Fabrication of Activated Carbon Derived from Glycerin Pitch for Desulfurization of Model Fuel Oil and Electrode Application.

One of the world's challenging energy issues is introducing practical and affordable technology for organosulfur removal in fuel. Adsorptive desulfurization (ADS) can address this issue if highly effective activated carbon (AC) derived from industrial waste with excellent textural properties is used. In this study, the derived ACs from glycerin pitch loaded with P and Fe (AC/P and AC/Fe) were used as adsorbents for the ADS of model fuel oils, such as dibenzothiophene (DBT) at mild operating conditions. Under the optimized experimental conditions, 0.3 g of adsorbent dosage, 60 min reaction time, 30 °C temperature, and pH 4, the maximal DBT removal of 96.28 and 43.64%, respectively, for AC/P and AC/Fe was realized. The results indicated that the phosphorus-doped AC/P increases the selectivity of the ADS mechanism for DBT removal. Kinetic investigations disclosed that the adsorption process follows second-pseudo-order kinetics and the Langmuir adsorption isotherm model. The adsorbents remained active for five successive reuses, indicating their robust real-world applications. The electrochemical properties of the fabricated carbon electrodes were analyzed via cyclic voltammetry by coating the ACs with polytetrafluoroethylene (PTFE) as a binder. The transition-metal-doped AC/Fe, though exhibiting 5 times lower surface area, showed the highest specific capacitance at a scan rate of 5 mVs-1 (0.65 µF cm-2). Similarly, the extended AC:PTFE capacitor at a 10% binder ratio offered the maximum capacitance value (1.13 µF cm-2). The synthesized ACs demonstrated potential application as an electrode material, and hence glycerin pitch could be a low-cost precursor to improve the feasibility of commercial production of AC.

Realizing room temperature catalytic hydrogenation of sodium phenoxide by Ru/TiO2 for hydrogen storage.

Sodium phenoxide is a potentially promising hydrogen storage material due to its high hydrogen capacity and enhanced thermodynamic properties. Nevertheless, efficient catalysts are still lacking due to the high kinetic barrier for the reversible hydrogen uptake and release of sodium phenoxide. In the current work, a comparative study on the catalytic hydrogenation of sodium phenoxide was conducted. To our delight, a simple yet effective ruthenium-based catalyst was identified to respond aggressively to hydrogen in the solid-state hydrogenation of sodium phenoxide even at room temperature. The activity was enhanced by 6 fold with the as-synthesized 5.0% Ru/TiO2 catalyst as compared to that with commercial 5.0% Ru/Al2O3, respectively, under the same conditions.

Nanosizing Approach-A Case Study on the Thermal Decomposition of Hydrazine Borane.

Hydrazine borane (HB) is a chemical hydrogen storage material with high gravimetric hydrogen density of 15.4 wt%, containing both protic and hydridic hydrogen. However, its limitation is the formation of unfavorable gaseous by-products, such as hydrazine (N2H4) and ammonia (NH3), which are poisons to fuel cell catalyst, upon pyrolysis. Previous studies proved that confinement of ammonia borane (AB) greatly improved the dehydrogenation kinetics and thermodynamics. They function by reducing the particle size of AB and establishing bonds between silica functional groups and AB molecules. In current study, we employed the same strategy using MCM-41 and silica aerogel to investigate the effect of nanosizing towards the hydrogen storage properties of HB. Different loading of HB to the porous supports were investigated and optimized. The optimized loading of HB in MCM-41 and silica aerogel was 1:1 and 0.25:1, respectively. Both confined samples demonstrated great suppression of melting induced sample foaming. However, by-products formation was enhanced over dehydrogenation in an open system decomposition owing to the presence of extensive Si-O···BH3(HB) coordination that further promote the B-N bond cleavage to release N2H4. The Si-OH···N(N2H4) hydrogen bonding may further promote N-N bond cleavage in the resulting N2H4, facilitating the formation of NH3. As temperature increases, the remaining N-N-B oligomeric chains in the porous silica, which are lacking the long-range structure may further undergo intramolecular B-N or N-N cleavage to release substantial amount of N2H4 or NH3. Besides open system decomposition, we also reported a closed system decomposition where complete utilization of the N-H from the released N2H4 and NH3 in the secondary reaction can be achieved, releasing mainly hydrogen upon being heated up to high temperatures. Nanosizing of HB particles via PMMA encapsulation was also attempted. Despite the ester functional group that may favor multiple coordination with HB molecules, these interactions did not impart significant change towards the decomposition of HB selectively towards dehydrogenation.

Recent Advances in Anodes for Microbial Fuel Cells: An Overview.

The recycling and treatment of wastewater using microbial fuel cells (MFCs) has been attracting significant attention as a way to control energy crises and water pollution simultaneously. Despite all efforts, MFCs are unable to produce high energy or efficiently treat pollutants due to several issues, one being the anode's material. The anode is one of the most important parts of an MFC. Recently, different types of anode materials have been developed to improve the removal rate of pollutants and the efficiency of energy production. In MFCs, carbon-based materials have been employed as the most commonly preferred anode material. An extensive range of potentials are presently available for use in the fabrication of anode materials and can considerably minimize the current challenges, such as the need for high quality materials and their costs. The fabrication of an anode using biomass waste is an ideal approach to address the present issues and increase the working efficiency of MFCs. Furthermore, the current challenges and future perspectives of anode materials are briefly discussed.

Sodium anilinide-cyclohexylamide pair: synthesis, characterization, and hydrogen storage properties.

The lack of efficient hydrogen storage material is one of the bottlenecks for the large-scale implementation of hydrogen energy. Here, a series of new hydrogen storage materials, i.e., anilinide-cyclohexylamide pairs, are proposed via the metallation of an aniline-cyclohexylamine pair. DFT calculations show that the enthalpy change of hydrogen desorption (ΔHd) can be significantly tuned from 60.0 kJ per mol-H2 for the pristine aniline-cyclohexylamine pair to 42.2 kJ per mol-H2 for sodium anilinide-cyclohexylamide and 38.7 kJ per mol-H2 for potassium anilinide-cyclohexylamide, where an interesting correlation between the electronegativity of the metal and the ΔHd was observed. Experimentally, the sodium anilinide-cyclohexylamide pair was successfully synthesised with a theoretical hydrogen capacity of 4.9 wt%, and the hydrogenation and dehydrogenation cycle can be achieved at a relatively low temperature of 150 °C in the presence of commercial catalysts, in clear contrast to the pristine aniline-cyclohexylamine pair which undergoes dehydrogenation at elevated temperatures.

Metallo-N-Heterocycles - A new family of hydrogen storage material.

Storing hydrogen efficiently in condensed materials is a key technical challenge. Tremendous efforts have been given to inorganic hydrides containing B-H, Al-H and/or N-H bonds, while organic compounds with a great variety and rich chemistry in manipulating C-H and unsaturated bonds, however, are undervalued mainly because of their unfavourable thermodynamics and selectivity in dehydrogenation. Here, we developed a new family of hydrogen storage material spanning across the domain of inorganic and organic hydrogenous compounds, namely metallo-N-heterocycles, utilizing the electron donating nature of alkali or alkaline earth metals to tune the electron densities of N-heterocyclic molecules to be suitable for hydrogen storage in terms of thermodynamic properties. Theoretical calculations reveal that the enthalpies of dehydrogenation (ΔHd) of these metallo-N-heterocycles are dependent on the electronegativity of the metals. In line with our calculation results, sodium and lithium analogues of pyrrolides, imidazolides and carbazolides of distinct structures were synthesized and characterized for the first time, where the cation-π interaction was identified. More importantly, a reversible hydrogen absorption and desorption can be achieved over lithium carbazolide which has a hydrogen capacity as high as 6.5 wt% and a suitable enthalpy of dehydrogenation of 34.2 kJ mol-1-H2 for on-board hydrogen storage.

Synthesis, structure and the dehydrogenation mechanism of calcium amidoborane hydrazinates.

The calcium amidoborane hydrazinates, Ca(NH2BH3)2·nN2H4, were firstly synthesized by reacting different molar ratios of Ca(NH2BH3)2 and N2H4. In particular, Ca(NH2BH3)2 and N2H4 with a molar ratio of 1 : 2 crystallizes into the orthorhombic symmetry P212121 space group with the lattice parameters of a = 6.6239(4) Å, b = 13.7932(6) Å, c = 4.7909(2) Å. The dehydrogenations of calcium amidoborane hydrazinates are two-step reactions, exhibiting superior dehydrogenation properties compared with those of pristine Ca(NH2BH3)2. For Ca(NH2BH3)2-1/2N2H4, approximately 4.6 equiv. hydrogen (or 7.9 wt% hydrogen) can be released at 150 °C. Kinetic analysis shows that the activation energies for the two steps of hydrogen desorption from Ca(NH2BH3)2·2N2H4 are much lower than those of pristine Ca(NH2BH3)2, suggesting an improvement in the dehydrogenation kinetics of Ca(NH2BH3)2 after coordinating with N2H4. Isotopic labeling results show that the driving force for the dehydrogenation of calcium amidoborane hydrazinates is the combination mechanism of protonic hydrogen and hydridic hydrogen (H(δ+) and H(δ-)). In addition, initial H2 release from calcium amidoborane hydrazinates originates from the interaction of [-BH3] and N2H4, rather than [-BH3] and [-NH2] (in [-NH2BH3]).

Synthesis, thermal behavior, and dehydrogenation kinetics study of lithiated ethylenediamine.

The lithiation of ethylenediamine by LiH is a stepwise process to form the partially lithiated intermediates LiN(H)CH2 CH2 NH2 and [LiN(H)CH2 CH2 NH2 ][LiN(H)CH2 CH2 N(H)Li]2 prior to the formation of dilithiated ethylenediamine LiN(H)CH2 CH2 N(H)Li. A reversible phase transformation between the partial and dilithiated species was observed. One dimensional {Lin Nn } ladders and three-dimensional network structures were found in the crystal structures of LiN(H)CH2 CH2 NH2 and LiN(H)CH2 CH2 N(H)Li, respectively. LiN(H)CH2 CH2 N(H)Li undergoes dehydrogenation with an activation energy of 181±8 kJ mol(-1) , whereas the partially lithiated ethylenediamine compounds were polymerized and released ammonia at elevated temperatures. The dynamical dehydrogenation mechanism of the dilithiated ethylenediamine compounds was investigated by using the Johnson-Mehl-Avrami equation.

Unusual and highly tunable missing-linker defects in zirconium metal-organic framework UiO-66 and their important effects on gas adsorption.

UiO-66 is a highly important prototypical zirconium metal-organic framework (MOF) compound because of its excellent stabilities not typically found in common porous MOFs. In its perfect crystal structure, each Zr metal center is fully coordinated by 12 organic linkers to form a highly connected framework. Using high-resolution neutron power diffraction technique, we found the first direct structural evidence showing that real UiO-66 material contains significant amount of missing-linker defects, an unusual phenomenon for MOFs. The concentration of the missing-linker defects is surprisingly high, ∼10% in our sample, effectively reducing the framework connection from 12 to ∼11. We show that by varying the concentration of the acetic acid modulator and the synthesis time, the linker vacancies can be tuned systematically, leading to dramatically enhanced porosity. We obtained samples with pore volumes ranging from 0.44 to 1.0 cm(3)/g and Brunauer-Emmett-Teller surface areas ranging from 1000 to 1600 m(2)/g, the largest values of which are ∼150% and ∼60% higher than the theoretical values of defect-free UiO-66 crystal, respectively. The linker vacancies also have profound effects on the gas adsorption behaviors of UiO-66, in particular CO2. Finally, comparing the gas adsorption of hydroxylated and dehydroxylated UiO-66, we found that the former performs systematically better than the latter (particularly for CO2) suggesting the beneficial effect of the -OH groups. This finding is of great importance because hydroxylated UiO-66 is the practically more relevant, non-air-sensitive form of this MOF. The preferred gas adsorption on the metal center was confirmed by neutron diffraction measurements, and the gas binding strength enhancement by the -OH group was further supported by our first-principles calculations.

Mechanistic investigation on the formation and dehydrogenation of calcium amidoborane ammoniate.

Possessing high H(2) capacities and interesting dehydrogenation behavior, metal amidoborane ammoniates were prepared by reacting Ca(NH(2) )(2) , MgNH, and LiNH(2) with ammonia borane to form Ca(NH(2) BH(3) )(2) ⋅2 NH(3) , Mg(NH(2) BH(3) )(2) ⋅NH(3) , and Li(NH(2) BH(3) )(2) ⋅NH(3) (LiAB⋅NH(3) ). Insight into the mechanisms of amidoborane ammoniate formation and dehydrogenation was obtained by using isotopic labeling techniques. Selective (15) N and (2) H labeling showed that the formation of the ammoniate occurs via the transfer of one H(N) from ammonia borane to the [NH(2) ](-) unit in Ca(NH(2) )(2) giving rise to NH(3) and [NH(2) BH(3) ](-) . Supported by theoretical calculations, it is suggested that the improved dehydrogenation properties of metal amidoborane ammoniates compared to metal amidoboranes are a result of the participation of a strong dihydrogen bond between the NH(3) molecule and [NH(2) BH(3) ](-) . Our study elucidates the reaction pathway involved in the synthesis and dehydrogenation of Ca(NH(2) BH(3) )(2) ⋅2 NH(3) , and clarifies our understanding of the role of NH(3) , that is, it is not only involved in stabilizing the structure, but also in improving the dehydrogenation properties of metal amidoboranes.

Monoammoniate of calcium amidoborane: synthesis, structure, and hydrogen-storage properties.

The monoammoniate of calcium amidoborane, Ca(NH(2)BH(3))(2)·NH(3), was synthesized by ball milling an equimolar mixture of CaNH and AB. Its crystal structure has been determined and was found to contain a dihydrogen-bonded network. Thermal decomposition under an open-system begins with the evolution of about 1 equivalent/formula unit (equiv.) of NH(3) at temperatures <100 °C followed by the decomposition of Ca(NH(2)BH(3))(2) to release hydrogen. In a closed-system thermal decomposition process, hydrogen is liberated in two stages, at about 70 and 180 °C, with the first stage corresponding to an exothermic process. It has been found that the presence of the coordinated NH(3) has induced the dehydrogenation to occur at low temperature. At the end of the dehydrogenation, about 6 equiv. (∼ 10.2 wt %) of hydrogen can be released, giving rise to the formation of CaB(2)N(3)H.

Hydrogen sorption from the Mg(NH2)2-KH system and synthesis of an amide-imide complex of KMg(NH)(NH2).

The interaction between KH and Mg(NH(2))(2) is investigated. Results from temperature-programmed desorption measurements on samples of [Mg(NH(2))(2)][KH](x) (x=0.5, 1.0, and 2.0) indicated that dehydrogenation from [Mg(NH(2))(2)][KH] occurred through a two-step reaction with an onset temperature as low as 60 °C. Accompanied by hydrogen release, K(2)Mg(NH(2))(4) and MgNH successively developed at lower temperatures, whereas KMg(NH)(NH(2)) developed at higher temperatures. However, when dehydrogenation was conducted under isothermal and near-equilibrium conditions, a single-step reaction that led to the formation of KMg(NH)(NH(2)) was observed. KMg(NH)(NH(2)) is a new amide-imide complex. The synthesis of KMg(NH)(NH(2)) can be achieved either by dehydrogenation of the [Mg(NH(2))(2)][KH] mixture or by thermal decomposition of the [K(2)Mg(NH(2))(4)][Mg(NH(2))(2)] mixture.

Development of amidoboranes for hydrogen storage.

With high hydrogen content and moderate dehydrogenation conditions, metal amidoboranes have been regarded as potential hydrogen storage candidates and have attracted increasing attention recently. In this review we provide a practical introduction to the recent progress on the syntheses, crystal structures and dehydrogenation properties of metal amidoboranes and their derivatives.

Synthesis, structure and dehydrogenation of magnesium amidoborane monoammoniate.

Magnesium amidoborane monoammoniate (Mg(NH(2)BH(3))(2) x NH(3)) which crystallizes in a monoclinic structure (space group P2(1)/a) has been synthesized by reacting MgNH with NH(3)BH(3). Dihydrogen bonds are established between coordinated NH(3) and BH(3) of [NH(2)BH(3)](-) in the structure, promoting stoichiometric conversion of NH(3) to H(2).

Interaction of lithium hydride and ammonia borane in THF.

The two-step reaction between LiH and NH(3)BH(3) in THF leads to the production of more than 14 wt% of hydrogen at 40 degrees C.