- Sound Velocities, Elasticity, and Mechanical Properties of Stoichiometric Submicron Polycrystalline δ-MoN at High Pressure
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Acoustic velocities and elasticity of stoichiometric submicron polycrystalline δ-MoN have been reported at high pressure using ultrasonic measurements and first-principles calculations. Using the finite-strain equation-of-state approach, the bulk modulus
- Zou, Yongtao,Liu, Ke,Wang, Pei,Wang, Daowei,Li, Mu,Li, Ying,Fang, Leiming,Zhuo, Hongbin,Ruan, Shuangchen,Zhou, Cangtao,Zhao, Yusheng
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- CRYSTAL CHEMISTRY OF THE NEW RARE-EARTH SODIUM BORATES Na3Ln(BO3)2(Ln equals La, Nd).
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The ternary borate systems Na//2O-Ln//2O//3-B//2O//3 (Ln equals La, Nd) have been investigated in view of obtaining high-neodymium-concentration materials with weak concentration quenching. A ternary phase of composition Na//3Ln (BO//3)//2 (Ln equals La, Nd) has been found. It crystallzes in the monoclinic space group P2//1/c. The structure has been determined for Na//3Nd(BO//3)//2. A full-matrix least-square refinement led to R equals 0. 040. The structure is formed by isolated BO//3 triangles held together by the neodymium and sodium ions. The rare-earth atoms have a complex eightfold coordination in a covalent BO//3 matrix.
- Mascetti,Vlasse,Fouassier
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- Study of vaporization of sodium metaborate by transpiration thermogravimetry and knudsen effusion mass spectrometry
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The vaporization of solid sodium metaborate NaBO2(s) was studied by transpiration thermogravimetry (TTG) and Knudsen effusion mass spectrometry (KEMS). The transpiration measurements, performed for the first time on NaBO2(s), involved use of argon as the carrier gas for vapor transport and derivation of vapor pressure of NaBO2(g) (by assuming it as the sole vapor species) through many flow-dependence runs and temperature-dependence runs in the temperature range 1075-1218 K. The KEMS measurements performed in the temperature range 1060-1185 K confirmed NaBO 2(g) as the principal vapor species over NaBO2(s), in accord with the previously reported KEMS studies. The values of p(NaBO 2) obtained by both TTG and KEMS are consistent within the uncertainties associated with each method and so are the second-and third-law values of enthalpy of sublimation, the latter aspect consistently missing in all previous vaporization studies. The results of both TTG and KEMS were combined to recommend the following thermodynamic parameters pertinent to the sublimation reaction, NaBO2(s) = NaBO2(g): Log{p(NaBO 2)/Pa} = -(17056 ?± 441)/(T/K) + (14.73 ?± 0.35) for the temperature range 1060-1218 K; ??rHo m(298.15 K) = (346.3 ?± 9.4) kJa?￠mol-1; and ??rSom(298.15 K) = (210.2 ?± 6.8) Ja?￠mol-1a?￠K-1. ? 2011 American Chemical Society.
- Lakshmi Narasimhan,Viswanathan,Nalini
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- Investigation of the reaction mechanism and kinetics of production of anhydrous sodium metaborate (NaBO2) by a solid-state reaction
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In this study, the solid-state reaction mechanism and kinetics were investigated for production of anhydrous sodium metaborate (NaBO2), an industrially and technologically important boron compound. To assess the kinetics of solid-state production of NaBO2, the chemical reaction between borax (Na2B4O7) and sodium hydroxide (NaOH) was investigated by use of the thermal analysis techniques thermogravimetry (TG) and differential thermal analysis (DTA). DTA curves obtained under non-isothermal conditions at different heating rates (5, 10 and 20 C/min), revealed five endothermic peaks corresponding to five solid-state reactions occurring at 70, 130, 295, 463, and 595 C. The stages of the solid-state reaction used for production NaBO2 were also analyzed by XRD, which showed that at 70 and 130 C, Na2B4O7 and NaOH particles contacted between the grains, and diffusion was initiated at the interface. However, there was not yet any observable formation of NaBO 2. Formation of NaBO2 was initiated and sustained from 295 to 463 C, and then completed at 595 C; the product was anhydrous NaBO 2. Activation energies (E a) of the solid-state reactions were calculated from the weight loss based on the Arrhenius model; it was found that in the initial stages of the solid-state reaction E a values were lower than in the last three steps.
- Pi?kin, Mehmet Bur?in,Figen, Aysel Kantürk,Ergüven, Hatice
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- Hierarchical porous ZIF-8 for hydrogen production: Via the hydrolysis of sodium borohydride
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Hydrides show good performance for hydrogen gas storage/release. However, hydrogen gas release from hydrides via hydrolysis is a slow process and thus requires a catalyst. Herein, terephthalic acid (TPA) is used for the synthesis of a hierarchical porous zeolitic imidazolate framework (HPZIF-8). A mechanistic study of materials synthesis involved an in situ synthesis of zinc hydroxide nitrate nanosheets with an interplanar distance of 0.97 nm. Terephthalic acid modulates the pH value of the synthesis solution leading to the formation of HPZIF-8 with the Brunauer-Emmett-Teller (BET) surface area, Langmuir surface area, and total pore size of 1442 m2 g-1, 1900 m2 g-1, and 0.69 cm3 g-1, respectively. The formed phases during the synthesis undergo fast conversion to HPZIFs at room temperature. The application of the prepared materials in the hydrolysis of NaBH4 is reported. Acidity plays an important role in the catalytic performance of the materials. ZIF-8 prepared using terephthalic acid shows high catalytic activity with a hydrogen rate of 2333 mLH2 min-1 gcat-1 (8046 mLH2 min-1 gZn-1). The material exhibits high catalytic activity without any deterioration of its performance for several uses during continuous NaBH4 feeding. There are no changes in the material's structure after catalysis indicating the high recyclability of the materials.
- Abdelhamid, Hani Nasser
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p. 4416 - 4424
(2020/04/20)
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- Closing the Loop for Hydrogen Storage: Facile Regeneration of NaBH4 from its Hydrolytic Product
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Sodium borohydride (NaBH4) is among the most studied hydrogen storage materials because it is able to deliver high-purity H2 at room temperature with controllable kinetics via hydrolysis; however, its regeneration from the hydrolytic product has been challenging. Now, a facile method is reported to regenerate NaBH4 with high yield and low costs. The hydrolytic product NaBO2 in aqueous solution reacts with CO2, forming Na2B4O7?10 H2O and Na2CO3, both of which are ball-milled with Mg under ambient conditions to form NaBH4 in high yield (close to 80 %). Compared with previous studies, this approach avoids expensive reducing agents such as MgH2, bypasses the energy-intensive dehydration procedure to remove water from Na2B4O7?10 H2O, and does not require high-pressure H2 gas, therefore leading to much reduced costs. This method is expected to effectively close the loop of NaBH4 regeneration and hydrolysis, enabling a wide deployment of NaBH4 for hydrogen storage.
- Huang, Zhenguo,Liu, Jiangwen,Ouyang, Liuzhang,Shao, Huaiyu,Wang, Hui,Zhong, Hao,Zhu, Min,Zhu, Yongyang
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supporting information
p. 8623 - 8629
(2020/03/30)
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- UiO-66 as a catalyst for hydrogen production: Via the hydrolysis of sodium borohydride
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The exploration of a highly efficient catalyst for the hydrolysis of sodium borohydride (NaBH4) is a valuable step toward a hydrogen economy. UiO-66 (Universitetet i Oslo) was synthesized via a solvothermal method using acetic acid as a modulator. The material was characterized using X-ray diffraction (XRD), nitrogen adsorption-desorption isotherms, Fourier transform infrared (FT-IR) spectroscopy, thermogravimetric analysis (TGA), temperature-programmed desorption (TPD), and transmission electron microscopy (TEM). Data analysis reveals the formation of a pure and highly crystalline phase of UiO-66 with the Brunauer-Emmett-Teller (BET) and Langmuir specific surface areas of 1125 m2 g-1, and 1250 m2 g-1, respectively. UiO-66 was analysed as a catalyst for hydrogen generation via the hydrolysis of NaBH4. The effect of the NaBH4 amount and catalyst loading was investigated. The reaction time decreased with an increase of the amount of NaBH4 or UiO-66. UiO-66 exhibited an average hydrogen generation rate of 6200 mL min-1 g-1. The high catalytic performance of UiO-66 could be due to its large surface area and acidic sites. The results suggested that UiO-66 showed high potential to catalyze the hydrogen production via the hydrolysis of hydrides. This journal is
- Abdelhamid, Hani Nasser
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p. 10851 - 10857
(2020/09/02)
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- Ultrasound-assisted synthesis of alkali metals diselenides (M2Se2) and their application for the gram-scale preparation of 2,2’-diselenobis(benzoic acid)
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A simple and efficient method to convert elemental selenium into alkali metal diselenide was developed. The use of selenium and metal borohydride in a molar ratio of 1 to 0.125 in the presence of base, under “on water” conditions and ultrasound activation permitted the reduction of Se into Se22- to be completed within minutes. Thus obtained metal diselenide aqueous solution was then used in the multigram scale synthesis of 2,2’-diselenobis(benzoic acid) (DSBA) a valuable building block for the development of diverse and pivotal selenorganic compounds.
- Krasowska, Dorota,Begini, Francesca,Santi, Claudio,Mangiavacchi, Francesca,Drabowicz, Jozef,Sancineto, Luca
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- Thermoanalytical and NMR investigation of NaBH4·2H2O thermolysis process
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The article describes the thermolysis process of sodium borohydride dihydrate in thermoanalytical experiments. The reaction was carried out without solid catalyst and with catalyst as cobalt boride Co2B. It has been found out that in both cases the process starts after the peritectic reaction of the starting compound and forms a liquid phase. The enthalpy of peritectic reaction is ΔHreact?=?19?±?2?kJ?mol?1. When thermolysis proceeds in acetonitrile solution without a catalyst intermediate hydroxyborohydride NaBH3OH and/or Na(BH3)2OH is formed according to the NMR experiment data. The formation of similar complexes in the solid phase is confirmed by experiments on the oxidation of the thermolysis products. Thermolysis process with solid catalyst proceeds with an intense exothermic effect at lower temperatures. The kinetics of the non-catalytic process is described by the model of two consecutive reactions, and reaction with the solid catalyst model is approximated by two parallel reactions.
- Arkhangelskii,Tarasov,Kravchenko,Kirakosyan,Tsvetkov,Solovev,Dobrovolskii, Yu. A.,Shihovzev
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p. 2833 - 2842
(2017/11/23)
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- Influence of preparation conditions of hollow silica-nickel composite spheres on their catalytic activity for hydrolytic dehydrogenation of ammonia borane
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In this paper, we investigated influence of preparation conditions of hollow silica-nickel composite spheres on their morphology and catalytic activity for hydrolytic dehydrogenation of ammonia borane. In the preparation method of this study, when silica-nickel composite shells were coated on polystyrene templates by the sol-gel method using L(+)-arginine as the promoter for the reaction to form silica-nickel composite shell, the polystyrene templates were dissolved subsequently, even synchronously, in the same medium to form hollow spheres. The as-prepared silica-nickel composite spheres were characterized by transmission electron microscopy and scanning electron microscopy. The effects of Si+Ni content on the morphology were systematically evaluated. All the as-prepared hollow silica-nickel composite spheres have the similar morphology as identified by SEM and TEM measurement. Homogeneity of the hollow silica-nickel composite spheres increases with the increase in the Si+Ni content as shown by the laser diffraction particle size analysis. The catalytic activities of the hollow silica-nickel composite spheres for hydrolytic dehydrogenation of ammonia borane prepared with different Si+Ni contents were compared. The catalytic activity for the hydrogen evolution in the presence of the hollow spheres increases with the increase of Si+Ni content. The results of FTIR spectra of the hollow silica-nickel composite spheres indicate that a certain amount of residual PS templates exists in hollow silica-nickel composite spheres. The residual PS templates was able to be reduced by procedure of as-prepared samples with toluene solvent. The catalytic activity of hollow silica-nickel composite spheres increases with decrease in the amount of residual PS templates.
- Umegaki, Tetsuo,Seki, Ayano,Xu, Qiang,Kojima, Yoshiyuki
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p. 615 - 621
(2014/01/06)
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- Water dispersible acetate stabilized ruthenium(0) nanoclusters as catalyst for hydrogen generation from the hydrolysis of sodium borohyride
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The development of new storage materials will facilitate the use of hydrogen as a major energy vector in near future. In the hydrogen economy, chemical hydrides such as NaBH4, KBH4, LiH, NaH have been tested as precursor materials for supplying hydrogen at ambient temperature. Among these chemical hydrides, sodium borohydride (NaBH4) provides a safe and practical mean of producing hydrogen. Sodium borohydride is stable in basic solution; however, hydrolysis generates hydrogen gas in the presence of a suitable catalyst. All of the prior catalysts having been used for this hydrolysis reaction are heterogeneous and, therefore, have limited activity because of the surface area. Here, we report the employment of water dispersible metal(0) nanoclusters as catalyst for the hydrolysis of sodium borohydride. The water dispersible ruthenium(0) nanoclusters were prepared from the reduction of RuCl3·3H2O and stabilized by using acetate ion. They provide 5170 turnovers in the hydrolysis of sodium borohydride at 25.0 ± 0.1 °C before deactivation. The acetate stabilized ruthenium(0) nanoclusters of 2.8 ± 1.4 nm particle size were characterized by TEM, XPS, and FTIR spectroscopy. Kinetic study shows that the ruthenium(0) nanocluster-catalyzed hydrolysis of sodium borohydride is first order in catalyst concentration and zero order in substrate concentration. The acetate stabilized ruthenium(0) nanoclusters provide a low activation energy for the hydrolysis of sodium borohydride. Even in basic solution, the activation energy was found to be smaller than that obtained by using the carbon-supported ruthenium as catalyst.
- Zahmakiran, Mehmet,?zkar, Saim
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- Study on degradation of filamentary Ni catalyst on hydrolysis of sodium borohydride
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An investigation of durability characteristics of a pasted filamentary Ni catalyst was performed and extensive approaches for elucidating the degradation mechanism of the catalyst were undertaken. The H2 generation rate of pasted filamentary Ni catalyst gradually decreases with cycling and 76% of the initial H2 generation rate remains at 200cycles. After 200cycles, SEM images show an agglomeration of catalyst particles and a film on the pasted catalyst. An agglomeration of catalyst results in a reduction of specific surface area, as indicated by BET analysis, and a film on the pasted catalyst was formed by an accumulation of potassium originating from alkaline solution, and sodium and boron, which consists of Na2B4O 7·10H2O, a potassium borate compound (KB xOy) and boron oxide (B2O3), as indicated by XRD and XPS analyses. Consequently, a deterioration of the catalyst upon hydrolysis of sodium borohydride results from agglomeration of the catalyst and the film formed on the catalyst.
- Kim, Jin-Ho,Kim, Ki-Tae,Kang, Yong-Mook,Kim, Hyun-Seok,Song, Min-Sang,Lee, Yong-Ju,Lee, Paul S.,Lee, Jai-Young
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p. 222 - 227
(2008/10/09)
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