Activation Energy For Desorption Research Articles

Boosting the de-/rehydrogenation properties of MgH2 with the addition of BaCoF4

In this study, the effect of barium cobalt fluoride (BaCoF4) on the de-/rehydrogenation properties of magnesium hydride (MgH2) was investigated for the first time. It was found that the 10 wt% BaCoF4-added MgH2 sample began to release hydrogen at 265 °C, which was about 75 °C lesser than the post-milled MgH2. Regarding dehydrogenation kinetic, the BaCoF4-added MgH2 composite rapidly released hydrogen 50 times faster than post-milled MgH2. The BaCoF4-added MgH2 sample released approximately 5.0 wt% within 30 min of dehydrogenation at 300 °C, whereas the post-milled MgH2 only released approximately 0.1 wt% hydrogen. Furthermore, the BaCoF4-added MgH2 sample obtained a hydrogen absorption capacity of 6.4 wt% in 5 min at 300 °C. In comparison, post-milled MgH2 absorbed only 5.5 wt% hydrogen in 5 min at 300 °C. Moreover, the addition of 10 wt% of BaCoF4 reduced the activation energy for the hydrogen desorption of MgH2 to 100.0 kJ/mol compared with 130.0 kJ/mol for the post-milled MgH2. The addition of BaCoF4 is believed to improve the hydrogen storage properties of MgH2 through the formation of the CoF3 and Ba or Ba-containing species during the dehydrogenation process, which plays a substantial role in lowering the desorption temperature and improves the sorption kinetics of MgH2.

Hydrangea-like NiO@KNbO3 as catalyst doping for MgH2: Boosting hydrogen storage performance

MgH2 is regarded as one of the most favorable materials for hydrogen storage caused by its safety, high efficiency, considerable capacity for storing hydrogen, and low cost. However, the application of this material is limited owing to subpar thermodynamics and kinetics, which can be improved via combination with other materials. A hydrangea-like NiO@KNbO3 was prepared by solvent thermal, hydrothermal, and calcination methods. Then, different amounts of NiO@KNbO3 (3, 5, 7, and 10 wt %) were added to MgH2 using ball-milling. MgH2 composite material doped with 5 wt % NiO@KNbO3 exhibits the most superior hydrogen storage performance, with a hydrogen absorption capacity of 4.95 wt % H2 within 5 min at 150 ℃ and 1.5 MPa H2 pressure. Furthermore, H2 release started approximately at 175 °C with 5.96 wt % H2 at 300 °C. The composite's H2 desorption activation energy was decreased to 71.75 kJ/mol. The Mg2NiH4/Mg2Ni generated in situ can serve as a "hydrogen pump" by creating numerous activation sites and pathways for hydrogen diffusion, thereby facilitating H2 dissociation during the process of hydrogen absorption. Additionally, the NiO@KNbO3-doped MgH2 samples exhibited excellent integrated hydrogen storage properties due to the combined effect of KNbO3 and the in situ formed NbO. The study provides clear evidence that NiO@KNbO3, a bimetallic oxide, can effectively enhance the hydrogen storage performance of MgH2 as an additive. Furthermore, the straightforward synthesis of NiO@KNbO3 offers guidance for the development of high-performance oxide catalysts that can improve the properties of MgH2.

Hydrogen Release and Uptake of MgH2 Modified by Ti3CN MXene

MgH2 has a high hydrogen content of 7.6 wt% and possesses good reversibility under normal conditions. However, pristine MgH2 requires a high temperature above 300 °C to release hydrogen, with very slow kinetics. In this work, we utilized Ti3CN MXene to reduce the operating temperature and enhance the kinetics of MgH2. The initial temperature of MgH2 decomposition can be lowered from 322 °C for pristine MgH2 to 214 °C through the employment of Ti3CN. The desorbed MgH2 + 7.5 wt% Ti3CN can start absorption at room temperature, while the desorbed pristine MgH2 can only start absorption at 120 °C. The employment of Ti3CN can significantly improve the hydrogen release kinetics of MgH2, with the desorption activation energy decreasing from 121 to 80 kJ mol−1. Regarding thermodynamics, the desorption enthalpy changes of MgH2 and MgH2 + 7.5 wt% Ti3CN were 79.3 and 78.8 kJ mol−1, respectively. This indicates that the employment of Ti3CN does not alter the thermal stability of MgH2. Phase evolution studies through the use of X-ray diffraction and electron diffraction both confirm that Ti3CN remains stable during the hydrogen release and uptake process of the composite. This work will help understand the impact of a transition metal carbonitride on the hydrogen storage of MgH2.

Enhancement of the Desorption Properties of LiAlH4 by the Addition of LaCoO3.

The high hydrogen storage capacity (10.5 wt.%) and release of hydrogen at a moderate temperature make LiAlH4 an appealing material for hydrogen storage. However, LiAlH4 suffers from slow kinetics and irreversibility. Hence, LaCoO3 was selected as an additive to defeat the slow kinetics problems of LiAlH4. For the irreversibility part, it still required high pressure to absorb hydrogen. Thus, this study focused on the reduction of the onset desorption temperature and the quickening of the desorption kinetics of LiAlH4. Here, we report the different weight percentages of LaCoO3 mixed with LiAlH4 using the ball-milling method. Interestingly, the addition of 10 wt.% of LaCoO3 resulted in a decrease in the desorption temperature to 70 °C for the first stage and 156 °C for the second stage. In addition, at 90 °C, LiAlH4 + 10 wt.% LaCoO3 can desorb 3.37 wt.% of H2 in 80 min, which is 10 times faster than the unsubstituted samples. The activation energies values for this composite are greatly reduced to 71 kJ/mol for the first stages and 95 kJ/mol for the second stages compared to milled LiAlH4 (107 kJ/mol and 120 kJ/mol for the first two stages, respectively). The enhancement of hydrogen desorption kinetics of LiAlH4 is attributed to the in situ formation of AlCo and La or La-containing species in the presence of LaCoO3, which resulted in a reduction of the onset desorption temperature and activation energies of LiAlH4.

Determination of kinetic characteristics of molecule thermodesorption on the surface of oxidated molybdenum

AbstractAdsorption and surface ionization (SI) of morphine molecules С17Н19NО3 with (m/z 285) on the surface of oxidized molybdenum was studied by voltage modulation method (VMM) with a high‐vacuum mass spectrometric setup using a “black chamber” with all walls cooled with liquid nitrogen. The SI mass spectra and temperature dependences of ion current of C9H7N+CH3 radical with m/z 144 were obtained by ionization of morphine molecules on the surface of oxidized molybdenum by using stationary SI method. They correspond to the previous results obtained by ionization of the same molecules on the surface of oxidized tungsten. The new peaks in the mass spectra can be explained by the catalytic properties of molybdenum. The sublimation heat and SI coefficient of C9H7NCH3 radicals with m/z 144 was determined. The rate constants K+ and activation energy E+ for radical ions C9H7N+CH3 with m/z 144 were determined in the adsorption of morphine molecules. For the first time the rate constants K0 and activation energies of thermal desorption Е° for radicals C9H7N+CH3 with m/z 144 during adsorption of morphine molecules were determined on the surface of oxidized molybdenum with a break of (C − C1)β bonds with the formation of ionized radicals by SI. The dependences LnΔ(ti) = f(t) obtained by the VMM for all temperatures of experiments were well approximated by straight lines and made it possible, from the slope of the graphs, to calculate the average lifetimes due to the processes of dissociative SI of morphine molecules on the surface. The ionization potential of this radical was estimated. It was found that the heats of desorption weakly depend on the nature of the surface itself, therefore, in theoretical energy calculations, the Lenard‐Johnson model can be used.

Hydrogen storage thermodynamics and kinetics of the as-cast and milled Ce-Mg-Ni-based alloy

Aiming at investigating the improvement of hydrogen storage performance of the ternary Ce5Mg85Ni10 alloy after mechanical ball milling, the phase transformation and microstructure evolution of the milled alloys are observed by XRD, SEM and TEM. After ball milling, the alloys mainly exhibit nanocrystalline and amorphous structures and consist of Mg, Mg2Ni and CeMg12 phases. After hydrogen absorption, the milled alloys consist of MgH2, Mg2NiH4 and CeH2.73 phases. Isothermal and non-isothermal reaction curves of hydrogen absorption and desorption of the milled alloys are characterized by an Sievert apparatus, DSC and TGA. The Arrhenius and Kissinger equations are used to calculate the hydrogen desorption activation energy. For the Ce5Mg85Ni10 alloy, its structure and thermodynamics and kinetics performance of hydrogen storage strongly depend on the ball milling time. The results shows that ball milling for 5 h can achieve the optimal activation and kinetics performances but further prolonging the ball milling time lead to the impairment of hydrogen storage performance. Besides, ball milling time has little effect on thermodynamic property. Experiments results show that the 5 h-milled alloy after activation can absorb 4 wt% H2 in 18 s at 473 K and 3 MPa, and can desorb 3 wt% H2 in 906 s at 533 K and 1 × 10−4 MPa. In addition, the hydrogen desorption enthalpy change of the 5 h-milled alloy is 75.28 kJ/mol and the hydrogen desorption apparent activation energy of this alloy is 62.69 kJ/mol.

Improved hydrogen storage thermodynamics and kinetics of La–Ce–Mg–Ni alloy by ball milling

Reducing particle size and modifying surface state by ball milling are recognized as a useful method to improve the hydrogen absorption kinetics of Mg-based alloys. In order to obtain amorphous and nanocrystalline structures, ball milling was used to process the as-cast La7Ce3Mg80Ni10 alloy ingot. The effects of ball milling time (5–30 h) on the structures and the thermodynamics and kinetics of hydrogen absorption/desorption of the as-milled alloys were studied. The XRD, SEM and TEM were applied to investigate the structure of the alloys. The Sievert apparatus, DSC and TGA were applied to study the isothermal and non-isothermal properties of hydrogen absorption/desorption. The Arrhenius and Kissinger methods were used to calculate the activation energy of hydrogen desorption. The results indicate that the 10 h-milled alloy has the optimal activation performance and hydrogen absorption/desorption kinetics. Prolonging or shortening the ball milling time results in the impaired hydrogen storage properties. The 10 h-milled alloy in fully activation state can absorb 4 wt% H2 in 80 s at 473 K and 3 MPa, and it can desorb 3 wt% H2 in 191 s at 573 K and 1 × 10−4 MPa. The hydrogen desorption enthalpy (ΔH) of the 10 h-milled alloy is 74.21 kJ/mol. Moreover, the 10 h-milled alloy has the smallest apparent activation energy for hydrogen desorption (62.9 kJ/mol), which is the reason why it has the optimal hydrogen storage properties.

High catalytic activity derived from TiNbAlC MAX towards improving the hydrogen storage properties of MgH2

MXenes are great catalysts for MgH2 hydrogen storage material. Nevertheless, the synthesis of MXenes needs a large quantity of corrosive HF solution to remove the Al layers from the MAX materials, which is harmful to the environment. In this work, TiNbAlC MAX was employed without HF-treatment to tailor the hydrogen storage of MgH2. The MgH2 + 10 wt% TiNbAlC composite was prepared by ball milling. The addition of 10 wt% TiNbAlC greatly reduces the onset temperature of MgH2 desorption from 332 °C to 197 °C. The composite can desorb 6.2 wt% of H2 in 10 min at a constant temperature of 300 °C. Moreover, the dehydrided MgH2 + 10 wt% TiNbAlC composite can start to absorb hydrogen at room temperature under a H2 pressure of 6 MPa. The hydrogen desorption activation energy of the composite was calculated by Kissinger’s method to be 101 kJ mol−1. Microstructures studies demonstrated that TiNbAlC will partially react with MgH2/H2 to form TiH1.971, which can act as a “hydrogen pump” to facilitate the hydrogen sorption of MgH2. This work suggests that MAX materials are good catalysts for hydrogen storage of MgH2 and provides new insight into the role of MAX phase in tailoring the hydrogen storage of Mg-based hydrogen storage materials.

Phase Transformation and Performance of Mg-Based Hydrogen Storage Material by Adding ZnO Nanoparticles.

ZnO nanoparticles in a spherical-like structure were synthesized via filtration and calcination methods, and different amounts of ZnO nanoparticles were added to MgH2 via ball milling. The SEM images revealed that the size of the composites was about 2 μm. The composites of different states were composed of large particles with small particles covering them. After the absorption and desorption cycle, the phase of composites changed. The MgH2-2.5 wt% ZnO composite reveals excellent performance among the three samples. The results show that the MgH2-2.5 wt% ZnO sample can swiftly absorb 3.77 wt% H2 in 20 min at 523 K and even at 473 K for 1 h can absorb 1.91 wt% H2. Meanwhile, the sample of MgH2-2.5 wt% ZnO can release 5.05 wt% H2 at 573 K within 30 min. Furthermore, the activation energies (Ea) of hydrogen absorption and desorption of the MgH2-2.5 wt% ZnO composite are 72.00 and 107.58 KJ/mol H2, respectively. This work reveals that the phase changes and the catalytic action of MgH2 in the cycle after the addition of ZnO, and the facile synthesis of the ZnO can provide direction for the better synthesis of catalyst materials.

Hydrogen absorption-desorption properties and hydrolysis performance of MgH2-Zr3V3O0.6Hx and MgH2-Zr3V3O0.6Hx-C composites

In this work, the catalytic effect of additions of η-Zr3V3O0.6 mixed suboxide and the title intermetallic composite with graphite on the properties of MgH2 in the processes of hydrogen storage and hydrogen generation has been studied. The hydride composites were obtained by high-energy reactive ball milling (RBM). The samples were characterized by X-ray diffraction and scanning electron microscopy. The cycling performance of hydrogen desorption and absorption as well as hydrogen generation in the hydrolysis reaction were studied. We found that during the reactive ball milling the studied composites are able in a few minutes to absorb ∼6.5 wt% of hydrogen. The addition of Zr3V3O0.6 and Zr3V3O0.6 + С catalysts not only increases the rates of hydrogen absorption and release, but also lowers the activation energy and the temperature of hydrogen desorption. For a composite containing 10 wt% of suboxide and 3 wt% of graphite, the activation energy of hydrogen desorption determined by the Kissinger method was very low, just 58 kJ/mol, and this value is among the lowest described in the reference publications. We also show that the intermetallic additive forms the Zr3V3O0.6H∼10 hydride, which results in a higher gravimetric capacity of the composite as H storage material. The improved kinetics of hydrogen exchange and increased hydrogenation capacity at modest operating temperatures of 150–200 °C appear to be characteristic for the composites containing suboxide and graphite additions. The reason for the advanced performance is in the different the morphology of the synthesized samples, particularly the graphite-containing composites showing a more developed dispergation of the material (the fraction with a particle size of 1–3 μm is >80 wt%). We furthermore show that the synthesized materials can be used in the hydrolysis process resulting in hydrogen generation. The amount of hydrogen released from the hydride Mg-Zr3V3O0.6-C composite in the hydrolysis reaction reaches 1364 ml/g (the conversion degree is ∼85 % for the process duration of 120 min) when using 0.04 M MgCl2 solutions.

High efficiency of toluene Ad-/Desorption on Thermal-conductive HKUST-1@BN nanosheets composite

Improving the adsorption capacity of the volatile organic compounds (VOCs) will inevitably decrease the desorption efficiency and hence increase more energy-consumption, which has become a crucial challenging problem for MOFs modification and composition toward VOCs adsorption. Herein, a thermal-conductive composition strategy was proposed to anchor BN nanosheets (BNNS) into HKUST-1 crystals via “N/O-Cu-O” interface. The formed HKUST-1@BNNS composite maintained high surface area (1633.7 m2/g having more microporous) and enhanced heat diffusivity (1.8 times of HKUST-1), simultaneously. This enabled significant increase of toluene adsorption capacity on HKUST-1@BNNS up to 4.3 mmol/g (2.8 times of HKUST-1) at ultra-low pressure (P/P0 ≈ 0.001) and higher desorption rate of toluene (kds = 29.3 × 10−2, 4.0 times of HKUST-1) with lower desorption activation energy (Ed = 33.5 kJ/mol). Compared with many other state-of-the-art adsorbents (e.g., MOFs, zeolites and activated carbons), it has a much higher adsorption capacity and regeneration rate. Thus, thermal-conductive MOFs construction can be deemed as smart strategy to enhance adsorption efficiency and save desorption energy for VOCs capture.

Optimization of UiO-66/CaCl2 composite material for thermal energy storage

Thermal energy storage technology can effectively solve the problems of mismatch between the supply and demand in solar thermal utilization. Injecting salt hydrates into porous matrices to develop composite materials could improve the thermal storage performance of pure salt hydrates. Recent studies have shown that UiO-66 could be a promising matrix of adsorption heat storage composite materials. In this paper, to optimize the UiO-66/CaCl2 composite material for thermal energy storage, a series of composite materials were prepared with injecting CaCl2 into UiO-66 of different crystal size and then characterized with various instruments. The results showed that the adsorption performance of the composites was determined by both the salt content and the crystal size of UiO-66. Among all the materials, it was found that U (100)-Ca30 had the best adsorption capacity, which was up to 1.80 g/g at 30 °C and 80% RH. The results of Kissinger equation fitting showed that the desorption activation energy of U (100)-Ca30 at low-temperature zone was lower than that of UiO-66. Moreover, the results showed that the thermal energy storage capacity of U (100)-Ca30 was up to 1416 J/g and it had also shown excellent stability with 16 times of cycling. All of the above results demonstrated that U (100)-Ca30 could be a potential candidate for adsorption thermal energy storage.

Hierarchical Structure Carbon-Coated CoNi Nanocatalysts Derived from Flower-Like Bimetal MOFs: Enhancing the Hydrogen Storage Performance of MgH2 under Mild Conditions

The construction of transition metal nanocatalysts has become an attractive way to improve the hydrogen storage performance of MgH2. However, it is still a great challenge to obtain multielement transition metal nanocatalysts, improve the hydrogen storage capacity of MgH2 under mild conditions (<573 K), and reduce the apparent activation energy of hydrogen absorption and desorption. In this work, a flower-like CoNi-MOF was successfully synthesized by sacrificing templates. After further pyrolysis, we obtained hierarchical structure flower-like MOF derivatives assembled by CoNi@C nanoparticles with an average particle size of 15.1 nm. Then, MgH2-x wt % CoNi@C nanocomposites are fabricated through the ball milling process. Due to the unique hierarchical flower-like structure of MOF derivatives, the inhibition of an amorphous carbon shell on CoNi alloy growth and agglomeration, and the synergistic catalysis of Mg2Co and Mg2Ni, the MgH2-10 wt % CoNi@C nanocomposite exhibits excellent hydrogen storage capacity under mild conditions and low apparent activation energy: At 473 K, the nanocomposite can quickly absorb 5.0 wt % H2 in 5 min, and even at 373 K, it can still absorb 4.2 wt % H2 in 60 min. At 573 and 548 K, it can release 4.8 and 3.1 wt % H2, respectively. The apparent activation energies for hydrogen absorption and desorption decrease remarkably to 24.9 and 67.3 kJ/mol, respectively, which are significantly better than those for MgH2-10 wt % Co@C (44.7 and 79.8 kJ/mol) and MgH2-10 wt % Ni@C (39.0 and 78.9 kJ/mol) nanocomposites. The first-principles calculation indicated that the hydrogen adsorption energy of the Mg–CoNi model is as low as −5.87 eV. This work provides a new strategy for the design of highly efficient multielement transition metal hydrogen storage material catalysts with a hierarchical structure.

The quantitative study of methane adsorption on the Pt(997) step surface as the initial process for reforming reactions

The adsorption states and thermal process of methane on a stepped Pt surface were investigated using temperature-programmed desorption (TPD), infrared reflection absorption spectroscopy (IRAS), and density functional theory (DFT) calculations including van der Waals interactions. By estimating the activation energies of methane desorption from the TPD data, it was revealed that the adsorption energy for methane on the step site (0.19 eV) was higher than that on the terrace site (0.15 eV). The IRAS spectrum after multilayer adsorption and subsequent 70 K heating showed two peaks at 3009 and 1305 cm−1, which were assigned to the antisymmetric stretching and the deformation modes for adsorbed methane on the step site, respectively. The present DFT calculations show that the most stable adsorption structure for methane on the step site is a “2H” structure, where two C-H bonds point toward Pt atoms. Based on the electronic structure analysis, we conclude that the stability of the 2H structure originates from the mixing between the methane molecular orbitals and the orbitals of step Pt atoms. As a result, the length of the C-H bond pointing toward the Pt step atom is elongated compared with that of other C-H bonds. Thus, the Pt step site already activates the adsorbed methane slightly.

Hydrogen trapping and hydrogen embrittlement (HE) susceptibility of X70 grade high-strength, acid-resistant, submarine pipeline steel with Mg treatment

The hydrogen embrittlement (HE) susceptibility of X70 grade, Acid-resistant, submarine pipeline steel with Mg treatment was studied via constant loading and slow strain rate tension (SSRT). The hydrogen diffusion and trapping behaviour in the tested steels treated with different Mg content was analysed by electrochemical hydrogen permeation testing and thermal desorption spectroscopy (TDS). The results suggested that micro/nanocomposite inclusions with “core-shell” structures obtained via Mg treatment have a greater activation energy of hydrogen desorption. On the one hand, this kind of inclusions can trap more hydrogen and reduce the diffusion coefficient of hydrogen in steel; on the other hand, the internal rigid core of Al–Mg–Ti–O and external soft shell of MnS not only play a role in stress shielding but also hinder the initiation and expansion of stress cracks. For the X70 grade high-strength, acid-resistant submarine pipeline steel, an optimal Mg addition amount is 0.003% (mass fraction).

Influence of mineral species on oil–soil interfacial interaction in petroleum-contaminated soils

The mineral species in soils vary in a wide variety of places, thus resulting in the petroleum-contaminated soil (PCS) with complex characters. Thus, the research on the effect of mineral species on oil-soil interactions in PCS takes on a critical significance. In this study, the desorption and adsorption behaviors of aromatic hydrocarbons (Ar) on two minerals surfaces were examined. Meanwhile, the interfacial forces between minerals and Ar were studied and the sources of these forces were analyzed. Moreover, molecular dynamics (MD) simulations were conducted to gain insight into the interfacial interaction mechanisms. As revealed by the results of this study, in comparison with Qs–Ar (quartz sand, Qs), Mnt–Ar (montmorillonite, Mnt) contaminants required higher temperature and activation energies for thermal desorption (201.95 kJ·mol−1vs. 127.82 kJ·mol−1). The above difference was generated since the adhesive forces between Ar and Mnt surfaces were greater than those between Ar and Qs. As indicated by the analysis of the adhesion force sources, the van der Waals forces were responsible for facilitating oil adhesion to mineral surfaces, even though the electrostatic force prevented oil–mineral adhesion. Furthermore, the hydrophobic forces facilitated adhesion in 3 nm. The MD results demonstrated that compared with the Qs system, there existed larger binding energies between Ar and Mnt, a lower diffusion coefficient for Ar on the Mnt surface, as well as more significant adsorption of Ar on Mnt. In general, the different mineral species affect the strength of the interaction at the oil–soil interface, which is a guideline for proposing targeted oil-soil separation measures.

Synergy of inside doped metals‒Outside coated graphene to enhance hydrogen storage in magnesium-based alloys

Grain growth of magnesium (Mg) and its hydride is one of the main reasons for kinetic and capacity degradation during the hydrogen absorption and desorption cycles. To solve this problem, herein we propose a novel method involving synergistic effect of inside embedded metals and outside coated graphene to limit the growth of Mg and its hydride grains. The graphene coated Mg‒Y‒Al alloys were selected as a model system for demonstrating this positive effect where the Mg91Y3Al6 alloy was first prepared by rapidly solidified method and then high-pressure milled with 5 wt% graphene upon 5 MPa hydrogen gas for obtaining in-situ formed YAl2 and YH3 embedded in the MgH2 matrix with graphene shell (denoted as MgH2-Y-Al@GR). In comparison to pure MgH2, the obtained MgH2-Y-Al@GR composites deliver much better kinetics and more stable cyclic performance. For instance, the MgH2-Y-Al@GR can release about 6.1 wt% H2 within 30 min at 300°C but pure MgH2 only desorbs ∼1.5 wt% H2. The activation energy for desorption of MgH2-Y-Al@GR samples is calculated to be 75.3±9.1 kJ/mol that is much lower than approximately 160 kJ/mol for pure MgH2. Moreover, its capacity retention is promoted from ∼57% of pure MgH2 to ∼84% after 50th cycles without obvious particle agglomeration and grain growth. The synergistic effect of outside graphene coating with inside embedded metals which could provide a huge number of active sites for catalysis as well as inhibit the grain growth of Mg and its hydride is believed to be responsible for these.

Flexible textural design of ZSM-5 zeolite adsorbent from coal fly ash via solvent-free method for toluene elimination

It is feasible and profitable to figure out multidiscipline environmental issues synergistically. Coal fly ash based adsorbent materials are widely used in the emission control of volatile organic compounds. A solvent-free method which was more environmental-friendly for ZSM-5 zeolites synthesis from coal fly ash was proposed to eliminate toluene. The results indicated that ZSM-5 zeolites were successfully synthesized from the precursor gel of coal fly ash with 30–60 wt% moisture contents. The SiO2/Al2O3 mole ratio of gel was up to 99 after the pretreatment of alkali roasting and acid precipitation. During the synthesis process, the appropriate Na2CO3-to-SiO2 ratio was 0.3, and the mesoporous formation would be facilitated along with the moisture content of gel. On the tendency of adsorption testing, the microporous structure was prone to the toluene adsorption, and the desorption was dependent on the mesoporous structure. The maximum adsorption capacity of 75.1 mg·g−1 was observed on S-40 sample, and the minimum desorption activation energy of 39.97 kJ·mol−1 was found on S-60 sample. The humid condition can reduce the toluene adsorption performance, and the maximum adsorption capacity was down to 63.7 mg·g−1. Additionally, the synthetic ZSM-5 zeolites still have some superiority in economics and ecology when compared with commercial zeolites. The novel synthesis method, preparing controllable ZSM-5 zeolites from coal fly ash with the advantages of low cost and environmental friendliness, exhibited the tremendous application potential in environmental field.

Enhanced hydrogen properties of MgH2 by Fe nanoparticles loaded hollow carbon spheres

In the present investigation, we have reported the synergistic effect of Fe nanoparticles and hollow carbon spheres composite on the hydrogen storage properties of MgH2. The onset desorption temperature for MgH2 catalyzed with hollow carbon spheres and Fe nanoparticle (MgH2-Fe-HCS) system has been observed to be 225.9 °C with a hydrogen storage capacity of 5.60 wt %. It could be able to absorb 5.60 wt % hydrogen within 55 s and desorb 5.50 wt % hydrogen within 12 min under 20 atm H2 pressure at 300 °C. The desorption activation energy of MgH2-Fe-HCS has been found to be 84.9 kJ/mol, whereas the desorption activation energies for as received MgH2, Hollow carbon sphere catalyzed MgH2 and Fe catalyzed MgH2 are found to be 130 kJ/mol, 103 kJ/mol, and 94.2 kJ/mol respectively. MgH2-Fe-HCS composite lowered the change in enthalpy of hydrogen desorption from MgH2 by 20.02 kJ/mol as compared to pristine MgH2. MgH2-Fe-HCS shows better cyclability up to 24 cycles of hydrogenation and dehydrogenation of MgH2. The mechanism for the better catalytic action of Fe and HCS on MgH2 has also been discussed.

Quantitative hydrogen trap states on high-angle grain boundaries and at dislocations in iron

Low-temperature thermal desorption spectrometry (L-TDS), by which specimens can be heated from -200 °C, was used to quantitatively evaluate the hydrogen desorption peak temperatures (Tp), the hydrogen desorption activation energies (Ea), and the hydrogen occupation ratios (θ) of high-angle grain boundaries and dislocations in iron. Cold-rolled iron was subjected to recrystallization and grain growth to produce three kinds of specimens with different areas of high-angle grain boundaries, in which low-angle grain boundaries were annihilated. L-TDS spectra of specimens containing dislocations and high-angle grain boundaries displayed two hydrogen desorption peaks, denoted as Peak 1 and Peak 2. Peak 1 corresponded to dislocations and displayed Tp, Ea, and θ values of 23 °C, 28.6 kJ·mol−1, and 1.1 to 2.7 atom·nm−1, respectively. In contrast, Peak 2 corresponded to high-angle grain boundaries and displayed Tp, Ea, and θ values of 85 °C, 43.7 kJ·mol−1, and 2.3 to 2.9 atom·nm−2, respectively.