cationic surfactant (cetyltrimethylammonium bromide, CTAB) as a templating agent. A-A and A-S are synthesized in a medium of ammonia solution and sodium hydroxide solution, respectively. Ni/γ-Al₂O₃ catalysts (Ni/A-A and Ni/A-S) are then prepared by an impregnation method, and are applied to hydrogen production by steam reforming of liquefied natural gas (LNG). The effect of a mesoporous γ-Al₂O₃ support on the catalytic performance of Ni/γ-Al₂O₃ is investigated. The identity of basic solution strongly affects the physical properties of the A-A and A-S supports. The high surface-area of the mesoporous γ-aluminas and the strong metal–support interaction of supported catalysts greatly enhance the dispersion of nickel species on the catalyst surface. The well-developed mesopores of the Ni/A-A and Ni/A-S catalysts prohibit the polymerization of carbon species on the catalyst surface during the reaction. In the steam reforming of LNG, both Ni/A-A and Ni/A-S catalysts give better catalytic performance than the nickel catalyst supported on commercial γ-Al₂O₃ (Ni/A-C). In addition, the Ni/A-A catalyst is superior to the Ni/A-S catalyst. The relatively strong metal–support interaction of Ni/A-A catalyst effectively suppresses the sintering of metallic nickel and the carbon deposition in the steam reforming of LNG. The large pores of the Ni/A-A catalyst also play an important role in enhancing internal mass transfer during the reaction.     

Tuning of active nickel species in MOF-derived nickel catalysts for the control on acetic acid steam reforming and hydrogen production

Acetic acid (AcOH) steam reforming for hydrogen (H₂) generation was investigated using a zero valent nickel complex (Ni-comp) derived from a metal-organic framework precursor supported over aluminum oxide/lanthanum oxide-cerium dioxide (ALC). The effects of Ni loading ratio (10, 15, and 20 wt%) on the catacatalytic activity were investigated in the range of 400 to 650 °C to H₂ generation. The Ni-comp/ALC catalysts exhibited almost complete conversion of AcOH (X_AcOH >98%) to H₂ (X_H2>90%) alongside some impurities (e.g., carbon monoxide, methane, and carbon dioxide). A maximum H₂ yield (91.36% (0.064 mol^-1 g_cat⁻¹ h⁻¹)) was attained at the following conditions: 15 wt% Ni loading, steam to carbon molar ratio of 6.5, weight hourly space velocity of 1.05 h⁻¹, and 600 °C. The 15 wt% Ni catalyst maintained sufficient stability over 40 h reaction time. Accordingly, Ni-comp-ALC interactions were seen to efficiently improve the activity and stability of the catalyst so as to synergistically resist coke deposition and metal sintering through the formation of a large number of free Ni particles and oxygen vacancies.     

Activation behaviour of the Ni/MH batteries electrodic material Ni(OH)2 by single particle microelectrode technique

The activation process of Ni(OH)₂ used as the positive electrode active material of Ni/MH batteries was studied by a single particle microelectrode method thanks to an improved apparatus. The images of the Ni(OH)₂ particle during the charge process were collected. The electrochemical properties of Ni(OH)₂ were studied by cyclic voltammetry and galvanostatic charge/discharge of a single particle. The charge efficiency (η) of the single particle was as high as 94%. The normalized output rate (NOR) was proposed as a parameter to evaluate the output performance of the electrode material. The NOR value varied with the electrode potential value. But the NOR value remained constant at fixed electrode potential value during the activation process. This implies that the activation process did not improve the reaction rate of the particle, although the capacity kept increasing during the activation process. The intrinsic nature of the activation of Ni(OH)₂ was deduced as the formation of dispersed Ni(III) in the active mass. The Ni(III) phase was formed during the charge process and some remained unreduced during the discharge process. The remaining Ni(III) resulted in a much higher electronic conductivity of Ni(OH)₂.