A new polyborate anion, [B7O9(OH)6]3−: Self assembly,XRD and thermal properties of s-fac-[Co(dien)2][B7O9(OH)6]·9H2O

The title compound, s-fac-[Co(dien)₂][B₇O₉(OH)₆]·9H₂O (1) (dien = HN(CH₂CH₂NH₂)₂), has been prepared as a crystalline solid in moderate yield (35%) from the reaction of B(OH)₃ with [Co(dien)₂][OH]₃ in aqueous solution (10:1 ratio). The structure contains a novel polyborate anion [B₇O₉(OH)₆]^3 − which is structurally based on the known ‘ribbon’ isomer of [B₇O₉(OH)₅]^2 −, with an additional [OH]⁻ group coordinated to a B atom in one of the outer boroxole rings. Compound 1 is formed by a self-assembly process in which the cation and anion mutually template themselves from equilibrium mixtures under reaction conditions. The [B₇O₉(OH)₆]^3 − anions are H-bonded to each other in layers with ‘cavities’ suitable for the [Co(dien]₂]^3 + complex. Three [B₇O₉(OH)₆]^3 − anions are in the secondary coordination sphere (via H-bonds) of each cation, with each anion H-bonded to three cations.     

A unique 3D Co(II)-MOF based on [Co6(μ3-OH)4]8 +n chains: Synthesis,crystal structure,and magnetic property

A novel metal-organic framework, [Co₆(μ₃-OH)₄(ndc)₄(bip)₂(H₂O)₂]_n (1)[H₂ ndc = 1,4-naphthalenedicarboxylic acid, bip = 1,5-bis(imidazole-1-yl)pentane], constructed from unique [Co₆(μ₃-OH)₄]^8 +_n chains containing alternate [Co₄(OH)₂]^6 + and [Co₂(OH)₂]^2 + subunits, was reported, which has a new (3,3,8,12)-connected or 12-connented fcu/cubic network and shows weak antiferromagnetic interaction between the adjacent Co(II) ions mediated through the carboxylate and hydroxyl groups.     

Basicity–FAME yield correlations in metal cation modified MgAl mixed oxides for biodiesel synthesis

In this paper Zn^2 +, Co^2 +, Fe^3 + and La^3 + were respectively introduced into Mg₃Al₁ mixed oxides to prepare Mg₁Zn₂Al₁, Mg₁Co₂Al₁, Mg₃Al_0.6Fe_0.4 and Mg₃Al_0.6La_0.4 oxides by calcinations at 773 K. The XRD, XPS, BET, ICP-AES and CO₂-TPD characterizations of samples exhibited that the effects of the substitution of trivalent cations (Fe^3 +, La^3 +) for Al^3 + on the basicity of samples were stronger than the substitution of divalent cations (Zn^2 +, Co^2 +) for Mg^2 + because of high O^2 − concentration which were coincident with the FAME yield for these catalysts. La^3 + modified catalyst exhibited highest activity in transesterification.     

Development of electrochemical cell with layered composite of the Gd-doped ceria/electronic conductor system for generation of H2–CO fuel through oxidation–reduction of CH4–CO2 mixed gases

This paper shows the recent results on the development of layered composite promoting two types of electrochemical reactions (oxidation and reduction) in one cell. This cell consisted of porous Ni–Gd-doped (GDC) ceria cathode/thin porous GDC electrolyte (50 μm)/porous SrRuO₃–GDC anode. The external electric current was flowed in this cell at the electric field strength of 1.25 and 6.25 V/cm. The mixed gases of CH₄ (30–70%) and CO₂ (70–30%) were fed at the rate of 50 ml/min to the cell heated at 400–800 °C under the electric field. In the cathode, CO₂ was reduced to CO (CO₂ + 2e^? → CO + O^2?) and the formed CO and O^2? ions were transported to the anode through the pores and surface and interior of grains of GDC film. On the other hand, CH₄ was oxidized in the anode to form CO and H₂ through the reaction with diffusing O^2? ions (CH₄ + O^2? → CO + 2H₂ + 2e^?). As a result, H₂–CO mixed fuel was produced from the CH₄–CO₂ mixed gases (CH₄ + CO₂ → 2H₂ + 2CO). This electrochemical reaction proceeded completely at 800 °C and no blockage of gases was measured for long time (>10 h). Only H₂–CO fuel was generated in the wide gas compositions of starting CH₄–CO₂ gases.     

Photocatalytic reduction of CO2 to energy products using Cu–TiO2/ZSM-5 and Co–TiO2/ZSM-5 under low energy irradiation

Copper or cobalt incorporated TiO₂ supported ZSM-5 catalysts were prepared by a sol–gel method, and then were characterized by XRD, BET, XPS and UV–vis diffuse reflectance spectroscopy. Ti^3 + was the main titanium specie in TiO₂/ZSM-5 and Cu–TiO₂/ZSM-5, which will be oxide to Ti^4 + after Co was doped. With the deposition of Cu or Co, the efficiency of the CO₂ conversion to CH₃OH was increased under low energy irradiation. The peak production rate of CH₃OH reached 50.05 and 35.12 μmol g^− 1 h^− 1, respectively. High photo energy efficiency (PEE) and quantum yield (φ) were also reached. The mechanism was discussed in our study.     

Honeycomb supported Co3O4/CeO2 catalyst for CO/CH4 emissions abatement: Effect of low Pd–Pt content on the catalytic activity

A structured Co₃O₄–CeO₂ composite oxide, containing 30% by weight of Co₃O_4, has been prepared over a cordieritic honeycomb support. The bimetallic, Pd–Pt catalyst has been obtained by impregnation of the supported Co₃O₄–CeO₂ with Pd and Pt precursors in order to obtain a total metal loading of 50 g/ft³.CO, CH₄ combined oxidation tests were performed over the catalyzed monoliths in realistic conditions, namely GHSV = 100,000 h⁻¹ and reaction feed close to emission from bi-fuel vehicles. The Pd–Pt un-promoted Co₃O₄–CeO₂ is promising for cold-start application, showing massive CO conversion below 100 °C, in lean condition.A strong enhancement of the CH₄ oxidation activity, between 400 and 600 °C, has been observed by addition to the Co₃O₄–CeO₂ of a low amount of Pd–Pt metals.     

Impact of metal doping on the activity of Au/CeO2 catalysts for catalytic abatement of VOCs and CO in waste gases

The catalytic performance in the total oxidation of CO and methanol over gold catalysts supported on ceria doped by different metal oxides (Me = Fe, Mn and Co) was studied and a strong influence of the nature of dopant was observed. The activity towards the oxidation of CO and CH₃OH was in the order: AuCeCo > AuCe > AuCeFe > AuCeMn. The characterization by XRD and HRTEM evidenced differences in the average size and the distribution of gold particles. AuCeCo catalyst exhibited superior low-temperature CO oxidation activity (100% conversion degree was obtained at 25 °C) and almost 100% total oxidation of CH₃OH at about 40 °C. Higher hydrogen consumption was estimated by means of TPR over this catalyst. The effect of modification with Co₃O₄ of Au/CeO₂ catalysts on their CO oxidation activity was further studied by varying of the dopant content (5, 10 and 15 wt.% Co₃O₄).     

New members in the [Mn10] supertetrahedron family

Two manganese complexes, [Mn^II₄Mn^III₆Cl₄(CH₃OCH₂CH₂O)₁₂ O₄][Mn^II₃Ti^IVCl₆(CH₃OCH₂CH₂O)₆] (1) and [Mn^II₄Mn^III₆Cl₄(CH₃OCH₂CH₂O)₁₂O₄] [Mn₄^II Cl₁₀(CH₃OCH₂CH₂OH)₄]∙0.5CH₃OCH₂CH₂OH, (2) have been obtained and characterized by single-crystal X-ray diffraction. Both structures consist of the decametallic dicationic [Mn^II₄Mn^III₆Cl₄(CH₃OCH₂CH₂O)₁₂O₄]^2 + core constructed by four vertex-sharing [Mn^III₃Mn^IIO]^9 + tetrahedra. Also, these compounds contain the different tetrametallic dianions: [Mn^II₃Ti^IVCl₆(CH₃OCH₂CH₂O)₆]^2 − (in complex 1) and [Mn₄^IICl₁₀(CH₃OCH₂CH₂OH)₄]^2 − (in complex 2). Magnetic dc and ac susceptibility measurements for compound (1) show that the dicationic decanuclear magnetic cluster possesses an S = 12 ± 1 spin ground-state.     

A facile ultrasonic process for the preparation of Co3O4 nanoflowers for room-temperature removal of low-concentration NOx

Co₃O₄ nanoflowers with high surface areas were synthesized with a facile template-free ultrasonic process and showed high performance on the removal of low-concentration (10 ppm) NO at room temperature. By doping Mg^2 + in the Co₃O₄ nanoflowers, improved performances of about 9 h for above 50% NO removal were obtained.     

Three cobalt (II) complexes with triethylenetetraaminehexaacetic acid: From binuclear complex to 3d-4f coordination polymers

The cobalt(II)–lanthanide(III) heteronuclear complexes [Ln(H₂O)₄Co₂(TTHA)(SCN)₂]·H₃O⁺ (H₆TTHA = triethylenetetraaminehexaacetic acid, Ln = La(2), Ce(3)) have been synthesized based on a binuclear building block of [Co₂(H₂TTHA)(H₂O)₂] in [Co₂(H₂TTHA)(H₂O)₂]·4H₂O (1). Single-crystal structures show that complex 1 is a binuclear complex, containing the [Co₂(H₂TTHA)(H₂O)₂] unit as a useful building block. Adding the La^3 + and Ce^3 + ions to this synthesis system, two new 3d-4f mixed complexes 2 and 3 were obtained. Complexes 2 and 3 show 3D framework, comprising an infinite 1D (one-dimensional) chain based on heterometallic Ln₂Co₂ (Ln = La(2), Ce(3)). Further investigations such as IR spectra, UV–vis spectra, TGA, XRD and magnetic properties were studied.     

Adsorption and temperature programmed desorption of NO,NO + O2, NO2 and NO + NO2 over CoH-ZSM-5

The NO₂, NO (O₂) adsorption and temperature programmed desorption (TPD) were studied systematically to probe into the selective catalytic reduction of NO by methane (CH₄–SCR) over CoH-ZSM-5 (SiO₂/Al₂O₃ = 25, Co/Al = 0.132–0.312). Adsorption conditions significantly affect the adsorption of NO, NO₂ and NO + O₂. Adsorbed NO species are unstable and desorbed below the reactive temperature 523 K. Increasing adsorption temperature results in the decrease of the adsorbed NO species amount. The amount of –NO_y species formed from NO₂ adsorption increases with the increase of NO₂ concentration in the adsorption process, while decreases significantly with the increase of adsorption temperature. Though NO species are adsorbed weakly on CoH-ZSM-5, competitive adsorption between NO and –NO_y species decreases the amount of adsorbed –NO_y species. Similar desorption profiles of NO₂ were obtained over CoH-ZSM-5 while they were contacted with NO₂ or NO + O₂ followed by TPD. If NO₂ was essential to form adsorbed –NO_y species, the amount of adsorbed –NO_y species for NO + O₂ adsorption should be the least among the adsorptions of NO₂, NO + O₂ and NO + NO₂ because of the lowest NO₂ concentration and highest NO concentration. In fact, the amount of adsorbed –NO_y species is between the other two adsorption processes. These indicate that the formation of adsorbed –NO_y species may not originate from NO₂.     

Synthesis,structure and electronic calculation of alkali metals borate Li2Na[B5O8(OH)2]

A new alkali metals borate complex, Li₂Na[B₅O₈(OH)₂], has been successfully synthesized by a facile hydrothermal method. Single-crystal X-ray diffraction analysis reveals that it crystallizes in orthorhombic space group Pbcn with a = 8.919(3) Å, b = 9.181(3) Å, c = 8.416(2) Å, Z = 4. The crystal structure is constructed of two dimensional (2D) [(B₅O₈)(OH)₂]_∞ layers, while stacking along b axis and then connected by Li⁺ and Na⁺ cations to extend to 3D framework Li₂Na[B₅O₈(OH)₂]. UV-vis-NIR spectrum shows that Li₂Na[B₅O₈(OH)₂] possesses a wide range of transparency and a UV cut-off edge below 190 nm which indicates that it may be applied in the deep ultraviolet region. The calculated band structures and the density of states indicate that Li₂Na[B₅O₈(OH)₂] is a direct band gap compound with a band gap of 5.68 eV. In addition, IR spectroscopy, thermal stability and theoretical calculations of Li₂Na[B₅O₈(OH)₂] are also reported in this work.     

Redox behavior and oxidation catalysis of HnXW12O40 (X = Co2 +, B3 +, Si4 +, and P5 +) Keggin heteropolyacid catalysts

Redox behavior and oxidation catalysis of H_nXW₁₂O₄₀ (X = Co^2 +, B^3 +, Si^4 +, and P^5 +) Keggin heteropolyacid catalysts were investigated. Successful formation of H_nXW₁₂O₄₀ catalysts was confirmed by diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy. Reduction potentials of H_nXW₁₂O₄₀ catalysts were determined by electrochemical measurements. First electron reduction potential of H_nXW₁₂O₄₀ catalysts decreased with increasing overall negative charge of heteropolyanion. H_nXW₁₂O₄₀ catalysts were then applied to the liquid-phase oxidation of benzaldehyde to benzoic acid. Yield for benzoic acid increased with increasing first electron reduction potential.     

Preparation and characterization of LiNi0.8Co0.15Al0.05O2 with high cycling stability by using AlO2- as Al source

We report the preparation of a series of LiNi_0.8Co_0.15Al_0.05O₂ materials with different reaction time (10, 20, 30 and 40 h) of precursor and their electrochemical properties as cathode material for lithium-ion batteries (LIBs). The preparation of LiNi_0.8Co_0.15Al_0.05O₂ was divided into two steps: a co-precipitation process to obtain Ni_0.8Co_0.15Al_0.05(OH)₂ precursor and a calcination step with LiOH. During the co-precipitation process, AlO₂^- was employed as Al source so as to guarantee Ni²⁺, Co²⁺ and Al³⁺ co-precipitation. The impacts of different synthesis time of the precursor on crystal structure, morphology and electrochemical performance of LiNi_0.8Co_0.15Al_0.05O₂ were systematically investigated. The samples with various synthesis time of precursor possessed spherical morphology and a layered α-NaFeO₂ structure with R-3m space group. Especially, when the reaction time of precursor was 30 h, the LiNi_0.8Co_0.15Al_0.05O₂ had the weakest degree of Li⁺/Ni²⁺ ions mixing and the best uniformity and integrity. When used as cathode materials for LIBs, the LiNi_0.8Co_0.15Al_0.05O₂ with 30 h exhibited high discharge capacity, good cycling performance and remarkable rate capability. The maximum discharge capacity was 202.3 mAh g⁻¹ at 0.1 C and the capacity retention approached 99.4% after 100 cycles at 1 C. At 10 C, the discharge capacity exceeded 140 mAh g⁻¹, suggesting a possible application in the high rate LIBs. The excellent electrochemical performance might be attributed to the uniform co-precipitation of Ni²⁺, Co²⁺ and Al³⁺ and well layered structure with less Li⁺/Ni²⁺ mixing.     

Quantitative characterization of the solid acidity of montmorillonite using combined FTIR and TPD based on the NH3 adsorption system

The complete parameters of montmorillonite solid acidity, namely amount, strength, and types of acidity, were determined and the properties of the acid sites after heating were proposed by combining the temperature-programmed desorption (TPD) and Fourier transform infrared spectroscopy (FTIR) based on the NH₃ adsorption system. The total amount of montmorillonite acid sites was 1.15 mmol/g, which was higher than the value obtained by the Hammett indicator method because of the detection of solid acid sites in the montmorillonite interlayer space. These acid sites were composed of 1.00 mmol/g Brønsted and 0.15 mmol/g Lewis acid sites. The acidity of montmorillonite was primarily derived from the interlayer polarized water, Si–OH, H₃O⁺ adsorbed by negatively charged tetrahedral AlO₄, and unsaturated Al^3 + ions, all of which were attributed to the Brønsted acid sites with the exception of the unsaturated Al^3 + ions (Lewis acid sites). Heating led to an increase in the acid strength and the acid amount and altered the type of the partial acid sites. The interlayer polarized water provided more protons after heating at 120 °C and exhibited higher acid strength than that of raw montmorillonite. After heating at 400 °C, the interlayer polarized water acted as very strong acid sites. The H₃O⁺ adsorbed by tetrahedral AlO₄ was attributed to weak-strength acid sites and transformed into Si–O(H)–Al after dehydration, while displaying strong-strength acidity. The unsaturated Al^3 + ions showed medium-strength Lewis acidity, although a portion of these ions adsorbed water molecules and exhibited weak Brønsted acidity. After dehydroxylation at 600 °C, an abundance of unsaturated Al^3 + ions appeared and the amount of Lewis acid sites increased.     

High-pressure adsorption of methane on montmorillonite,kaolinite and illite

Methane (CH₄) adsorption of Ca^2 +-montmorillonite (Mt), kaolinite (Kaol) and illite (Il) at 60 °C and pressures up to 18.0 MPa was investigated, during which the adsorption capacity was evaluated by the Langmuir adsorption model. The influences of adsorbed water and the interlayer distance of the clay minerals on CH₄ adsorption were explored by using heated Mt products with different interlayer distances as the adsorbent. Mt, Kaol and Il showed high CH₄ adsorption capacities, and their maximum Langmuir adsorption capacities were Mt, 6.01 cm³/g; Kaol, 3.88 cm³/g; and Il, 2.22 cm³/g, respectively. CH₄ was adsorbed only on the external surface of Kaol and Il; however, adsorption also occurred in the interlayer space of Mt, which had a larger interlayer distance than the size of a CH₄ molecule (0.38 nm). CH₄ adsorption in the interlayer space of Mt was supported by the lower CH₄ adsorption capacity of heated Mt products (with the interlayer distance < 0.38 nm) than that of Mt at high pressures despite the higher external surface areas of the heated Mt samples. The entrance of CH₄ into the interlayer space of Mt occurred at low pressures, and more CH₄ molecules entered the interlayer space at high pressures. Moreover, the adsorbed water occupied the adsorption sites of the clay minerals and decreased the CH₄ adsorption capacity. These results indicate that clay minerals play a significant role in CH₄ adsorption of shale and indicate that the structure and surface properties of clay minerals are the important parameters for estimating the gas storage capacity of shale.     

Facile synthesis of three dimensional flower-like Co3O4@MnO2 core-shell microspheres as high-performance electrode materials for supercapacitors

In this work, we reported the synthesis of three dimensional flower-like Co₃O₄@MnO₂ core-shell microspheres by a controllable two-step reaction. Flower-like Co₃O₄ microspheres cores were firstly built from the self-assembly of Co₃O₄ nanosheets, on which MnO₂ nanosheets shells were subsequently grown through the hydrothermal decomposition of KMnO₄. The MnO₂ nanosheets shells were found to increase the electrochemical active sites and allow faster redox reaction kinetics. Based on these advantages, when used as an electrode for supercapacitors, the prepared flower-like Co₃O₄@MnO₂ core-shell composite electrode demonstrated a significantly enhanced specific capacitance (671 F g⁻¹ at 1 A g⁻¹) as well as improved rate capability (84% retention at 10 A g⁻¹) compared with the pristine flower-like Co₃O₄ electrode. Moreover, the optimized asymmetric supercapacitor device based on the flower-like Co₃O₄@MnO₂//active carbon exhibited a high energy density of 34.1 W h kg⁻¹ at a power density of 750 W kg⁻¹, meaning its great potential application for energy storage devices.     

Promising high temperature thermoelectric properties of dense Ba2Co9O14 ceramics

Layered cobalt oxides have shown high thermoelectric properties. The n = 1 member of the Ba_n+1Co_nO_3n+3(Co₈O₈) family, Ba₂Co₉O₁₄, a new layered cobalt oxides family with Co(II) and Co(III) in the CdI₂ layers, has been synthesized by solid state reaction and sintered as dense ceramics (relative density ∼ 93%) by Spark Plasma Sintering. It presents promising p-type thermoelectric properties at high temperature. The dimensionless figure of merit ZT is 0.032 at 660 K and 0.04 at 1000 K, which is about one quarter to one third of the ZT value of Ca₃Co₄O₉ ceramics.     

Anelastic spectroscopy for studying O vacancies in perovskites

We present the results of anelastic relaxation experiments (2–30 kHz) on ceramic SrTiO₃ subjected to reduction in H₂ atmosphere, which yield a balance between V_O and (OH)⁻ defects. The resulting anelastic spectrum contains, besides the well-known structural transformation near 110 K, several thermally activated relaxation processes between 200 and 700 K. The two main elastic energy loss peaks are proposed to provide the first measurement of the hopping rate of V_O –(OH)⁻ defects in pure SrTiO₃.     

Hierarchical Co3O4@ZnWO4 core/shell nanostructures on nickel foam: Synthesis and electrochemical performance for supercapacitors

To improve the electrochemical properties of Co₃O₄ for supercapacitors application, a hierarchical Co₃O₄@ZnWO₄ core/shell nanowire arrays (NWAs) material is designed and synthesized successfully via a facile two-step hydrothermal method followed by the heat treatment. Co₃O₄@ZnWO₄ NWAs exhibits excellent electrochemical performances with areal capacitance of 4.1 F cm⁻² (1020.1 F g⁻¹) at a current density of 2 mA cm⁻² and extremely good cycling stability (99.7% of the initial capacitance remained even after 3000 cycles). Compared with pure Co₃O₄ electrodes, the results prove that this unique hierarchical hybrid nanostructure and reasonable assembling of two electrochemical pseudocapacitor materials are more advantageous to enhance the electrochemical performance. Considering these remarkable capacitive behaviors, the hierarchical Co₃O₄@ZnWO₄ core/shell NWAs nanostructure electrode can be revealed promising for high-performance supercapacitors.