Activation Energy For Desorption Research Articles

Multifactor orthogonal analysis on the desorption performances of P/N/S-doped activated carbon for acetone

As a widely used industrial material, the recovery of volatile organic compounds (VOCs) has great economic value and environmental significance. Improving the desorption performance of modified activated carbon in treating volatile organic compounds emissions is the key to the utilization of adsorbent and the recovery of adsorbate. In this study, five kinds of activated carbons and acetone were selected for orthogonal experiments to analyze the effect of multi-factors on the performances of major concern in engineering. The desorption process was divided into three zones, concentration fast rise zone, concentration fast decay zone and concentration slow decay zone, and quantitively evaluated for each zone. The results show that the enrichment ratio of SC800 is the highest in these sample, can reach 5.16, which is mainly affected by the chemical functional group with the highest adsorption energy, and is negatively correlated with the specific surface area. Combined the kinetic analysis and the quantitative evaluation of the total effects of chemical functional groups, the desorption rates are mainly related to the adsorbent surface saturation in the concentration fast decay zone and the total chemical effect in the concentration slow decay zone. In addition, the PC500 has the highest desorption efficiency of 69%, which can be measured by the desorption activation energy.

Activation Energy of Ion Desorption at Ionic Liquid/Pt Electrode Interfaces: A Sum-Frequency Generation Vibrational Spectroscopic Study.

Electrolyte/electrode interfaces of room-temperature ionic liquids (RTILs) exhibit hysteretic responses to different applied potentials owing to the differences in the ion adsorption/desorption processes; the ion desorption requires excess potential, which reflects the activation energy of ion desorption. Thus far, the contributions of the ion adsorption energy and the activation barrier for ion desorption toward the ion-dependent excess potential have not been quantified. Herein, we report on our infrared-visible sum-frequency generation vibrational spectroscopy study of the hysteretic responses of the anion adsorption/desorption at Pt electrode interfaces using neat, binary, and diluted RTILs composed of 1-butyl-3-methylimidazolium cations ([C4mim]+) and bis(trifluoromethanesulfonyl)amide ([TFSA]-) and trifluoromethanesulfonate ([OTf]-) anions. Experimental results are compared to the theoretical calculations for the electric double layer model. The hysteretic response of the RTIL/Pt interface derives predominantly from the activation energy of anion desorption, which causes the negative excess potential required for anion desorption. A comparison of the anion adsorption/desorption behaviors of neat RTILs with those of binary and diluted RTILs reveals that the large activation energy of anion desorption at the neat RTIL/Pt interface originates largely from the activation barrier for restructuring ionic layering in the diffuse layer.

Effect of Reinforcement Ratio and Particle Size on the Physical and Mechanical Performance of Epoxy Matrix Panels and Waste Wood from Iroko Chlorophora excelsa from Cameroon

The use of local materials developed from natural reinforcements remains a major challenge for many researchers in the development of the industry and the fight against pollution. The wood industry generates large quantities of environmental waste, including Iroko wood. To give Iroko a second life, this study uses Iroko sawdust waste to make an epoxy matrix composite material. The composite was produced using a cold pressing technique based on moving the top and bottom plates to a thickness of 10 mm. On this basis, three particle sizes [t < 0.35[, [0.35–0.63[, and [0.63–1[ were used, as well as three reinforcement (R)/matrix (M) percentages of 50R/50M, 60R/40M, and 70R/30M, where R is the reinforcement percentage and M is the matrix percentage. The physical tests, apparent and real density, porosity, moisture content, water absorption rate, absorption and desorption kinetics, diffusion theory, and activation energy were determined by the gravimetric method. A three-point bending test was carried out in accordance with the ASTM D790 for mechanical tests. The results show that the addition of Iroko particles lightens the material by reducing its density. The hydrophilic nature of Iroko particles increases the absorption rate and porosity, with good diffusion capacity as the particle size and percentage increase. The material produced can be light and porous, with possible applications in thermal insulation. In terms of kinetics, Verma et al.’s model best correlates the experimental desorption points for the 3 isotherms, while Page’s model best correlates the water absorption points. The mechanical results show that Young’s modulus and stress at break decrease with an increase in the reinforcement percentage and particle size. The mechanical results can be used to define the material’s applications in construction and furniture. In accordance with the EN312 standard, the composites produced can be classified as type 2 lightweight materials, suitable for use in dry and damp areas.

In-situ synthesis Al-fumarate on polyurethane foam as a monolithic desiccant for adsorption heat pump systems

Metal-organic framework (MOF) is considered the most promising adsorbent in adsorption heat pump (AHP) systems, owing to its high water-harvesting capacity and rapid adsorption kinetics. However, the practical implementation of powdery MOF usually suffers from poor recovery and easy agglomeration. In this work, a novel Al-fumarate loaded on polyurethane (PU) foam (PU/Al-fumarate) to construct a monolithic desiccant was designed using an in-situ synthetic self-assembly technology. Two synthesis strategies including mixed solvent thermal method (M method) and low-temperature solution method (L method) were implemented and compared. The influences of different synthesis methods on the MOF loading rate, crystal phase, chemical composition, pore structure, microscopic morphology, and the adsorption/desorption performance of monolithic desiccants were systematically discussed. The results showed that the two synthesis methods had no fundamental effects on the composition and crystal phase of PU/Al-fumarate. However, the M-method design strategy possessed a better MOF loading rate (71.76 %), higher specific surface area (722.15 m2·g−1), and more excellent water-adsorption capacity (0.333 g·g−1) as compared with the monolithic adsorbent synthesized by L-method technology. Furthermore, the resulting monolithic desiccant designed by the M-method strategy showed low desorption activation energy and good cyclic stability. Therefore, this novel PU foam-based Al-fumarate synthesized by M-method as monolithic desiccant will provide a potential candidate for AHP system.

Study on desorption characteristics of water vapor in fly ash concrete materials

In this paper, water vapor desorption tests are carried out on water-saturated concrete materials with different water-binder ratios and fly ash content. The desorption parameters are analyzed using the adsorption curve analysis method, which enables the acquisition of desorption characteristics for concrete materials. By utilizing the desorption isothermal curve, the desorption rate is calculated and further analysis is conducted on the influence of water-binder ratio and fly ash content on this rate. The results indicate that the desorption and activation energy for water vapor desorption in concrete materials is higher than the adsorption energy at the first layer, suggesting that removing water vapor from inner pore walls is more challenging than its adsorption. The amount of water vapor released from concrete materials follows a power function over time, as does the rate of desorption. Under conditions of relatively low ambient humidity, an increase in the water-binder ratio leads to a decrease in the rate of desorption. Conversely, under relatively high ambient humidity, an increase in the water-binder ratio results in an increased rate of desorption.

Insights into the role of VOCs properties on thermal desorption behaviors of two porous polymeric resins

Desorption is a critical process in the recovery or post-treatment of adsorbents saturated with volatile organic compounds (VOCs). In this study, the thermal desorption behaviors for eight VOCs on hypercrosslinked polymeric resin (HPR) and macroporous polymeric resin (MPR) were investigated through isothermal desorption and temperature programmed desorption (TPD). Compared with MPR, HPR with more micropores exhibited a lower desorption rate constant, lower desorption efficiency and higher desorption activation energy due to the strong binding energy generated between VOCs molecules and narrow micropores. As the polarizability of VOCs increased, the desorption rate constants on two porous polymeric resins decreased, while the desorption activation energy showed an incremental trend. Excellent linear correlations were observed between VOC polarizability and desorption rate constants (R2 = 0.957 for HPR and R2 = 0.940 for MPR) as well as between VOC polarizability and desorption activation energy (R2 = 0.981 for HPR and R2 = 0.969 for MPR). Furthermore, a polyparameter linear free energy relationship (PP-LFER) was developed to explore the influences of intermolecular interactions on desorption behaviors of VOCs on porous polymeric resins. The results indicated that the dispersive interaction, which is directly related to polarizability of VOCs, was the primary factor influencing the desorption activation energy of VOCs on porous polymeric resins. The find from this study helps evaluate fleetly and availably the desorption properties of VOCs based on their polarizability.

Desorption lifetimes and activation energies influencing gas–surface interactions and multiphase chemical kinetics

Abstract. Adsorption and desorption of gases on liquid or solid substrates are involved in multiphase processes and heterogeneous chemical reactions. The desorption energy (Edes0), which depends on the intermolecular forces between adsorbate and substrate, determines the residence time of chemical species at interfaces. We show how Edes0 and temperature influence the net uptake or release of gas species, the rates of surface–bulk exchange and surface or bulk reactions, and the equilibration timescales of gas–particle partitioning. Using literature data, we derive a parameterization to estimate Edes0 for a wide range of chemical species based on the molecular mass, polarizability, and oxygen-to-carbon ratio of the desorbing species independent of substrate-specific properties, which is possible because of the dominant role of the desorbing species' properties. Correlations between Edes0 and the enthalpies of vaporization and solvation are rooted in molecular interactions. The relation between Edes0 and desorption kinetics reflects the key role of interfacial exchange in multiphase processes. For small molecules and semi-volatile organics (VOC, IVOC, SVOC), Edes0 values around 10–100 kJ mol−1 correspond to desorption lifetimes around nanoseconds to days at room temperature. Even higher values up to years are obtained at low temperatures and for low volatile organic compounds (LVOC, ELVOC/ULVOC) relevant for secondary organic aerosols (SOA). Implications are discussed for SOA formation, gas–particle partitioning, organic phase changes, and indoor surface chemistry. We expect these insights to advance the mechanistic and kinetic understanding of multiphase processes in atmospheric and environmental physical chemistry, aerosol science, materials science, and chemical engineering.

Influence of Zr Addition on the Microstructure and Hydrogenation Kinetics of Ti50-xV25Cr25Zrx (x = 0, 5, 7, and 9) Alloys.

Due to the poor activation performance and kinetics of Ti50V25Cr25 alloys, the element Zr was added to improve the phase structure of the alloy and achieve a high-performance hydrogen storage alloy. The Ti50-xV25Cr25Zrx (x = 0, 5, 7, and 9) system alloys were prepared by arc melting. The alloys were analyzed using an X-ray diffractometer (XRD), scanning electron microscope (SEM), and differential scanning calorimeter (DSC). The hydrogen storage capabilities of the alloys were also obtained by the Sievert volumetric method. The results indicated that the alloy with Zr added had a combination of the C15 Laves phase and the BCC phase, whereas the Zr-free alloy had a BCC single phase. The partial replacement of Zr with Ti resulted in an increase in the lattice parameters of the main phase. The hydrogen storage kinetic performance and activation of the alloys both significantly improved with an increasing Zr concentration. The time to reach 90% of the maximum hydrogen storage capacity decreased to 2946 s, 230 s, and 120 s, respectively, with the increases in Zr concentration. The initial hydrogen absorption content of the alloys increased and then decreased after the addition of the element Zr. The second phase expanded with an increasing Zr concentration, which in turn decreased the abundance of the BCC main phase. The Ti43V25Cr25Zr7 alloy showed good cycle stability and hydrogen-desorption performance, and it could absorb 90% of the maximum hydrogen storage capacity in around 230 s. The maximum hydrogen-absorption capacity of the alloy was 2.7 wt%. The diffusion activation energy of hydrogen desorption dropped from 102.67 kJ/mol to 92.62 kJ/mol.

Efficient removal of dibutyl phthalate from transformer oils by iron/activated carbon adsorbent

Capturing dibutyl phthalate (DBP) impurities from transformer oils and purifying them is crucial for maintaining long-term sustainable transformer operation. Furthermore, this process significantly reduces the generation of waste from aged transformer oils, thereby contributing to environmental protection and sustainable development. In this study, various metal ion-modified wood activated carbons (ACs) were prepared using the wet impregnation method. The adsorption isotherms and adsorption kinetics studies reveal that Fe/AC exhibits a significant enhancement of more than 40% in DBP adsorption capacity compared to the original AC. Consequently, Fe/AC is the material with the highest adsorption capacity for DBP in transformer oils up to now. Furthermore, the desorption activation energy of DBP on Fe/AC was 46.623 kJ/mol, 1.73 times higher than original AC. Ultimately, the adsorption mechanism was explained using the Hard-Soft-Acid-Base (HSAB) principle, which demonstrated a stronger interaction between hard base DBP and Fe/AC due to the hard acidic nature of Fe3+ and therefore a higher capture capacity of DBP by Fe/AC. The simplified preparation method and enhanced adsorption capacity of the modified Fe/AC make it an efficient and cost-effective approach to ensure reliable and sustained transformer operation, while also minimizing the generation of waste transformer oils.

Exponential relaxation of the energy and desorption dynamics of atoms colliding with a surface

Atom–surface collisions are one of the most important topics in surface science. To further disclose the physical mechanism underlying atom–surface interaction at the microscopic level, we study the dynamics of an incident atom with a molecular dynamics simulation. Emphasis is put on the temporal evolutions of energy and residence times of the colliding atoms. The incident atoms experience two stages after colliding with the surface. First, the atoms relax to the equilibrium state in an exponential fashion. Then, the atoms become equilibrated with the surface and depart from the surface with a converged desorption rate. Two parameters are proposed to characterize the process: the characteristic energy relaxation time and the equilibrium residence time. At the relaxation stage, the desorption rate varies with the energy, and the probability distribution function (PDF) of the residence time obeys a power law. At the equilibrium state, the desorption rate is invariable, and the PDF of the residence time decays exponentially. We further find that the desorption rate for both stages can be calculated by a consistent Arrhenius equation, with the desorption activation energy and kinetic energy evolving with time in the relaxation stage. It appears that the gas–surface interaction dynamics can be explained by trapping-desorption theory in both the relaxation state and the equilibration state.

Improvement of the Hydrogen Storage Characteristics of MgH2 with Al Nano-Catalyst Produced by the Method of Electric Explosion of Wires.

A new composite with a core-shell structure based on magnesium hydride and finely dispersed aluminum powder with an aluminum oxide shell was mechanically synthesized. We used magnesium chips to produce magnesium hydride and aluminum wire after exploitation to produce nano-sized aluminum powder. The beginning of the hydrogen release from the composite occurred at the temperature of 117 °C. The maximum desorption temperature from the MgH2-EEWAl composite (10 wt.%) was 336 °C, compared to pure magnesium hydride-417 °C. The mass content of hydrogen in the composite was 5.5 wt.%. The positive effect of the aluminum powder produced by the electric explosion of wires method on reducing the activation energy of desorption was demonstrated. The composite's desorption activation energy was found to be 109 ± 1 kJ/mol, while pure magnesium hydride had an activation energy of 161 ± 2 kJ/mol. The results obtained make it possible to expand the possibility of using magnesium and aluminum waste for hydrogen energy.

Coverage-dependent desorption kinetics of water on a well-ordered alumina thin film surface.

We have developed an experimental and analytical setup for thermal desorption spectroscopy of solid water films on surfaces. We obtain the coverage-dependent desorption kinetics of water molecules from a well-defined ultra-thin alumina/NiAl(110) surface in the coverage range of 0-2 monolayers. We use a novel deconvolution technique to eliminate the pumping delay of water vapor in the vacuum system, which has previously hindered the accurate estimation of desorption kinetic parameters, such as activation energy and pre-exponential factor. The coverage-dependent Arrhenius analysis reveals that the desorption activation energy decreases with increasing coverage in the sub-monolayer range, indicating that the water-water interaction is not attractive. We also find that the pre-exponential factor for the second layer is higher than that for the sub-monolayer. We explain this difference in terms of transition state theory and propose that entropic effects play a significant role in water desorption kinetics.

Mechanistic and Kinetic Measurements of Elementary Surface Reactions Using Temperature-Programmed X-ray Photoelectron Spectroscopy.

This paper describes a method by which surface-reaction kinetics can be measured by slowly and precisely ramping up the surface temperature at a constant rate while simultaneously collecting X-ray photoelectron spectra (XPS). This approach results in the collection of a large amount of data over relatively small temperature steps to produce quasi-continuous kinetic data. The method is illustrated for the desorption and reaction of diethyl disulfide (DEDS) on a Au(111) substrate in ultrahigh vacuum, where the results can be compared with previous conventional temperature-programmed desorption (TPD) data from Au(111). Experiments were carried out using a double-pass cylindrical-mirror analyzer with a channeltron detector to demonstrate how this approach can be implemented in a routine, multitechnique vacuum chamber. The approach will be even more effective in a more modern, specialized XPS apparatus with high-transmission hemispherical analyzers with multichannel array detectors, which will enable the spectra of several elements to be measured simultaneously. The results yielded an activation energy for multilayer desorption of DEDS of 41 ± 1 kJ/mol, with a pre-exponential factor of 8 ± 7 × 1012 s-1, an activation energy of 53 ± 6 kJ/mol and pre-exponential factor of 9 ± 8 × 1013 s-1 for monolayer desorption and an activation energy of 90 ± 6 kJ/mol with a prefactor of 1.0 ± 0.3 × 1015 s-1 for the reaction of adsorbed ethyl thiolate species to adsorbed DEDS. While these results were collected for a system for which the kinetic data could have been obtained using conventional TPD, this method can be more usefully applied to those surface reaction processes that do not rely on the formation of desorption products. This system, having been previously studied by TPD, facilitates a comparison with results obtained by conventional methods.

Microstructure and hydrogen storage properties of the Mg2−xYxNi0.9Co0.1 (x = 0, 0.2, 0.3, and 0.4) alloys

Rare earth elements have excellent catalytic effects on improving hydrogen storage properties of the Mg2Ni-based alloys. This study used a small amount of Y to substitute Mg partially in Mg2Ni0.9Co0.1 and characterized and discussed the effects of Y on the solidification and de-/hydrogenation behaviors. The Mg2−xYxNi0.9Co0.1 (x = 0, 0.2, 0.3, and 0.4) hydrogen storage alloys were prepared using a metallurgy method. The phase composition of the alloys was studied using X-ray diffraction (XRD). Additionally, their microstructure and chemical composition were studied using scanning electron microscopy and energy-dispersive X-ray spectroscopy, respectively. The hydrogen absorption and desorption properties of the alloys were studied using pressure-composition isotherms and differential scanning calorimetric (DSC) measurements. The structure of the as-cast Mg2Ni0.9Co0.1 alloy was composed of the peritectic Mg2Ni, eutectic Mg–Mg2Ni, and a small amount of pre-precipitated Mg–Ni–Co ternary phases, and was converted into the Mg2NiH4, Mg2Ni0.9Co0.1H4, and MgH2 phases after hydrogen absorption. Furthermore, the XRD patterns of the alloys showed the MgYNi4 phase and a trace amount of the Y2O3 phase along with the Mg and Mg2Ni phases after the addition of Y. After hydrogen absorption, the phase of the alloys was composed of the Mg2NiH4, MgH2, MgYNi4, YH3, Y2O3, and Mg2NiH0.3 phases. With the increase of Y addition, the area ratios of the peritectic Mg2Ni matrix phase in the Mg2−xYxNi0.9Co0.1 (x = 0, 0.2, 0.3, and 0.4) alloys gradually decreased until they disappeared. However, the eutectic structure gradually increased, and the microstructures of the alloys were obviously refined. The addition of Y improves the activation performance of the alloys. The alloy only needed one cycle of de-/hydrogenation to complete the activation for x = 0.4. The DSC curves showed that the initial dehydrogenation temperatures of Mg2Ni0.9Co0.1 and Mg1.8Y0.2Ni0.9Co0.1 were 200 and 156 °C, respectively. The desorption activation energies of the hydrides of the Mg2Ni0.9Co0.1 and Mg1.8Y0.2Ni0.9Co0.1 alloys calculated using the Kissinger method were 94.7 and 56.5 kJ/mol, respectively. Moreover, the addition of Y reduced the initial desorption temperature of the alloys and improved their kinetic properties.

Downshift of the Ni d band center over Ni nanoparticles in situ confined within an amorphous silicon nitride matrix.

Herein, nanocomposites made of Ni nanoparticles in situ distributed in an amorphous silicon nitride (Ni/a-Si3N4) matrix, on the one hand, and within an amorphous silicon dioxide (Ni/a-SiO2) matrix, on the other hand, were synthesized from the same Ni-modified polysilazane precursor. In both compounds, the Ni/Si atomic ratio (0.06-0.07), average Ni nanocrystallite size (7.0-7.6 nm) and micro/mesoporosity of the matrix were rigorously fixed. Hydrogen (H2)-temperature-programmed desorption (TPD) profile analysis revealed that the activation energy for H2 desorption at about 100-130 °C evaluated for the Ni/a-Si3N4 sample (47.4 kJ mol-1) was lower than that for the Ni/a-SiO2 sample (68.0 kJ mol-1). Mechanistic study with X-ray photoelectron spectroscopy (XPS) analysis and density functional theory (DFT) calculations revealed that, at Ni nanoparticle/matrix heterointerfaces, Ni becomes more covalently bonded to N atoms in the a-Si3N4 matrix compared to O atoms in the a-SiO2 matrix. Therefore, based on experimental and theoretical studies, we elucidated that nickel-nitrogen (Ni-N) interactions at the heterointerface lead to remarkable Ni d band broadening and downshifting of the d band center relative to those generated by Ni-oxygen (Ni-O) interactions at the heterointerface. This facilitates H2 desorption, as experimentally observed in the Ni/a-Si3N4 sample.

Preparation of CPVC-based activated carbon spheres and insight into the adsorption-desorption performance for typical volatile organic compounds

Chlorinated polyvinyl chloride (CPVC)-based activated carbon spheres with smooth surfaces, good sphericity, interconnected hierarchical porous structure and high porosity have been synthesized by non-solvent induced phase separation method, followed by successive treatments of stabilization, carbonization at 450 °C in N2 atmosphere, and activation with CO2 as an agent at 900–1000 °C. The effect of activation temperatures on the textural properties of activated carbon spheres and their adsorption potential for volatile organic compounds (VOCs) under dynamic conditions is investigated. CO2 activation improves the hierarchy in the microporous range by stimulating the formation of supermicropores and significantly expands the specific surface area and pore volume of activated carbon spheres. The textural properties of adsorbents play a vital role in the adsorption performance of different VOCs. The adsorption capacity of VOC molecules can be greatly promoted by elevating specific surface area and pore volume. Due to the compatibility difference between the VOC molecules and the pore structure of adsorbents, the adsorption capacity follows the order of toluene > m-xylene > n-hexane. The adsorption isotherm of toluene on CPVC-AC1000 can be generally expressed by the Langmuir model. The adsorbents with larger average pore diameters possess a lower activation energy of desorption, which is beneficial for desorption. The carbon sphere activated at 1000 °C is a high-performance adsorbent with good reusability. Thus, the present study provides a synthesis process to produce the activated carbon spheres with high porosity from low-cost CPVC for its application in VOC adsorption.

Sn-doped n-type GaN layer with high electron density of 1020 cm−3 grown by halide vapor phase epitaxy

A Sn-doped n-type GaN layer with a high electron density of 2 × 1020 cm−3 and a low resistivity of 8.7 × 10−4 Ω∙cm was grown by halide vapor phase epitaxy (HVPE). Sn doping was performed through the reaction between Sn metal and HCl gas. The Sn concentration markedly increased with decreasing growth temperature and the activation energy of Sn desorption from the GaN surface was found to be 4.1 eV. Smooth surfaces were obtained by introducing the Sn precursor even though the samples were grown at a low temperature of 905 °C, suggesting that Sn atoms act as surfactants and promote the migration of Ga adatoms. Almost all the Sn atoms act as donors in GaN below the Sn concentration of 2 × 1020 cm−3. These results indicate that using the Sn donor is promising for fabricating low-resistivity n-type GaN substrates by HVPE.

Microstructure and hydrogen storage properties of MgH2/MIL-101(Cr) composite

In this paper, a new hydrogen storage composite based on magnesium hydride and metal-organic framework MIL-101(Cr) (an acronym for Material Institute Lavoisier) has been mechanically synthesized and investigated. The hydrogen sorption and desorption behavior in the composite was investigated for the temperature and pressure ranges of (593−653) K and (0−3) MPa, respectively. According to the pressure-composition-temperature isotherms of hydrogen sorption/desorption, the MgH2–5 wt%MIL-101(Cr) composite starts to absorb hydrogen at a lower pressure at 593 K. In addition, the hydrogen release peak for composite shifts to lower temperatures by about 140 K compared to the pure milled MgH2 during temperature programmed desorption at a heating rate of 6 K/min. The activation energy of hydrogen desorption from the composite is 120 ± 2 kJ/mol, which is 36% lower than the activation energy of hydrogen desorption from magnesium hydride (189 ± 2 kJ/mol). The enthalpy of hydrogen absorption was found to be 73 kJ/mol H2 and 60 kJ/mol H2 for milled MgH2 and MgH2–5 wt%MIL-101(Cr) composites, respectively. It is showed that the MIL-101(Cr) MOF structures decompose during ball milling and the chromium oxide nanoparticles form a core-shell structure with MgH2 particles. Thus, composite has better sorption and desorption properties than pure magnesium/magnesium hydride due to the nanoconfinement of MgH2. The chromium oxide nanoparticles act as active sites on the surface of the magnesium particles and facilitate the dissociative chemisorption or recombinative desorption of hydrogen. The main regularities of the phase transition in the magnesium-hydrogen system for the composite and magnesium hydride during dehydrogenation have been studied for temperatures in the range of 298–750 K. The in situ analysis of the phase transitions during the dehydrogenation of MgH2 and MgH2–5 wt%MIL-101(Cr) composite indicates a pronounced catalytic effect of the addition of MIL-101(Cr) to the Mg/MgH2. Based on the experimental results and ab initio calculations, a mechanism for the sorption and desorption of hydrogen by the composite has been proposed.

Synergistic enhancement of hydrogen storage performance of Mg-La-Ni alloy by CeO2@C composite catalyst

An enhanced chemical blowing carburation method was successfully employed to synthesize a CeO2@C composite catalyst. The catalyst comprises highly dispersed CeO2 nanoparticles within a porous carbon matrix, demonstrating a well-developed micropore structure, an ultrahigh specific surface area, and a high density of defects. Various amounts of CeO2@C were mechanically milled with an Mg96La3Ni alloy to investigate its hydrogen storage properties. The results demonstrated that incorporating CeO2@C significantly refined the Mg-based alloy, leading to an increase in both specific surface area and the number of active sites. The addition of CeO2@C greatly enhanced the hydrogen absorption and desorption kinetics of the alloy, with the optimal amount being 5 wt % CeO2@C. At 360 °C, the alloy could absorb 78.1% of its maximum hydrogen capacity within 2 min, and release an equal amount of hydrogen within 5 min, with the desorption activation energy decreasing to 107.33 kJ/mol H2. The incorporation of CeO2@C significantly reduced the desorption activation energy of the alloy while leaving its thermodynamic performance unaffected. The CeO2 nanoparticles and carbon matrix synergistically catalyze the reactions, with the former primarily facilitating nucleation and the latter facilitating hydrogen diffusion. This study offers novel insights into the design of magnesium-based hydrogen storage materials. The enhanced hydrogen storage performance demonstrated in this work shows the potential of CeO2@C modified Mg-based alloys for practical applications in hydrogen fuel cell vehicles, portable power sources, and other hydrogen energy storage systems.

Deep integration of pyrolysis kinetics and pyrolysis mechanism of polyimide aerogels

As novel advanced organic materials, polyimide aerogels (PI-AER) exhibit high porosity and excellent thermal stability. For the general and safe application of PI-AER, it is imperative to clarify their thermal decomposition process. The kinetic parameters of PI-ARE pyrolysis were calculated using different traditional kinetic methods, and the results showed that the PI-AER pyrolysis process conformed to the Fn-like mechanistic function model with an average activation energy of 143.984 kJ/mol. The pyrolysis mechanism function model of the main pyrolysis stages was optimized and reconstructed to obtain the optimal solution f(α). In addition, the concentration changes of pyrolysis products with increasing temperature were monitored by TG-MS and the PI-AER bond breaking mechanism was analyzed. Finally, the TG curves were fitted piecewise to obtain Ea and lnA for the two pyrolysis processes. Combined with the pyrolysis mechanism and two-stage kinetic parameter analysis, the effects of the two pyrolysis stages of PI-AER on the kinetic parameters were elucidated. It was shown that the activation energies of solvent volatilization and desorption and PI-AER main chain were 60.1 kJ/mol and 147.76 kJ/mol, respectively. This study provides fundamental industrial parameters for the application of polyimide aerogels in extreme conditions.