Trends In Adsorption Energies Research Articles

Trapping of dichlorosilane (H2SiCl2) gas by transition metals doped fullerene nanostructured materials

Dichlorosilane is a flammable and poisonous gas which is very toxic when inhaled. When handling this gas, extreme precautions must be taken to prevent exposure and so therefore there is need to develop a more sensitive and affordable sensor to detect and measure the concentration of gas in the environment in case of unintentional release of the gas into the air. Overtime, structured materials have been used in the adsorption of target gas. Herein, the detection of dichlorosilane (H2SiCl2) gas by transition metals (X = Cr, Fe, Ni, Ti, and Zn) anchored fullerene is studied using the density functional theory (DFT) computation at theωB97X-D/gen/6-311++G(d,p)/LanL2DZ level of theory. From the electronic properties, large energy gap signifies lower electrical conductivity and sensitivity. The result showed an increase in the energy gap on adsorption of the gas on nanocages except for N1 and T1 where the energy gap was lesser than that of the nanocages. Calculations shows among the five studied surfaces, C23–Ti surface emerged with the highest adsorption energy value of −2.231 eV and corresponding energy gap value of 5.200 eV. Also, the decreasing trend of adsorption energies: H2Cl2SiC23Ti (T1), (−2.231) > H2SiCl2C23Ni (N1), (−2.095) > H2SiCl2C23Zn (Z1) (−2.068) > H2SiCl2C23Cr (C1) (−1.796) > H2SiCl2C23Fe (F1) (−1.742) was observed. High negative value of adsorption energy, the lesser the recovery time. H2Cl2SiC23Ti (T1) complex with high negative value of adsorption energy has a lesser recovery time exhibits better sensing attributes. The C23–Ti surface is relatively a better candidate in the adsorption and, hence, confirmed as suitable nanosensor material for the detection and adsorption of toxic dichlorosilane (H2SiCl2) gas molecule.

A structure-sensitive descriptor for the design of active sites on MoS2 catalysts

cn, a metric based on the number of sulfur atoms coordinated to Mo atoms, captures the trends in adsorption energies and activation energies of various species on MoS2(001) catalysts with sulfur vacancies.

Insights into glyphosate adsorption on Lewis acidic zeolites from theoretical modelling

The removal of glyphosate via the adsorption process is one of the essential routes for decreasing its harmful impact. Here, we investigate the glyphosate adsorption on the Lewis acidic zeolites through density functional theory (DFT) calculations. We found that Hf-BEA provides the highest adsorption energy (−44.1 kcal/mol) as compared to ones of other zeolites. This result corresponds to its highest ordered Lewis acidity calculated by ammonia adsorption. There is a strong correlation between glyphosate and ammonia adsorption energies, as shown in a linear scaling relationship. This result implies the significant role of the Lewis acidity strength of zeolite in glyphosate adsorption process. The adsorption activity which related to zeolite pore structures (BEA, FAU, ZSM-5 and MOR) are found in the order of Hf-BEA > Hf-ZSM-5 ∼ Hf-MOR > Hf-FAU. The effect of water on the glyphosate adsorption is also investigated. Water is adsorbed on Sn-BEA zeolite much weaker than glyphosate and thus the active site of zeolite cannot be blocked by it. The trend of adsorption energies remains the same as in vacuum. Finally, the hydrolysis of metal-substituted active sites to form open sites strengthens the adsorption of glyphosate.

Adsorption of Cr (III) and Cr (VI) ions on muscovite mica: Experimental and molecular modeling studies

The article explores the possibility of adsorption of Cr (III) and Cr (VI) ions on muscovite mica for the first time. The adsorption behaviors of both the ions on the mineral have been compared vide experimental and molecular modeling studies. Experiments have been carried out to find out the effects of different operating parameters on the adsorption of the metal ions, while Density Functional Theory (DFT) based simulations have been conducted to understand the adsorption mechanisms of various Cr (III) and Cr (VI) species, occurring at different pH, on muscovite (001) surface. The maximum metal removal efficiencies obtained for Cr (III) and Cr (VI) are about 15.6 mg/g and 1.74 mg/g, respectively. The trend of adsorption energies calculated using DFT supports this finding. The simulation studies depict the nature of bonding of various possible Cr ions, at different pH levels, on the muscovite surface and reveal that the patterns Cr-O bonds and hydrogen bonds define the adsorption mechanism. The Partial Density of States (PDOS) calculations provide a further understanding of the involvement of different orbitals of Cr, O, H of the Cr ion and O atom of muscovite surface in the metal-mineral interaction.

Thermodynamics and Kinetics of Molecular Hydrogen Adsorption and Dissociation on MXenes: Relevance to Heterogeneously Catalyzed Hydrogenation Reactions

The interaction of molecular hydrogen with a series of 28 two-dimensional (2D) carbides and nitrides, known as MXenes, has been studied by means of periodic density functional calculations. This study shows that trends in atomic and molecular adsorption energies can be rationalized in terms of the electrostatic potential above the surface site and the Bader charge on the surface metal atoms. For all systems, molecular hydrogen is found to dissociate with almost negligible barriers, meaning that at low temperature the MXene surface will be passivated by adsorbed atomic hydrogen. The conditions at which the MXene surface is partly covered and, hence, able to participate in hydrogenation reactions are investigated by means of ab initio thermodynamics and phase diagrams derived from microkinetic simulations. The first provide the equilibrium conditions for a given H coverage on the MXene of interest, whereas the second provides the conditions at which a given configuration is reachable at the working conditions. For fast enough processes, both approaches necessarily lead to the same result, but this may differ when high energy barriers are involved, as it the case here for the H adatoms recombination step. With this suite, we show that Fe2C, W2N, and Mo2C are promising hydrogenation catalysts. This work serves as a first step toward the rational design and implementation of MXene-based hydrogenation catalysts.

Sensing capability and diameter-dependent electronic structure of boron nitride nanotubes

The sensing and diameter-dependent properties of armchair Boron Nitride nanotubes (BNNTs) were scrutinized based on density functional theory (DFT) to find out their electronic structure and carbon monoxide (CO) sensing capability. Our results show that diameter increase causes a rise in the binding energy of BNNT, from 6.44 eV to 6.62 eV. An increasing trend of adsorption energies in the range of -3.25 and -3.47 kcal/mol indicates that BNNTs act weak physical adsorption upon CO verified by the analysis of the Electron localization function (ELF), however, more increase in the diameter could enhance the sensing capability of BNNT. The energy gap of the biggest BNNT is calculated as 6.20 eV wide, i.e., about 0.12 eV smaller than the smallest one which is compatible with available experimental results. The reactivity properties such as the adiabatic and vertical ionization potentials (IPs), chemical hardness, and electrophilicity index of BNNTs were also analyzed. The BNNTs exhibit strong absorption peaks ∼7.08 eV which can be a promising candidate for the UV light-emitting devices. The results herein reveal that BNNTs with bigger diameters can be useful for gas sensor applications.

Perspective on experimental evaluation of adsorption energies at solid/liquid interfaces

Almost 15 years ago, first papers appeared, in which the density functional theory (DFT) was used to predict activity trends of electrocatalytic reactions. That was a major contribution of computational chemistry in building the theory of electrocatalysis. The possibility of computational electrocatalyst design had a massive impact on the way of thinking in modern electrocatalysis. At the same time, substantial criticism towards popular DFT models was developed during the years, due to the oversimplified view on electrified interfaces. Having this in mind, this work proposes an experimental methodology for quantitative description of adsorption energies at solid/liquid interfaces based on the Kelvin probe technique. The introduced approach already gives valuable trends in adsorption energies while in the future should evolve into an additional source of robust values that could complement existing DFT results. The pillars of the new methodology are established and verified experimentally with very promising initial results.

Influence of Acidity on the Methanol-to-DME Reaction in Zeotypes: A First Principles-Based Microkinetic Study

Acidity is considered a key factor in zeotype-based catalysts. Here, the effect of acidity in the methanol-to-DME reaction is investigated using first-principles calculations and microkinetic modeling, thereby establishing a connection between acididity and kinetics. The CHA, MFI, and BEA frameworks are investigated, and the acidity of the Brønsted hydroxyl group is varied by exchanging a T-site Si with Al, B, Ga, and Fe in the zeolites, along with SAPO-34, Mg-AlPO-34, Zn-AlPO-34, and Ti-AlPO-34 zeotypes with the CHA structure, and as a result, the Brønsted hydroxyl group spans a wide range of acidity. Clear trends in adsorption and transition-state energies are found and by means of linear regression, we obtain scaling relations of relevant energies that are later used as input in a mean-field steady-state microkinetic model. This study confirms that both the shift in frequency of the Brønsted hydroxyl stretch, ΔfOH, caused by adsorption of CO and the ammonia adsorption energy, ΔEammonia, on the Brønsted site are equivalent descriptors for the acidity of the Brønsted acid site and the reactivity of the different zeotypes relevant for the methanol-to-DME reaction. It further shows that a full microkinetic model is needed to accurately describe the reaction over the whole range of temperatures. However, if focusing on low temperatures, where the associative mechanism is dominating the reaction, a simple rate-determining step model is actually able to describe the results with satisfying agreement (deviation of the rate by less than a factor of two).

Tailoring of graphene quantum dots for toxic heavy metals detection

The sensitivity of graphene quantum dots towards toxic heavy metals (THMs; Cd, Hg, Pb) can be improved through doping with nitrogen at the vacant site defects. Using density functional theory, we investigate the adsorption of THMs on the graphene quantum dots (GQDs) and nitrogen-coordinated defective GQDs (GQD@1N, GQD@2N, GQD@3N and GQD@4N) surfaces. Thermochemistry calculations reveal that the adsorption of Pb atom on the surfaces is more favorable than Cd and Hg adsorption. The decoration of the vacant defects with nitrogen on the GQD surface substantially increases the charge transfer and adsorption energy values of THMs on the GQD surface (GQD@4N > GQD@3N > GQD@1N > GQD@2N > GQD). The charge transfer and adsorption energy of lead on each of these surfaces are greater than those of cadmium and mercury (Pb > Cd > Hg). Quantum theory of atoms in molecules analysis and non-covalent interaction plots further validate this result while also confirming that Pb atom has a partially covalent and electrostatic nature of interaction at the nitrogen-coordinated vacant site defects. The electron density values—a criterion of bond strength—for the THM...N interactions are greater than for the THM…C interactions, confirming the observed adsorption energy trends of the THMs on the surfaces. The lowering of the HOMO–LUMO energy gap of the surfaces follows the order Pb > Cd > Hg and also results in increased electrical conductivity, which are consistent with the calculated adsorption energy trends. Significant changes in the energy gap and electric conductivity of the surfaces upon THMs adsorption make them promising sensors for metal detection. Finally, time-dependent density functional theory calculations showed that changes such as peak shifts, peak quenching and appearance of new peaks are seen in the UV–visible absorption spectra of the surfaces upon adsorption of THMs, wherein the shifts in peaks correspond to the magnitude of adsorption energy of THMs on the surfaces. These results should motivate the experimentalists towards using rational and systematic modulation of surfaces as sensors for heavy metal detection.

Transition‐Metal‐Based Multidecker Complexes as Hydrogen Storage Materials: A Theoretical Study

AbstractHydrogen economy has gained pace globally due to the depletion of fossil fuels at an alarming rate. A good number of multidecker transition metal complexes have been studied for their hydrogen storage ability. However, the problem of finding an ideal multidecker system for hydrogen storage applications still remains a challenge. Herein, we report a comparative study on multidecker complexes of VTi(C6H6)3, Sc2(C6H6)3, and Sc2(C5H5)2(C6H6) using density functional theory at PBEPBE functional and 6–31G (d,p) basis set level of theory. The three complexes show hydrogen adsorption capacity in a range of 2.94 to 5.28 wt%, with an average binding energy of 0.65 to 0.92 eV/H2. Trends in adsorption energies, Gibbs free energy changes and energy gaps indicate the adsorption of H2 molecules on these multidecker complexes is thermodynamically and kinetically favorable.

Controlling the surface chemistry towards unsaturated carbon-carbon bonds over non-oxide transition metal ceramics: Trends in adsorption and distortion energies and adsorbate “activation”

Controlling the surface chemistry of catalysts towards unsaturated carbon-carbon bonds is vital to achieving many contemporary chemical transformations. Transition metal (TM) ceramics are promising materials that exhibit lower and tunable surface reactivity towards C=C bonds. Herein, we have employed an analysis of the adsorption of benzene over a large suite of TM ceramic and pure metal surfaces to benchmark a large selection of materials to isolate trends. Results showed a wide range of surface reactivity as a function of the constituent elements, surface composition, TM-to-p-element ratio, surface ensemble size, electronic structure, etc. The 1st row TM ceramics exhibited lower surface reactivity and more stable surface composition than the 2nd/3rd TM ceramics suggesting that orbital-size match could be a simple marker for predicting general surface chemistry and surface composition stability in TM solid compounds. The TM-to-p-element ratio also generally dictated metal-like or markedly-modified reactivity of the constituent elements at the ceramic surface. Electronic analysis further quantified the correlation between the density and type of electronic states near the Fermi level and the reactivity of surface-lattice elements. Structural and energetic analysis of the adsorbed benzene indicated the activation of the adsorbate could be better quantified beyond simple adsorption energy.

Oxidation of Ethylene Carbonate on Li Metal Oxide Surfaces

Understanding the reactivity of the cathode surface is of key importance to the development of batteries. Here, density functional theory is applied to investigate the oxidative decomposition of the electrolyte component, ethylene carbonate (EC), on layered LixMO2 oxide surfaces. We compare adsorption energy trends of atoms and small molecules, on both surface oxygen and metal sites, as a function of the Li content of the surface. The oxygen sites are identified as the reactive site for the electrolyte oxidation reaction (EOR). We report reaction energies and NEB-calculated kinetic barriers for the initial oxidative decomposition of EC, and correlate both with the reaction energy of hydrogen adsorption on oxygen. The hydrogen adsorption energy scales with the distance between the Fermi level and the O-2p band center. We expect this model of the EOR to be valid for other organic electrolytes and other Li metal oxide surfaces, due to its simplicity, and the model leads to simple design principles for protec...

Comparison of the Performance of van der Waals Dispersion Functionals in the Description of Water and Ethanol on Transition Metal Surfaces

Pairwise van der Waals (vdW) corrections have been routinely added to density functional theory (DFT) adsorption studies of inorganic or organic molecules on solid surfaces, however, comparative studies of the available pairwise corrections, e.g., D2, D3, D3(BJ), TS, and TS+SCS, are quite scarce. We report DFT calculations within the Perdew–Burke–Ernzerhof (PBE) functional to assess the performance of the mentioned pairwise vdW corrections for well-defined transition-metal (TM) systems, namely, the Cu, Pt, and Au bulks in the face-centered cubic structure, close-packed TM substrates (Cu(111), Pt(111), Au(111), Cu9/Pt9/Cu(111), Pt9/Cu9/Cu(111), Au9/Pt9/Au(111), Pt9/Au9/Au(111)), and the adsorption of water and ethanol on the selected substrates, which include strained Pt-monolayers, i.e., a good challenge for pairwise vdW corrections. In general, accounting for vdW interactions leads to smaller lattice constants, which is expected due to the attractive nature of the vdW corrections, and the D3, D3(BJ), and TS+SCS improves the DFT-PBE results, in contrast with D2 and TS. Compared with PBE results, the vdW corrections enhance the contraction of the topmost surface layers, which contributes to change the electronic structure, in particular, the d-band center shifts away from the Fermi energy (up to 0.3 eV) in most cases, while the work function changes by about 0.2 eV in the worst cases. As expected, the attractive nature of the vdW corrections helps to enhance adsorption energies by 3–4 times compared with DFT-PBE. However, the adsorption energy trends versus the d-band center are preserved for all vdW corrections, except for the DFT-D2 framework, which deviates substantially from the studied vdW corrections. Therefore, based on our results and analyses, we can conclude that the D3, D3(BJ), and TS+SCS corrections yield the best description for the selected systems.

Systematic Study of Aluminum Nanoclusters and Anion Adsorbates.

The interactions between aqueous aluminum (Al) nanoclusters and ions in solution influence the reactivity of nanomaterials in natural waters and are crucial to the targeted syntheses of aluminum oxides. To contribute to the fundamental understanding of how both anion and Al-nanocluster properties affect the interactions, we carry out systematic modeling studies that employ density functional theory calculations embedded in a continuum solvent model. Energetic and electronic structure analysis is applied toward delineating the interactions of a range of probe adsorbate anions with Al nanoclusters to elucidate how small molecules may react with naturally occurring nanomaterials. The study spans seven small molecules on three model Al nanoclusters. Using this ion set, we correlate the size, shape, and formal charge of the adsorbate to the trends in adsorption energies. A key finding is that the collective effects of exposed oxygen functional groups, i.e., the distribution of functional groups, dictates the electrostatic potential of the nanocluster surface, which, in turn, controls trends in anion adsorption. The computed adsorption and deprotonation trends are correlated to known synthetic routes of Al-nanocluster formation and subsequent crystallization to give insight into the potential optimization of synthetic conditions.

Trends in Adsorption Energies of the Oxygenated Species on Single Platinum Atom Embedded in Carbon Nanotubes

Herein we study the effect of strain on the catalytic activity of different Pt-doped single wall metallic carbon nanotubes (SWCNT) towards the oxygen reduction reaction (ORR). We consider the possibility of the Pt-doped at single vacancy inside the SWCNT to investigate the effect of confinement on the reaction mechanism. Density functional theory calculations indicate that for the SWCNTs with tube diameters below 7 A, the strain energy varies significantly influencing the adsorption energies of the key intermediates of the ORR reaction. For the SWCNTs with tube diameters above 7 A, on the other hand, both the calculated strain and the adsorption energies are almost constant. We furthermore find that the adsorption energies are strongly affected by confinement effects as shown for Pt-doped systems that are located inside the SWCNT. We show that the Pt-doped at single vacancy of the SWCNT strongly binds the oxygenated species under ORR potentials and therefore the active species is covered by oxo- or hydroxo group. Because the presence of Pt atoms doped at the single and double vacancies of the SWCNT is equivalently probable we also studied the Pt-doped at double vacancy. We find that the most active motif is the Pt-doped at double vacancy of SWCNT with 0.24V overpotenital.

Theoretical evaluation on selective adsorption characteristics of alkali metal-based sorbents for gaseous oxidized mercury

Alkali metal-based sorbents are potential for oxidized mercury (Hg2+) selective adsorption but show hardly effect to elemental mercury (Hg0) in flue gas. Density functional theory (DFT) was employed to investigate the Hg0 and HgCl2 adsorption mechanism over alkali metal-based sorbents, including calcium oxide (CaO), magnesium oxide (MgO), potassium chloride (KCl) and sodium chloride (NaCl). Hg0 was found to weakly interact with CaO (001), MgO (001), KCl (001) and NaCl (001) surfaces while HgCl2 was effectively adsorbed on top-O and top-Cl sites. Charge transfer and bond population were calculated to discuss the covalency and ionicity of HgCl2 bonding with the adsorption sites. The partial density of states (PDOS) analysis manifests that HgCl2 strongly interacts with surface sites through the orbital hybridizations between Hg and top O or Cl. Frontier molecular orbital (FMO) energy and Mulliken electronegativity are introduced as the quantitative criteria to evaluate the reactivity of mercury species and alkali metal-based sorbents. HgCl2 is identified as a Lewis acid and more reactive than Hg0. The Lewis basicity of the four alkali metal-based sorbents is predicted as the increasing order: NaCl < MgO < KCl < CaO, in consistence with the trend of HgCl2 adsorption energies.

Adsorption of CO on Low-Energy, Low-Symmetry Pt Nanoparticles: Energy Decomposition Analysis and Prediction via Machine-Learning Models

We present a systematic analysis of CO adsorption on Pt nanoclusters in the 0.2–1.5 nm size range with the aim of unraveling size-dependent trends and developing predictive models for site-specific adsorption behavior. Using an empirical-potential-based genetic algorithm and density functional theory (DFT) modeling, we show that there exists a size window (40–70 atoms) over which Pt nanoclusters bind CO weakly, the binding energies being comparable to those on (111) or (100) facets. The size-dependent adsorption energy trends are, however, distinctly nonmonotonic and are not readily captured using traditional descriptors such as d-band energies or (generalized) coordination numbers of the Pt binding sites. Instead, by applying machine-learning algorithms, we show that multiple descriptors, broadly categorized as structural and electronic descriptors, are essential for qualitatively capturing the CO adsorption trends. Nevertheless, attaining quantitative accuracy requires further refinement, and we propose...

Water activation and carbon monoxide coverage effects on maximum rates for low temperature water-gas shift catalysis

Linear scaling relations and Brønsted-Evans-Polanyi (BEP) relations help to elucidate trends in activation energies and adsorption energies on different metal surfaces. In this paper, Density Functional Theory (DFT) calculations available in the literature are utilized to analyze these trends and their effect on the reactivity of transition metals for the low temperature water-gas shift reaction (CO+H2O↔CO2+H2). The importance of OCO bond formation in water-gas shift is shown for metals not limited by water dissociation. In addition, the CO binding energy is shown to be an important parameter, as CO can crowd out the free sites which participate in adsorption steps, water dissociation, and carboxyl decomposition. From these results, we propose a catalyst design strategy to combine metals that adsorb O weakly, such as Au clusters or Pt nanoparticles, with supports that exhibit strong enough interactions with oxygen to be capable of easily dissociating water.

Two-Dimensional Materials as Catalysts for Energy Conversion

Although large efforts have been dedicated to studying two-dimensional materials for catalysis, a rationalization of the associated trends in their intrinsic activity has so far been elusive. In the present work we employ density functional theory to examine a variety of two-dimensional materials, including, carbon based materials, hexagonal boron nitride (h-BN), transition metal dichalcogenides (e.g. MoS2, MoSe2) and layered oxides, to give an overview of the trends in adsorption energies. By examining key reaction intermediates relevant to the oxygen reduction, and oxygen evolution reactions we find that binding energies largely follow the linear scaling relationships observed for pure metals. This observation is very important as it suggests that the same simplifying assumptions made to correlate descriptors with reaction rates in transition metal catalysts are also valid for the studied two-dimensional materials. By means of these scaling relations, for each reaction we also identify several promising candidates that are predicted to exhibit a comparable activity to the state-of-the-art catalysts. Scaling relationship for the chemisorption energies of OH* and OOH* on various 2D materials.

Surface chemistry of oxygen on aluminum--Performance of the density functionals: PBE, PBE0, M06, and M06-L.

We investigated the performance of the density functional theory (DFT) functionals PBE, PBE0, M06, and M06-L for describing the molecular and dissociative adsorption of O2 onto pure and doped Al(111) surfaces. Adsorption of O2 was studied at the perfect Al(111) surface and compared with the case where an additional Al atom was present as an adatom. Additionally, we studied how these functionals perform when different dopants are present at the Al(111) surface in two distinct geometries: as an adatom or as a substitutional atom replacing an Al atom. The performance of the different functionals is greatly affected by the surface geometry. The inclusion of Hartree-Fock exchange in the functional leads to slight differences in adsorption energies for molecular adsorption of O2 . These differences become very pronounced for dissociative adsorption, with the hybrids PBE0 and M06 predicting more exergonic adsorption than PBE and M06-L. Furthermore, PBE0 and M06 predicted trends in adsorption energies for defective and perfect surfaces which are in line with the experimental knowledge of the effects of surface defects in adsorption energies. The predictions of the non-hybrids PBE and M06-L point in the opposite direction. The analysis of the contributions of the van der Waals (vdW) forces to the adsorption energies reveals that the PBE and PBE0 functionals have similar difficulties in describing vdW interactions for molecular adsorption of O2 while the M06 functional can give a description of these forces with an accuracy which is at least similar to that of the correction of the D3 type.