Adsorption Energy Levels Research Articles

Al-doped Li4SiO4 for cyclic solar energy storage and CO2 capture: An experimental and DFT study

The substantial consumption of fossil fuels gives rise to excessive carbon dioxide emissions, and mitigating them has emerged as a pressing global priority. The use of renewable energy and carbon capture, utilization, and storage are recognized as two major approaches for carbon neutrality. Li4SiO4 materials exhibit promising prospects in both thermochemical heat storage for solar energy power and cyclic high-temperature CO2 capture. The reactivity between Li4SiO4 and CO2 plays the vital role in its energy storage and CO2 capture performance. Herein, we prepare Al-doped Li4SiO4 materials through an impregnated suspension technique, simultaneously achieving high contact areas and lattice defects to enhance both fast chemisorption and ion diffusion processes. The results show that Al-doped Li4SiO4 exhibits high average energy density of 56677.08 kJ/kmol within 30 cycles. Additionally, the granulated Al-doped Li4SiO4-based pellets, produced via the freeze-drying technique, exhibit negligible energy density loss rate of less than 9 % and acceptable mechanical strength. Furthermore, the CO2 sorption performance also reaches a high value of 0.27 g/g. The reaction mechanism between Li4SiO4 and CO2 has been investigated at both macroscopic and microscopic levels through kinetic analysis and DFT calculations. The simulated Al-doped Li4SiO4/CO2 sorption system possesses increased adsorption energy level from −0.81 eV for the undoped one to −0.95 eV, thereby leading to the improved CO2 sorption. In general, Al-doped Li4SiO4 materials demonstrate great potential for applications in thermochemical heat storage and CO2 capture.

Enhanced product quality through hydrodesulfurization of pyrolysis gasoline over a mixed metal oxide catalyst: An experimental and DFT study

Manipulating electronic properties of the hydrodesulfurization (HDS) catalysts can greatly impact the resulting product distribution. To address such effect decently in theoretical and experimental approaches, high-performance cobalt-molybdenum-supported alumina-titania (CoMo/Al2O3-TiO2) with different TiO2 loadings of 10–28 wt% were synthesized. The characterization of the catalysts was implemented by FE-SEM, TEM, XRD, BET/BJH (based on N2 adsorption–desorption), Fourier transform infrared spectroscopy (FTIR), H2-Temperature programmed reduction (H2-TPR), NH3-Temperature programmed desorption (NH3-TPD), and Thermal gravimetric analysis (TGA). The synthesized catalysts were evaluated through HDS of an industrial feedstock– pyrolysis gasoline (Pygas) in a pilot plant tubular fixed bed reactor. It was found that the modification of the electronic properties by titania could also increase the surface acidity while improving the reductive behavior of the tetrahedral and octahedral molybdenum species. In addition, the CoMo/Al2O3-TiO2 with 10 wt% titania content could excellently remove over 96% of sulfur-containing molecules in Pygas. Besides, the developed CoMo catalyst showed an increase in the aromatic compounds, resulting in improved product quality and value through the HDS process. Furthermore, the contribution of TiO2 to the synthesized catalyst was theoretically interpreted through the density functional theory (DFT) method. It was found that lower adsorption energy levels were estimated for the adsorption of the sulfur-bearing molecules on the CoMo/Al2O3-TiO2 than the CoMo/Al2O3 catalyst.

Plasmon-enhanced Hydrogen evolution reaction kinetics through the strong coupling of Au-O Bond on Au-MoO2 heterostructure nanosheets

How do the synergistic effects work and which dominate the distribution of active sites, that's an interesting question in mang plasmon-enhanced catalysis. Herein, we put a deep insight into the distribution of active sites and the mechanism of charge transfer at the noble metal-metal oxide interface for accelerating the hydrogen evolution reaction (HER) kinetics. A heterostructure of Au loaded MoO 2 nanosheets (Au-MoO 2 ) is prepared by the light-reduction method. EXAFS analysis demonstrates the tight coupling at Au-MoO 2 interface through the Au-O bond. An enhanced HER activity is observed with an overpotential decrease of (Δη) 176 mV and Tafel slop down to 52.5 mV/dec. KPFM measurement and FEM simulation verify the high local field enhancement at the junction. This field induces the concentrated surface charge through the Au-O bond. DFT calculation confirms the upraises filling of Op orbital in the Au-O bond, thus degrading the hydrogen adsorption energy level for HER kinetics. • A strong coupling heterostructure of Au-MoO 2 nanosheets was constructed through a photoassisted deposition. • EXAFS analysis demonstrates the tight coupling at the Au-MoO 2 interface through the Au-O bond. • The high plasmonic field induces the concentrated surface charge through the Au-O bond. • The upraises filling with O 2p orbital in the Au-O bond will degrade the hydrogen adsorption energy level.

Effective degradation of sulfur mustard simulant using novel sulfur-doped mesoporous zinc oxide under ambient conditions

Sulfur doped metal oxides were synthesized using a two-step precipitation method. When reacted against neat 2-CEES (2-chloroethyl-ethyl sulfide, a mustard gas simulant) under ambient conditions, sulfur doped mesoporous zinc oxide (MS-Zn) showed higher catalytic activity than the other metal oxides with 92.7% overall conversion in 24 h for a 2.5 μL neat 2-CEES droplet added on top of 2 × 2 cm large 400 mg catalyst layer. The reaction proceeded mainly by hydrolysis and further solvolysis reaction also occurred depending on the extracting solvents. Cyclic sulfonium ion intermediate reaction was thought to be involved in this reaction, and metal oxide surfaces were thought to facilitate the formation of sulfonium ions from adsorbed 2-CEES. All other by-products were also found to form via sulfonium ions, reconfirming the well-known importance of this intermediate species for the degradation reaction to proceed. The sulfur content for MS-Zn was varied and tested for degradation of neat 2-CEES. This modification showed that there is an optimal amount of sulfur content for the peak catalytic activity of MS-Zn for 2-CEES degradation. Adsorption energy of a 2-CEES molecule was calculated on model sulfur doped and non doped zinc oxide surfaces and the different adsorption energy levels were correlated with the catalytic activity of sulfur doped zinc oxide.

Co-doped graphene sheets as a novel adsorbent for hydrogen storage: DFT and DFT-D3 correction dispersion study

In this study, transition metals (TM) such as palladium (Pd) have been introduced on co-doped graphene and defect graphene sheets with nitrogen and boron ad-atoms to investigate the potentials of new adsorbents for hydrogen storage. The first principle studies using density functional theory (DFT) and DFT-D3 correction dispersion were undertaken to calculate the adsorption energy of hydrogen molecule on the graphene sheet. The results showed that applying Pd transition metal could enhance adsorption energy of hydrogen molecules towards pristine sheet. The main problem in applying transition metal on graphene sheets was concerned with clustering. However, the current defects in graphene sheets prevent clustering event. Our simulation results suggested that these defects reduced hydrogen adsorption and substitute dopants such as nitrogen and boron together on graphene sheets could improve the adsorption energy. Thus, two various forms of Pd decorated NB co-doped as hexagonal and double carbon vacancy (DCV) were introduced as new structures for hydrogen storage. A physical adsorption, which is appropriate for reversible hydrogen storage, was implemented for both novel adsorbents. In the two various forms of NB co-doped structures, DCV had the optimum adsorption behavior as adsorption energy level and density of state (DOS) phenomena. Moreover, the results of adsorption energy using DFT method were consistent with that of DFT-D3 correction dispersion and higher amounts of adsorption energy in DFT-D3 method were obtained. Finally, results introduced Pd decorated NB co-doped graphene sheets as a novel material for hydrogen storage.

NMR Study of HD Adsorbed in a Z-type Metal-Organic Framework

We report the results of measurements of the nuclear spin-lattice and spin-spin relaxation rates of hydrogen deuteride trapped in the mesoporous cages of a metal organic framework (MOF) for temperatures 2.2 < T < 50 K There is considerable interest in the use of this class of materials for hydrogen storage because of the high density of adsorption. NMR studies can provide important information about the molecular interactions and dynamics inside the cages of the MOF structure. Samples were studied with filling factors of 0.1 and 1.0 molecules per cage as determined by the adsorption isotherm at 77 K The results show strong peaks in the relaxation times at several well defined temperatures that are very different from the adsorption energy levels. The origin of these peaks is discussed in terms of the quantization of the translational degrees of freedom of the molecules inside the cages and the associated discrete energy levels. Measurements of the nuclear spin-spin relaxation times also provide an important measure of the diffusivity of hydrogen through the MOF structure which is a critical parameter for the use of MOFs for storage and transport.

Effective interactions in multisite cells for adsorption in microporous materials

Local, discrete models of self-interacting multisite adsorption cells have been shown to be able to provide a coarse-grained representation of equilibrium properties of small molecules adsorbed in nanoporous materials at the mesoscopic scale. In the present work we show how the essential statistical properties of a host cell of structured sites with multiple adsorption energies and particle-particle interactions (that is the partition function, the average energy, and the average number of guests close to the windows connecting the cell to its surroundings) can be reproduced by a less-structured cell with two occupancy-dependent adsorption energy levels.

Indium Nanowire Growth on Si (001) Surface Using Density Functional Theory

Density functional theory was utilized to investigate the growth of an indium nanowire on a Si (001) buckled surface. A site between the edge of two Si dimers is most favorable when the first In atom is adsorbed on the surface at an adsorption energy level of 2.26 eV. The energy barriers for migration from other sites to the most favorable site are low. When the second In atom is adsorbed next to the first In atom to form an In dimer perpendicular to the Si dimer row, the adsorption energy is the highest among all adsorption sites. The third In atom prefers either of the sites next to the In dimer along the In dimer direction. The fourth In atom exhibited the same tendency showed by the second atom. The second and fourth In adsorption energy levels are higher than the first and third levels as the In atoms consume the third valence electron by forming In dimers. Therefore, the In nanowire grows perpendicular to the Si dimer row on the Si (001) surface, as it satisfies the bonding of the three valence electrons of the In atoms.

Laser-induced quantum adsorption of neutral atoms in dielectric surfaces

We propose an optical technique to load neutral atoms in quantum adsorption states of a dielectric surface. Considering a realistic atom–surface potential well, we show that free cold lithium atoms approaching a LiF surface may be transferred to a surface bound state of the first excited atomic state. We also discuss schemes to populate adsorption energy levels of the atomic electronic ground state, and we find that spontaneous mechanisms transfer more than 90% of the excited adsorbed atoms into vibrational levels of the fundamental adsorption potential. The lifetime of the resulting two-dimensional waveguide is calculated, considering the adatoms’ interaction with the crystal phonons.

The Fermi–Dirac concept for isotherms of adsorbents with heterogeneous surfaces

The integral equation for isotherms is reviewed in order to select simple, practical, high-performance energy distributions from among the numerous existing models. Adsorption equilibria can be derived from occupation indices of suitable distributed energy levels. For mono sites, the occupation index is a Fermi–Dirac function. Whether a surface is energetically heterogeneous or homogeneous depends on the ratio of the breadth of the energy level distribution σ to the thermal fluctuation kT . Although, there are only a few energy distributions for which analytic isotherm equations are known, the numerical evaluation shows general properties: the symmetry point Θ = 1 2 , the temperature domain for real or ideal behaviour and isotherm shapes without extrema. As an example, experimental equilibria of CO at molecular sieve 5A are fitted to a hyperbolic energy distribution using four physical parameters: the reference loading, a reference fluid phase pressure φ ( Θ = 1 2 , T ref ) , the mean value and the standard deviation of the adsorption energy level distribution.

Industrial surfaces behaviour related to the adsorption and desorption of hydrogen at cryogenic temperature

The determination of the hydrogen adsorption capacity on different industrial surfaces has been carried out by measuring isothermal adsorption. First results show that the adsorption capacity is mainly determined by surface porosity. Therefore, the samples may be classified into two categories: smooth and porous surfaces. Thermal desorption spectra reveal two adsorption energy levels for hydrogen physisorbed on porous materials, but only a single one on smooth samples. The value of the lowest energy level seems to be independent of the substrate nature. The physisorption process studied at low coverage, well below a monolayer, shows that these two levels are not well defined but an energy distribution exists for each of them. The influences of the isotherm temperature and an annealing at 7 K of an adsorbed monolayer on hydrogen adsorption capacity have been studied.

Evaluation of the Distribution Function of Adsorption Site Energies Based on the Fermi–Dirac's Law in a Monolayer

A model is proposed for physical adsorption of gases on homogeneous solid surfaces on the basis of the Fermi–Dirac's distribution function. The carbon fibers before and after anodic surface treatment are employed in this study conducted by the technique of inverse gas chromatography (IGC) at finite dilution. This distribution function leads to the probability of a given state of site energy and then the potential of the molecules (or the adsorption energy level), determining their tendency to move at a gas sold interface. When evaluating the distribution function with the amount adsorbed, we propose, for the starting adsorption value, a method using values measured by IGC at infinite dilution, instead of Hobson's or Adamson's method. It is found that the adsorption energy level measured withn-hexane and ethyl acetate on carbon fibers is increased by the anodic surface treatment. In particular, the results given by ethyl acetate, which is able to display the polar force on the carbon fibers treated, showed a significant increase when compared to nonpolar probes (n-hexane). This is probably due to the effect of surface chemical polar groups on adsorption energetics.