Generation of hydrogen from sodium borohydride at low temperature using metal halides additive

A series of MnCl₂ impregnated NaBH₄ composite mixture was synthesized by facile solution method. The weight percent of MnCl₂ varied from 10 wt% to 50 wt% in sodium borohydride during synthesis of the material. The effects of other additives were also studied by considering CaCl₂, and ZnCl₂. The synthesized materials were characterized by using X-ray diffraction (XRD), TGA, FE-SEM, Raman spectroscopy, and Fourier Transform Infra-red spectroscopy (FTIR). The generation of hydrogen was monitored by using a Gas Chromatograph. The study suggested that the formation of a homogenous composite mixture and spherical structure of MnCl₂/NaBH₄ composite material. The optimum loading of additive was found to be 20 wt% MnCl₂ for the generation of hydrogen. The addition of additive assists in lowering the thermal decomposition temperature of sodium borohydride at 373 K. The order of thermolysis performance by addition of various additives was as follows: 20CaCl₂/NaBH₄ > 20MnCl₂/NaBH₄ > 20ZnCl₂/NaBH₄. However, the FTIR spectra and the thermolysis study suggested that the decomposition of NaBH₄ was incomplete at 373 K even by the addition of additives.     

Copper–iron mixed oxide catalyst precursors prepared by glycine-nitrate combustion method for ammonia borane dehydrogenation processes

The influence of the properties of copper ferrite, prepared by the combustion method from glycine-nitrate precursor, on the kinetics of NH₃BH₃ hydrolysis, thermolysis and hydrothermolysis are presented. As-prepared and annealed samples were studied by X-ray diffraction, scanning electron microscopy, differential dissolution, and attenuated total reflection infrared spectroscopy. It has been shown that in the hydrolysis and hydrothermolysis of NH₃BH₃, the as-prepared combustion product, which mainly consisted of a cubic spinel Cu_0.67Fe_2.33O₄ with Fe²⁺ higher content, had the highest activity, as compared with oxides of copper and iron and the annealed samples. According to transmission electron microscopy and X-ray diffraction, in the reaction medium copper ferrite is reduced to nanosized Cu⁰ and Fe⁰. This allowed the average rate of H₂ evolution per 1 g of the composition to be increased from 30 to 76 ml⋅min⁻¹, as compared with non-catalytic process. The high gravimetric hydrogen capacity (7.3 wt%) was observed at 90 °C.     

Ammonia borane thermolytic decomposition in the presence of metal (II) chlorides

In the present work, we studied the effect of metal chlorides, MCl₂, on the thermal decomposition of ammonia borane NH₃BH₃ (AB). Some metals from row n = 4 of the periodic table were chosen and used as MCl₂: namely, FeCl₂, CoCl₂, NiCl₂, CuCl₂, and ZnCl₂. In addition, three metals from column VIII of the periodic table were considered: NiCl₂, PdCl₂ and PtCl₂. The AB decomposition was followed by TGA and DSC; the decomposition gases analyzed by μGC/MSD coupling, and the solid by-products identified by XRD, IR and XPS. We observed that the presence of CuCl₂ in AB is beneficial, making the decomposition occur in much milder conditions than for pristine AB; for example, the dehydrogenation of CuCl₂-doped AB started at 25 °C, with the sample losing about 14 wt% at 85 °C. However, MCl₂ does not hinder the evolution of the undesired borazine; it only contributes to a decrease in its content compared to pristine AB. To rationalize the better performance of CuCl₂, we propose that Cu offers an optimal doping activity with intermediate binding energies for the intermediates: i.e. with H not too strongly bonded but optimally bonded to the N of AB. The germ Cu?NH₂–BH₂, then formed, acts as a Lewis acid through B and has an optimized reactivity towards a new AB molecule (head-to-tail dehydrocoupling). This is discussed herein.     

Reversible chemical hydrogen storage in borohydrides via thermolysis and hydrolysis: Recent advances,challenges, and perspectives

Efficient hydrogen storing alternatives are now been pursued for decades. Solid storage systems are currently highly researched due to high volumetric densities at low temperatures and pressure. Still, no developed systems have satisfied even close to the targets given by The United States Department of Energy (DOE) 2020. Although various systems have reported good outputs at nearly room temperatures. The boron-based hydrides (BBHs) are the typical materials. They show a maximum of four reacting B–H bonds and hence have high volumetric densities of hydrogen. The majority of the research has been dealing with dehydrogenation through thermolysis and hydrolysis. This article critically reviews different BBHs for effective hydrogen storage. The first materials reviewed are ammonia borane, lithium borohydride, and sodium borohydride. However, their progress declined in the past few years due to incomplete reactions, elevated dehydrogenation temperature, and purity of hydrogen produced. To overcome these issues, new materials using suitable dopants have been developed since 2000. These materials display enhanced operations along with few drawbacks. Regenerability and numerous other stability factors have been intensively analyzed in this review. Also, different strategies for a system to operate at room conditions have been critically discussed. The findings suggest that BBHs are potential candidates in the field of hydrogen storage, but their applicability highly depends upon the regenerability and recyclability of byproducts.     

Novel thermoelectric generator heat exchanger for indirect heat recovery from molten CuCl in the thermochemical Cu–Cl cycle of hydrogen production

The looming threat of global warming has elicited efforts to develop reliable sustainable energy resources. Hydrogen as a clean fuel is deemed a potential solution to the problem of storage of power from renewable energy technologies. Among current thermochemical hydrogen generation methods, the thermochemical copper-chlorine (Cu–Cl) cycle is of high interest owing to lower temperature requirements. Present study investigates a novel heat exchanger comprising a thermoelectric generator (TEG) to recover heat from high temperature molten CuCl exiting the thermolysis reactor. Employing casting/extrusion method, the performance of the proposed heat exchanger is numerically examined using COMSOL Multiphysics. Results indicate that maximum generated power could exceed 40 W at the matching current of 4.5 A. Maximum energy conversion efficiency yields to 7.1%. Results demonstrate that TEG performance boosts with increasing the inlet Re number, particularly at the hot end. For the molten CuCl chamber, findings denote that there is a 36% discrepancy between highest and lowest Re numbers. Similarly, the highest efficiency value pertains to the case with the highest inlet velocity. Moreover, the highest temperature difference between inlet and outlet of the cooling water is about 28 °C and 10 °C for the lowest and highest inlet Re numbers, respectively. Average deviation from anticipated friction factor and Nusselt number are 0.31% and 12.62%, respectively.     

An experimental study of neat and ionic liquid-aided ammonia borane thermolysis

This paper reports hydrogen (H₂) yield and reaction rate measurements of ammonia borane (AB) thermolysis in the neat form as well as facilitated by the presence of an ionic solvent, 1-butyl-3-methylimidazolium chloride (bmimCl). The measurements were conducted at various temperatures between 85 and 120 °C under quasi-isothermal conditions. The details of fast hydrogen evolution at the initial stage of the thermolysis process were captured for the first time. The presence of bmimCl led to significant increases in both the rate and the amount of hydrogen released, compared to the corresponding quantities at identical temperatures for neat AB thermolysis. Measurements reported in the literature are in qualitative agreement with this observation but lack the time resolution necessary for the quantitative comparisons. At 120 °C, the measured gravimetric H₂ storage capacity from the neat AB thermolysis was 9.9 wt% (material base) and that from the AB/bmimCl mixture (80/20 wt%) thermolysis was 11.2 wt%. Also, the reaction rate of the thermolysis of AB/bmimCl mixture (80/20 wt%) was twice as fast as that of the neat AB thermolysis at this temperature. In the bmimCl (20 wt%) aided AB thermolysis, a significant increase in the H₂ yield occurred at temperatures over 107 °C.     

洋葱状炭纳米粒子的无催化剂合成(英文)

描述了基于NaN3-C6Cl6混合物热解一步合成洋葱状碳纳米粒子的方法。应用EMS,XRD,Ramans研究了缓冲气体(Ar或空气)对炭产物的得率、形貌和结构的影响。产物包含洋葱炭、非晶碳和NaCl,通过简单的纯化处理即可完全除去副产物。洋葱状炭纳米粒子的形成由热解过程中压力迅速增加产生的震动波诱导苯基活性分子合并所制。     

Investigations into acrylamide precursors in sterilized table olives: Evidence of a peptic fraction being responsible for acrylamide formation

Formation of acrylamide from commercial model peptides containing protein-bound aspartic acid, alanine and methionine, respectively, at 200 °C and different times in the absence of any carbonyl sources, was demonstrated by HPLC–MS/MS analyses. Further experiments using a more complex model system based on olive water, i.e., the aqueous fraction of olive pulp from untreated and lye-treated green olives, were performed. After partial fractionation of olive water by solid-phase extraction, only peptides/proteins containing fractions, being devoid of free asparagine, generated significant amounts of acrylamide during less harsh heat treatment (121 °C for 30 min). In contrast, acrylamide was not detected after heating the same fraction under identical thermal conditions when previously subjected to acid hydrolysis. Consistently, significant amounts of acrylamide were released after heating the albuminous precipitate resulting from acetone precipitation of olive water. These results strongly support the role of peptides/proteins as precursors of acrylamide formation in sterilized olives.     

Gasification of biomass: comparison of fixed bed and fluidized bed gasifier

Gasification as a thermochemical process is defined and limited to combustion and pyrolysis. A systematic overview of reactor designs categorizes fixed bed and fluidized bed reactors. Criteria for a comparison of these reactors are worked out, i.e. technology, use of material, use of energy, environment and economy. A utility analysis for thermochemical processes is suggested. It shows that the advantages of one of the reactor types are marginal. An advantage mainly depends on the physical consistency of the input. As a result there is no significant advantage for the fixed bed or the fluidized bed reactor.     

Ammonia borane decomposition in the presence of cobalt halides

In the present work we studied the effect of cobalt halides (CoF₂, CoCl₂, CoBr₂ and CoI₂; also denoted CoX₂) on the thermal decomposition of ammonia borane NH₃BH₃ (AB) over the range 25-220 °C. The reaction was followed by thermogravimetric analysis and differential scanning calorimetry. The gaseous products analyzed by gas chromatography and mass spectrometry, and the solid by-products identified by elemental analysis: powder X-ray diffraction, infrared and X-ray photoelectron spectroscopies. Compared to pristine AB, the presence of CoCl₂ and CoBr₂ reduces both the induction period of the AB decomposition and the content of unwanted borazine in the H₂ stream, whereas the presence of CoI₂ or CoF₂ has little or no effect, respectively. We propose that the positive effect of CoX₂ comes from their electronic and steric effects, and that CoCl₂ is the compound which shows the best properties relative to these effects. Herein, the roles of Co and X are discussed and a revised mechanism of the AB dehydrocoupling initiation is proposed.