High-temperature Desorption Research Articles

A new method to quantify particulate sodium and potassium salts (nitrate, chloride, and sulfate) by thermal desorption aerosol mass spectrometry

Abstract. The reaction of sea salt (or biomass burning) particles with sulfuric acid and nitric acid leads to the displacement of chloride relative to sodium (or potassium). We have developed a new particle mass spectrometer to quantify non-refractory and refractory sulfate aerosols (referred to as refractory aerosol thermal desorption mass spectrometer: rTDMS). The combination of a graphite particle collector and a carbon dioxide laser enables high desorption temperature (blackbody equivalent radiation temperature of up to 930 ∘C). Ion signals originating from evolved gas molecules are detected by a quadrupole mass spectrometer. Here we propose a new method to quantify the mass concentrations of sodium nitrate (NaNO3: SN), sodium chloride (NaCl: SC), sodium sulfate (Na2SO4: SS), potassium nitrate (KNO3: PN), potassium chloride (KCl: PC), and potassium sulfate (K2SO4: PS) particles by using the rTDMS. Laboratory experiments were performed to test the sensitivities of the rTDMS to various types of particles. We measured ion signals originating from single-component particles for each compound and found a good linearity (r2>0.8) between the major ion signals and mass loadings. We also measured ion signals originating from internally mixed SN + SC + SS (or PN + PC + PS) particles and found that the temporal profiles of ion signals at m/z 23 (Na+) (or 39; K+) were characterized by three sequential peaks associated with the evolution of the desorption temperature. We tested potential interferences in the quantification of sea salt particles under real-world conditions by artificially generating “modified” sea salt particles from a mixture of diluted seawater and SN (or SS) solution. The SS/SC ratios estimated from the ion signals at m/z 23, 36 (H35Cl+), and 48 (SO+) agreed well with those predicted from the solution concentrations to within ∼10 %. The SN/SC ratios estimated from the ion signals at m/z 30 (NO+) and 36 also agreed with those predicted from the solution concentrations to within ∼15 %, whereas the SN/SC ratios estimated from m/z 23 were significantly lower than the predicted values. Based on these experimental results, the applicability of the rTDMS to ambient measurements of sea salt particles is discussed.

Formation of Complex Organic Molecules in Hot Molecular Cores through Nondiffusive Grain-surface and Ice-mantle Chemistry

Abstract A new, more comprehensive model of gas–grain chemistry in hot molecular cores is presented, in which nondiffusive reaction processes on dust-grain surfaces and in ice mantles are implemented alongside traditional diffusive surface/bulk-ice chemistry. We build on our nondiffusive treatments used for chemistry in cold sources, adopting a standard collapse/warm-up physical model for hot cores. A number of other new chemical model inputs and treatments are also explored in depth, culminating in a final model that demonstrates excellent agreement with gas-phase observational abundances for many molecules, including some (e.g., methoxymethanol) that could not be reproduced by conventional diffusive mechanisms. The observed ratios of structural isomers methyl formate, glycolaldehyde, and acetic acid are well reproduced by the models. The main temperature regimes in which various complex organic molecules (COMs) are formed are identified. Nondiffusive chemistry advances the production of many COMs to much earlier times and lower temperatures than in previous model implementations. Those species may form either as by-products of simple-ice production, or via early photochemistry within the ices while external UV photons can still penetrate. Cosmic ray-induced photochemistry is less important than in past models, although it affects some species strongly over long timescales. Another production regime occurs during the high-temperature desorption of solid water, whereby radicals trapped in the ice are released onto the grain/ice surface, where they rapidly react. Several recently proposed gas-phase COM-production mechanisms are also introduced, but they rarely dominate. New surface/ice reactions involving CH and CH2 are found to contribute substantially to the formation of certain COMs.

Mixed polyamines promotes CO2 adsorption from air

The deployment of large-scale direct air capture (DAC) technology relies on the development of energy-efficient and cost-effective CO2 capture materials. The high desorption temperature of the current DAC adsorbents, especially the supported polyamines, is undesirable. In this work, the "mixed-polyamines" concept was adopted to prepare class 1 adsorbents by impregnating both tetraethylenepentamine (TEPA) and diethanolamine (DEA) into the mesoporous SBA-15. The synergy of TEPA and DEA influences the reaction mechanism between CO2 and amines sites, resulting in higher amine efficiency and lower regeneration temperature. Moreover, CO2 adsorption and desorption kinetics are enhanced by the introduction of hydroxyl groups from DEA. The desorption process of solid polyamines-loaded adsorbents fits well with the Avrami model under ultra-dilute CO2 concentrations. SBA-15 loaded mixed polyamine with a weight ratio of TEPA to DEA equaling to 4 shows a maximum CO2 adsorption amount of 1.93 mmol/g at 400 ppm CO2 and 25 °C, a fast adsorption rate of 1.82 mmol/(g·h), and a desorption rate of 0.26 mmol/(g·min) at 80 °C within the first 5 min, which is believed to be a promising DAC adsorbent for practical application.

MgH2 confinement in MOF-derived N-doped porous carbon nanofibers for enhanced hydrogen storage

Magnesium hydride (MgH2) is one of the most promising hydrogen storage materials, while the high desorption temperature and sluggish kinetics hamper its further commercialization. Herein, a novel MOF-derived 1D N-doped hierarchically porous carbon nanofiber (pCNF) is firstly prepared and used as the scaffold for self-assembly of MgH2/Ni nanoparticles (NPs). The resultant MgH2/Ni@pCNF nanocomposites show faster desorption kinetics (Ea = 96.58 kJ/mol H2), lower onset desorption temperature (Tonset = 200 °C) when compare to the commercial MgH2 (Ea = 142.27 kJ/mol H2, Tonset = 350 °C). Moreover, hydrogen absorption can be achieved at a temperature as low as 100 °C with a capacity of 2.2 wt% within 120 min. Additionally, the composites exhibit excellent cycling stability with a capacity retention over 95.4% after 10 complete re-/dehydriding cycles at 300 °C. In-situ HRTEM observations of the desorption process combined with XPS and XRD indicate that the synergistic effects from nanoconfinement of Mg/MgH2 in pCNF, electron-donating ability of N atoms and the “hydrogen pump” function of Mg2Ni/Mg2NiH4 account for the unprecedent hydrogen storage properties. The strategy of using the MOF-derived 1D pCNF as support for nanoparticles provides a new approach for fabricating nanostructured energy materials with enhanced performances.

High-capacity reversible hydrogen storage in scandium decorated holey graphyne: Theoretical perspectives

We have investigated the hydrogen storage capabilities of scandium decorated holey graphyne, a recently synthesized carbon allotrope, by applying density functional theory and molecular dynamics simulations. We have observed that one unit cell of holey graphyne can adsorb 6 Sc atoms, and each Sc atom can adsorb up to 5H2 molecules with an average binding energy and average desorption temperature of −0.36 eV/H2 and 464 K, respectively. The gravimetric weight percentage of hydrogen is 9.80%, which is considerably higher than the Department of Energy, United-States requirements of 6.5%. We have found that a total amount of 1.9e charge transfers from the 3d and 4s orbitals of Sc atom to the C-2p orbitals of holey graphyne by performing the Bader charge analysis. Hydrogen molecules are bonded with the scandium atom by Kubas interactions. The ab-initio molecular dynamics simulations confirm the structural integrity of scandium decorated holey graphyne system at the high desorption temperatures. The presence of sufficient diffusion energy barriers for the Sc atom ensure the avoidance of metal-metal clustering in the system.

Fe-Co controlled super-hygroscopic hydrogels toward efficient atmospheric water harvesting.

Extracting atmospheric moisture for freshwater production is an appealing way to mitigate the global water crisis. However, the low moisture sorption capacity and high desorption temperature are the major bottlenecks for efficient atmospheric water harvesting. Herein, we develop a transition metal super-hygroscopic hydrogel by an economical strategy, which is constructed through a facile coordination between metal salts and ethanolamine. When the empty electron orbital of the metal ion is coordinated with the lone electron pair of nitrogen or oxygen atom, the water active sorption site is formed. A single water layer is bonded on the sites by a coordination effect, followed by physical interaction with water to form multi-layer structures. The Fe and Co ions in the hydrogel function as dual sorption sites to capture moisture, which can harvest additional water by the synergistic effect of bimetals. As a result, the bimetal hydrogel contributes to a high water uptake of 5.22 g g-1 at 95% RH, triggering the desorption process by one solar intensity due to its low desorption temperature (≤50 °C).

Adsorption/desorption characteristics of low-concentration semi-volatile organic compounds in vapor phase on activated carbon

The adsorption/desorption behaviors of semi-volatile organic compounds (SVOCs: 1,2,3,4-tetrachlorobenzene (TCB) and phenol) in vapor phase by activated carbon (AC) were investigated by the experiments and density functional theory calculation. Investigations showed that at 100–160 °C, the adsorption capacities of TCB and phenol on AC were in the range of 176.6–342.0 mg/g and 24.0–66.4 mg/g, respectively. Increasing the temperature inhibited the SVOCs adsorption. TCB tended to be adsorbed on AC surface by monolayer, whereas the phenol was multilayer adsorption. The stronger interaction between SVOCs and active sites resulted in a higher desorption temperature (TCB: 255–689 °C; phenol: 200–369 °C). The SVOCs adsorption on AC was fitted well by the pseudo-first-order kinetic model, their lower concentration and larger molecular structure influenced the AC external mass transfer and intraparticle diffusion. TCB and phenol were adsorbed on graphite layer by a parallel manner, their highest adsorption energies were −75.59 kJ/mol and −55.00 kJ/mol, respectively. Oxygen-containing groups altered the charge distribution of the atoms at the edge of the graphite layer, which improved the SVOCs adsorption through enhancement of electrostatic interactions and formation of hydrogen bonds. The carboxyl and lactone groups played a critical role in improving the TCB adsorption capacity, while the carboxyl was important for phenol adsorption.

Catalytic effect of NiO/C derived from Ni-UMOFNs on the hydrogen storage performance of magnesium hydride

Magnesium based solid hydrogen storage material (MgH2) has the advantages of good safety and high hydrogen storage capacity in the shipping field. However, the high hydrogen absorption and desorption temperature have not been well solved. Herein, this work proves that it is very effective to improve the hydrogen storage performance of MgH2 by doping nano NiO/C catalyst. Specifically, experimental results showed that MgH2 + 9 wt% NiO/C composite could dehydrogenate at 195 °C, which was 155 °C lower than pure MgH2. In addition, 6.21 wt% H2 could be released rapidly at 300 °C for 10 min. After complete dehydrogenation, the absorption rate of hydrogen is 50 °C, which is 80 °C lower than that of pure MgH2. Moreover, 5.13 wt% H2 could be absorbed within 1 h at 125 °C and 3 MPa hydrogen pressure. In addition, dehydrogenation and hydrogen absorption apparent activation energies of MgH2 + 9 wt% NiO/C composite are 70.26 kJ/mol and 25.55 kJ/mol lower than those of pure MgH2, respectively. The cycle experiment showed that MgH2 + 9 wt% NiO/C had excellent cycle stability and could maintain 98.8% hydrogen storage capacity after 20 cycles. Furthermore, the study of the catalytic mechanism indicated that NiO/C catalyst is evenly distributed on the surface of MgH2. More importantly, Mg2Ni/Mg2NiH4 is generated in situ, which acts as a "hydrogen pump" and speeds up hydrogen diffusion during the hydrogen absorption and desorption cycle.

Enhanced Hydrogen Storage Properties of LiAlH4 by Excellent Catalytic Activity of XTiO3@h‐BN (X = Co, Ni)

AbstractThe high desorption temperature and slow kinetics still restrict the applications of LiAlH4 in hydrogen storage. To solve the above problems, NiTiO3@h‐BN and CoTiO3@h‐BN prepared for the first time are introduced into LiAlH4 by ball milling. LiAlH4 doped with 7 wt% NiTiO3@h‐BN, selected as an optimal doping sample, starts to release hydrogen at 68.1 °C, and the total amount of hydrogen released is 7.11 wt% below 300 °C. The activation energies (Ea) of the two‐step hydrogen release reactions are 55.93 and 59.25 kJ∙mol−1, which are 45.8% and 69.0% lower than those of as‐received LiAlH4, respectively. Under 30 bar hydrogen pressure and 300 °C constant temperature, LiAlH4 doped with 7 wt% NiTiO3@h‐BN after dehydrogenation can absorb ≈1.05 wt% hydrogen. Based on density functional theory calculations, AlNi3 and NiTi, in situ formed nanoparticles during ball milling, can decrease the desorption energy barrier of AlH bonding in LiAlH4 and accelerate the breakdown of AlH bonding due to the interfacial charge transfer and the dehybridization. Furthermore, NiTi can enhance the adsorption and splitting of H2, promoting the activation of H2 molecules during the rehydrogenation process.

Exploring yttrium doped C24 fullerene as a high-capacity reversible hydrogen storage material: DFT investigations

By employing the state-of-the-art density functional theory, we report the hydrogen storage capability of yttrium decorated C24 fullerene. Single Y atom attached on C24 fullerene can reversibly adsorb a maximum number of 6 H2 molecules with average adsorption energy − 0.37 eV and average desorption temperature 477 K, suitable for fuel cell applications. The gravimetric weight content of hydrogen is 8.84%, which exceeds the target value of 6.5 wt% H by the department of energy (DoE) of the United States. Y atom is strongly bonded to C24 fullerene with a binding energy of − 3.4 eV due to a charge transfer from Y-4d and Y-5 s orbitals to the C-2p orbitals of C24 fullerene. The interaction of H2 molecules with Y atom is due to the Kubas type interaction involving a charge donation from the metal d orbital to H 1 s orbital, and back donation causing slight elongation of H-H bond length. The stability of the system at the highest desorption temperature is confirmed by ab-initio molecular dynamics simulations, and the metal-metal clustering formation has been investigated by computing the diffusion energy barrier for the movement of Y atoms. We have corrected all the calculated energies for the van der Waals (vdW) interactions by applying the dispersion energy corrections, in addition to the contribution of the GGA exchange-correlation functional. The C24 +Y system is stable at room temperature, and at the highest desorption temperature, the presence of a sufficient diffusion energy barrier prevents metal-metal clustering. Furthermore, binding energies of H2 are within the target value by DoE (−0.2 to 0.7 eV/H2), while H2 uptake (8.84% H) is higher than DoE’s criteria. Therefore, we propose that Y decorated C24 fullerene can be tailored as a practically viable potential hydrogen storage candidate.

Analysis of NH3 -TPD Profiles for CuSSZ-13 SCR Catalyst of Controlled Al Distribution - Complexity Resolved by First Principles Thermodynamics of NH3 Desorption, IR and EPR Insight into Cu Speciation*.

NH3 temperature-programmed desorption (NH3 -TPD) is frequently used for probing the nature of the active sites in CuSSZ-13 zeolite for selective catalytic reduction (SCR) of NOx . Herein, we propose an interpretation of NH3 -TPD results, which takes into account the temperature-induced dynamics of NH3 interaction with the active centers. It is based on a comprehensive DFT/GGA+D and first-principles thermodynamic (FPT) modeling of NH3 adsorption on single Cu2+ , Cu+ , [CuOH]+ centers, dimeric [Cu-O-Cu]2+ , [Cu-O2 2- -Cu]2 species, segregated CuO nanocrystals and Brønsted acid sites (BAS). Theoretical TPD profiles are compared with the experimental data measured for samples of various Si/Al ratios and distribution of Al within the zeolite framework. Copper reduction, its relocation, followed by the intrazeolite olation/oxolation processes, which are concomitant with NH3 desorption, were revealed by electron paramagnetic resonance (EPR) and IR. DFT/FPT results show that the peaks in the desorption profiles cannot be assigned univocally to the particular Cu and BAS centers, since the observed low-, medium- and high-temperature desorption bands have contributions coming from several species, which dynamically change their speciation and redox states during NH3 -TPD experiment. Thus, a rigorous interpretation of the NH3 -TPD profiles of CuSSZ-13 in terms of the strength and concentration of the active centers of a particular type is problematic. Nonetheless, useful connections for molecular interpretation of TPD profiles can be established between the individual component peaks and the corresponding ensembles of the adsorption centers.

Scandium decorated C24 fullerene as high capacity reversible hydrogen storage material: Insights from density functional theory simulations

Using first principles density functional theory simulations, we have observed that the scandium decorated C24 fullerene can adsorb up to six hydrogen molecules with an average adsorption energy of −0.35 eV per H2 and average desorption temperature of 451 K. The gravimetric wt% of hydrogen for the scandium decorated C24 fullerene system is 13.02%, which is sufficiently higher than the Department of Energy, United States demand. Electronic structure, orbital interactions, and charge transfer mechanisms are explained using the density of states, spatial charge density difference plots, and Bader charge analysis. A total amount of 1.44e charge transfer from the 3d and 4s orbitals of scandium to the 2p carbon orbitals of C24 fullerene. Hydrogen molecules are attached to scandium decorated C24 fullerene by Kubas type of interactions. Diffusion energy barrier calculations predict that the existence of a sufficient energy barrier will prevent metal–metal clustering. Ab-initio molecular dynamics (A.I.M.D.) simulations confirm the solidity of structure at the highest desorption temperature. Therefore, we believe that the scandium decorated C24 fullerene system is a thermodynamically stable, promising reversible high-capacity hydrogen storage device.

High-Performance Graphene/Carbon Nanotube-Based Adsorbents for Treating Diluted o-Cresol in Water in a Pilot-Plant Scale Demo.

Graphene/carbon nanotube (CNT)-based adsorbents were fabricated on a kilogram scale by extrusion processing (where graphene is used as the major adsorption material and CNTs make up the backbone to enhance the mechanical strength) and then mixed and bonded with poly(tetrafluoroethylene). Kilogram-scale adsorbents were used to treat the content of o-cresol in wastewater to be <1.12 mg/kg in a continuous and reversible adsorption-desorption apparatus, which could last for 99 h with a space velocity of 30 h-1 and a total wastewater capacity of 5 tons per day. Brunauer-Emmett-Teller (BET), Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), and Raman spectroscopy all suggested that the surface properties and pore structure of the spent adsorbents remain unchanged after recycling at both low-temperature adsorption and high-temperature desorption in vacuum. These results provided an effective reversible adsorbent system for removing aromatic organics and prompted the scaled-up applications of carbon nanomaterials in the treatment of wastewater.

Influence of carbon catalysts on the improvement of hydrogen storage properties in a body-centered cubic solid solution alloy

Body-centered cubic (BCC) alloys are considered as promising materials for hydrogen storage with high theoretical storage capacity (H/M ratio of 2). Nonetheless, they often suffer from sluggish kinetics of hydrogen absorption and high hydrogen desorption temperature. Carbon materials are efficient hydrogenation catalysts, however, their influence on the hydrogen storage properties of BCC alloy has not been comprehensively studied. Therefore, in this paper, composites obtained by milling of carbon catalysts (carbon nanotubes, mesoporous carbon, carbon nanofibers, diamond powder, graphite, fullerene) and BCC alloy (Ti1.5V0.5) were extensively studied in the non-hydrogenated and hydrogenated state. The structure and microstructure of the obtained materials were studied by scanning and transmission electron microscopes, X-ray diffraction (XRD), and Raman spectroscopy. XRD and Raman measurements showed that BCC alloy and carbon structures were in most cases intact after the composite synthesis. The hydrogenation/dehydrogenation studies showed that all of the used carbon catalysts significantly improve the hydrogenation kinetics, reduce the activation energy of the dehydrogenation process and decrease the dehydrogenation temperature (by nearly 100 K). The superior kinetic properties were measured for the composite with 5 wt % of fullerene that absorbs 3.3 wt % of hydrogen within 1 min at room temperature.

Survey Summary on Salts Hydrates and Composites Used in Thermochemical Sorption Heat Storage: A Review

To improve the proficiency of energy systems in addition to increasing the usage of renewable energies, thermal energy storage (TES) is a strategic path. The present literature review reports an overview of the recent advancements in the utilization of salt hydrates (single or binary mixtures) and composites as sorbents for sorption heat storage. Starting by introducing various heat storage systems, the operating concept of the adsorption TES was clarified and contrasted to other technologies. Consequently, a deep examination and crucial problems related to the different types of salt hydrates and adsorbents were performed. Recent advances in the composite materials used in sorption heat storage were also reviewed and compared. A deep discussion related to safety, price, availability, and hydrothermal stability issues is reported. Salt hydrates display high theoretical energy densities, which are promising materials in TES. However, they show a number of drawbacks for use in the basic state including low temperature overhydration and deliquescence (e.g., MgCl2), high temperature degradation, sluggish kinetics leading to a low temperature rise (e.g., MgSO4), corrosiveness and toxicity (e.g., Na2S), and low mass transport due to the material macrostructure. The biggest advantage of adsorption materials is that they are more hydrothermally stable. However, since adsorption is the most common sorption phenomenon, such materials have a lower energy content. Furthermore, when compared to salt hydrates, they have higher prices per mass, which reduces their appeal even further when combined with lower energy densities. Economies of scale and the optimization of manufacturing processes may help cut costs. Among the zeolites, Zeolite 13X is among the most promising. Temperature lifts of 35–45 °C were reached in lab-scale reactors and micro-scale experiments under the device operating settings. Although the key disadvantage is an excessively high desorption temperature, which is problematic to attain using heat sources, for instance, solar thermal collectors. To increase the energy densities and enhance the stability of adsorbents, composite materials have been examined to ameliorate the stability and to achieve suitable energy densities. Based on the reviewed materials, MgSO4 has been identified as the most promising salt; it presents a higher energy density compared to other salts and can be impregnated in a porous matrix to prepare composites in order to overcome the drawbacks connected to its use as pure salt. However, due to pore volume reduction, potential deliquescence and salt leakage from the composite as well as degradation, issues with heat and mass transport can still exist. In addition, to increase the kinetics, stability, and energy density, the use of binary salt deposited in a porous matrix is suitable. Nevertheless, this solution should take into account the deliquescence, safety, and cost of the selected salts. Therefore, binary systems can be the solution to design innovative materials with predetermined sorption properties adapted to particular sorption heat storage cycles. Finally, working condition, desorption temperature, material costs, lifetime, and reparation, among others, are the essential point for commercial competitiveness. High material costs and desorption temperatures, combined with lower energy densities under normal device operating conditions, decrease their market attractiveness. As a result, the introduction of performance metrics within the scientific community and the use of economic features on a material scale are suggested.

Recent Development of Lithium Borohydride‐Based Materials for Hydrogen Storage

Lithium borohydride (LiBH4) has been attracting extensive attention as an exemplary high‐capacity complex hydride for solid‐state hydrogen storage applications because of its high hydrogen capacities (18.5 wt% and 121 kg H2 m−3). However, the strong and highly directional covalent and ionic bonds within LiBH4 structure induce high desorption temperatures, slow kinetics, and poor reversibility, which make large‐scale application impractical. To improve its hydrogen cycling performance, several strategies including cation/anion substitution, catalyst doping, reactive compositing, and nanoengineering, have been developed to tailor the thermodynamics and kinetics of hydrogen storage process. For example, largely reduced operation temperatures and remarkably improved hydrogen storage reversibility under moderate conditions have been achieved by the synergistic effect of nanostructuring and nanocatalysis. Herein, the state‐of‐the‐art development of LiBH4‐based hydrogen storage materials is summarized, including the basic physical and chemical properties, the principles of thermodynamic and kinetic manipulation and the strategies to improve hydrogen storage properties. The remaining challenges and the main directions of future research are also discussed.

Activated carbon adsorbents with micro-mesoporous structure derived from waste biomass by stepwise activation for toluene removal from air

The waste biomass was used as raw materials to prepare activated carbon adsorbents with micro-mesoporous structure. And the prepared activated carbon adsorbents were used to adsorption remove toluene from air, which can achieve the goal of “treat waste with waste”. In this paper, biomass activated carbon adsorbents with micro‒mesoporous structure were prepared by two-stage process of “low temperature carbonization‒high temperature activation” using waste biomass as raw materials and H3PO4 as activator. The obtained results show that the activation temperature can significantly affect the structural characteristics, graphitization degree and surface chemical properties of the prepared adsorbents, and the toluene adsorption and regeneration performances of the adsorbent are significantly affected by its physicochemical properties. High thermal desorption temperature (100 °C) can destroy the strong interaction between the oxygen atoms of the oxygen-containing functional groups on the surface of the adsorbent and the p-electrons of toluene aromatic ring, thus realizing the desorption of corresponding adsorbed toluene molecules. The low heat treatment temperature of 60 °C can destroy the strong adsorption from narrow micropores for toluene and π‒π conjugation effect between the adsorbent and toluene molecules, which can realize the corresponding adsorbed toluene molecules to be desorbed. When the activation temperature is 650 °C, the activated carbon adsorbent with surface area of 1006.2 m2/g, micro-mesoporous structure and mesoporous proportion of 65.5% can be prepared. The adsorption capacity of toluene can reach 417.0 mg/g, and the toluene thermal desorption regeneration can be realized at 60 °C. The results indicate that it is a promising adsorbent material for toluene removal from air

Suitability of Thermal Swing Adsorption for the Treatment of Siloxanes and Toluene in Biogas: An Experimental Study

The use of biogas has been proven to be an interesting alternative energy source. However, biogas usually contains trace compounds, which can lead to damage in the valorization installation. Consequently, their treatment is an important issue for the suitability of biogas valorization. Although thermal swing adsorption (TSA) has already been implemented, there is still a lack of knowledge about the deactivation of the adsorbent. This work examined under dynamic conditions, the treatment of three typical trace compounds from landfills (L2, D4, and toluene) via the TSA process using activated carbon cloth (ACC). The process was implemented according to temperature programs: one with a moderate desorption temperature (180 °C) and the other with a high desorption temperature (220 °C). Both experiments involved several cycles of adsorption and desorption (60 cycles). In the single-compound adsorption experiment, the adsorption capacities were 24%, 19%, and greater than 15% weight basis for toluene, L2, and D4, respectively. From TSA experiments, it was found that the adsorption capacities of the ACC decreased rapidly over the first four cycles for the two temperature programs. This decrease was lower at high temperatures: no significant decrease was found between the 4th cycle and the 50th cycle. On the contrary, a constant decrease was measured at moderate temperatures. Both the surface analysis (infrared measure) and the analysis of the gas from the desorption step indicate that siloxanes were deposited on the ACC and polymerized to a high-molecular-weight polymer. This reaction could cause ACC deactivation by pore clogging. Mass balances and gas analysis also suggested that toluene could be thermally degraded during the desorption step. The high temperatures promoted desorption of high-molecular-weight compounds, such as D5, L5, and D6, formed during adsorption/desorption processes. Thus, a high-temperature program was found to be more effective than a moderate-temperature program.

Nucleation and recombination dependent desorption performance of Mg-based hydrides

High desorption temperature and sluggish desorption kinetics hinder the large-scale application of Mg-based hydrogen storage materials. Fundamental understanding of the dehydrogenation process and underlying mechanism is crucial for further modifying the desorption performance. Aiming at elucidating the dehydrogenation process of Mg-based hydrides, partially desorbed pure MgH2 and MgH2-Mg2NiH4-CeH2.73 composite have been prepared to investigate the effects of metal phase nucleation on overall desorption performance. It is found that metal Mg is formed on the surface of partially desorbed MgH2 and MgH2-Mg2NiH4-CeH2.73. Correspondingly, the desorption temperature of partially desorbed samples is significantly decreased, indicating an important role nucleation plays in desorption process. With minor Ni addition, the desorption temperature and kinetics of MgH2-Mg2NiH4-CeH2.73 are significantly improved. Promoting hydrogen recombination is another essential aspect to modify the desorption properties of Mg hydrides.

CO adsorption on MnO(100): Experimental benchmarks compared to DFT

CO adsorption on the MnO(100) surface was studied using temperature programmed desorption (TPD) and density functional theory (DFT). TPD results show that CO is weakly-bound on MnO(100), with an experimental adsorption energy of -35.6 ± 2.1 kJ/mol at terrace sites in the low coverage limit. PBE simulations suggest that CO adsorption causes an implausible (2 × 2) surface reconstruction. PBE+U simulations show no signs of surface reconstruction, and provide an accurate estimate of the adsorption energy (-36.4 kJ/mol) when combined with the DFT-D3 method with Becke-Jonson damping to correct for van der Waals interactions. This simulation also shows that CO adsorbs C-down onto the Mn2+ terrace site in a tilted geometry, which is also observed experimentally and computationally on the similarly-structured NiO(100) transition metal oxide surface. TPD results for large doses show a plateauing of the coverage at about 0.4 monolayers of CO at 85 K, with a defect coverage equivalent to 0.08 monolayers. Adsorption associated with defect sites is indicated by a high-temperature desorption tail which is not satisfactorily explained by DFT simulations of simple step or oxygen vacancy defects.