Combination Of DFT Calculations Research Articles

High‐Performance K–CO2 Batteries Based on Metal‐Free Carbon Electrocatalysts

AbstractMetal–CO2 batteries have attracted much attention owing to their high energy density and use of greenhouse CO2 waste as the energy source. However, the increasing cost of lithium and the low discharge potential of Na–CO2 batteries create obstacles for practical applications of Li/Na–CO2 batteries. Recently, earth‐abundant potassium ions have attracted considerable interest as fast ionic charge carriers for electrochemical energy storage. Herein, we report the first K–CO2 battery with a carbon‐based metal‐free electrocatalyst. The battery shows a higher theoretical discharge potential (E⊖=2.48 V) than that of Na–CO2 batteries (E⊖=2.35 V) and can operate for more than 250 cycles (1500 h) with a cutoff capacity of 300 mA h g−1. Combined DFT calculations and experimental observations revealed a reaction mechanism involving the reversible formation and decomposition of P121/c1‐type K2CO3 at the efficient carbon‐based catalyst.

Two-dimensional diamine-linked covalent organic frameworks for CO2/N2 capture and separation: theoretical modeling and simulations.

Two-dimensional covalent organic frameworks (2D-COFs) with diamine-based linkers have been designed and investigated for CO2/N2 gaseous mixture adsorption and separation via a systematic theoretical study by combining density functional theory (DFT) calculations and force field-based molecular dynamics (MD) simulations. We explored the adsorption sites and adsorption energies of CO2/N2 on 2D-COFs. The gas uptake capacity, adsorption isotherms, permeability, and selectivity were simulated based on an improved formulation of force fields for mixture separation in post-combustion conditions. This theoretical approach provided atomistic understanding and quantitative description of intermolecular interactions governing the physisorption dynamics of the considered systems. The results suggest that 2D-COFs investigated in this study are competitive with other 2D materials for carbon capture and separation and can be considered as alternative molecular sieving materials offering efficient and rapid separation and adsorption of different molecules.

Probing the 91Zr NMR parameters in the solid state by a combination of DFT calculations and experiments

The practical level of accuracy of the plane-waves (PW) DFT calculations of the 91Zr chemical shielding (CS) and electric field gradient (EFG) solid-state NMR parameters has been thoroughly investigated to aid in structural studies of crystalline zirconium-containing systems. The CS and EFG data have been shown to be reliably described over wide ranges of benchmarking values by PW DFT calculations with an approximate inclusion of relativistic effects. Based on this, the 91Zr CS scale has been proposed, and the La2Zr2O7 pyrochlore has been investigated theoretically in terms of spatial orientations of its 91Zr CS and EFG tensors.

Facet-Dependent of Catalytic Selectivity: The Case of H2O2 Direct Synthesis on Pd Surfaces

Pd catalysts display excellent potential applications in H2O2 direct synthesis from H2 and O2. Facet dependence on catalytic selectivity for H2O2 direct synthesis on Pd surfaces is investigated by the combination of DFT calculations and microkinetic study. It is found that the coadsorbed O plays a key role in catalytic activity and selectivity for H2O2 direct synthesis on Pd(111) and Pd(100) surfaces. The coadsorbed O on Pd surfaces could not only increase the catalytic activity but also promote the catalytic selectivity on Pd surfaces. With the help of coadsorbed O, Pd(111) surface shows a very high selectivity (>99%) for H2O2 products, but Pd(100) surface displays a high selectivity (>99%) for H2O formation. The role of proton transfer is also investigated in H2O2 direct synthesis, and it is found that proton transfer reactions are harmful to H2O2 formation. This work sheds light on the reaction mechanism of H2O2 direct synthesis reaction on different Pd surfaces, and it may create a new path to underst...

The use of ferrites as highly active oxygen storage materials for chemical looping hydrogen production under intermediate temperature

Shifting chemical looping from high temperatures to intermediate temperatures could mitigate the materials from sintering and benefit for longer durability as well as process economy. However, oxygen carriers cannot perform sufficiently due to the degrading effect at lower temperatures, resulting in the decrease of hydrogen production ability. Although doping precious metals can improve the poor performance at intermediate temperatures, the high cost impeded their large-scale application. In this paper, a range of oxygen carrier materials consisted of earth abundant elements were prepared for chemical looping hydrogen production. The results indicated that CoFe2O4 exhibited the highest hydrogen yield of 11.9 mmol·g−1 and hydrogen production rate of 0.051 mmol g−1·s−1 at 650 °C, which was 1.7 times higher than that of Fe2O3. A combined experimental and DFT calculation method was used to understand the mechanism behind the performance. The results indicated that the synergistic effect between Co and Fe increased the reactivity of the ferrite materials. The enhanced hydrogen production performance was attributed to the high reduction degree and reversible phase change. This study can be also extended to develop more active oxygen carrier for chemical looping processes at intermediate temperatures.

Pd-TiO2 Schottky heterojunction catalyst boost the electrocatalytic hydrodechlorination reaction

Electrocatalytic hydrodechlorination (EHDC) provides one promising solution to mitigate challenges from the water pollutions by persistent chlorinated organics. Palladium (Pd) has shown appealing properties as EHDC catalysts, while the low earth abundance has urged us to raise its activity and minimize usage. Herein, one novel semiconductor-metal Pd-TiO2 Schottky heterojunction catalyst was developed, which notably outperformed the conventional Pd-C catalyst in mass activity, dechlorination degree and energy selectivity towards EHDC of 2,4-dichlorophenol (2,4-DCP) in water. A combined experimental and DFT calculation study on mechanism revealed that the primary product phenol had a considerable negative effect on EHDC by competing the active sites with 2,4-DCP. The enhanced performance of Pd-TiO2 originated from the Schottky heterojunction-induced metal-support interactions, which optimized the Pd electronic structure and balanced the 2,4-DCP adsorption and phenol desorption on Pd. This study highlights one novel strategy to boost the metal performance in electrocatalytic hydrogenation reactions.

A highly selective tin-copper bimetallic electrocatalyst for the electrochemical reduction of aqueous CO2 to formate

Electrochemical reduction of CO2 is promising for mitigating the excessive CO2 emission. However, the low efficiency and poor selectivity for targeted products block the practical application of most conventional electrocatalysts. Here, we developed an electronic regulation Cu embedded into Sn nanoparticles heterogeneous bimetallic catalyst, with high catalytic activity and selectivity for electrochemical reduction of CO2. The excellent performance of high activity is mainly due to the appearance of abundant Sn-Cu interfaces after Cu embedded into Sn nanoparticles. XPS characterization indicates that the atomic Sn electronic structure of the bimetallic catalyst was significantly regulated by deposited Cu atoms. DFT calculations in combination with In-situ Raman spectroscopy characterization on CO2 reduction process further indicates that the electronic regulation of bimetallic catalyst facilitates the formation of key intermediate HCOO • followed by the generation of formate with high selectivity. The present design provides a method for prepare bimetallic catalyst with high catalytic performance.

From the Terrace Contraction to the Hexameric Sulfur Phase in the Au(100) Surface: A Combined Density Functional Theory and Scanning Tunneling Microscopy Study

The lifting of the Au(100) quasi-hexagonal reconstruction by atoms or molecules leaves a rough surface with islands, terraces, and vacancies where different patterns of adsorbates can appear. Although the roughness of the (1 × 1)-Au(100) surface has been well characterized, to our knowledge, there are no theoretical studies considering its effect on the formation of adsorbate patterns, for instance, in the case of sulfur adsorption. In this study, we have combined DFT calculations and STM measurements to explore the structural effects induced on the terrace when the sulfur adsorption takes place on the island and vacancy. Models predict a decrease of the Au–Au bond length in the terrace if the terrace has an appropriate size when the simultaneous adsorption of the sulfur structure (2×2) occurs on the island and vacancy. According to our predictions, this process of gold bond length contraction on the terrace can affect the formation of the sulfur structure on it. STM images reveal regions where the (2×2) ...

Cyclohexanehexone with Ultrahigh Capacity as Cathode Materials for Lithium-Ion Batteries.

Organic carbonyl compounds show potential as cathode materials for lithium-ion batteries (LIBs) but the limited capacities (<600 mA h g-1 ) and high solubility in electrolyte restrict their further applications. Herein we report the synthesis and application of cyclohexanehexone (C6 O6 ), which exhibits an ultrahigh capacity of 902 mA h g-1 with an average voltage of 1.7 V at 20 mA g-1 in LIBs (corresponding to a high energy density of 1533 Wh kg-1 ). A preliminary cycling test shows that C6 O6 displays a capacity retention of 82 % after 100 cycles at 50 mA g-1 because of the limited solubility in high-polarity ionic liquid electrolyte. Furthermore, the combination of DFT calculations and experimental techniques, such as Raman and IR spectroscopy, demonstrates the electrochemical active C=O groups during discharge and charge processes.

Cyclohexanehexone with Ultrahigh Capacity as Cathode Materials for Lithium‐Ion Batteries

AbstractOrganic carbonyl compounds show potential as cathode materials for lithium‐ion batteries (LIBs) but the limited capacities (&lt;600 mA h g−1) and high solubility in electrolyte restrict their further applications. Herein we report the synthesis and application of cyclohexanehexone (C6O6), which exhibits an ultrahigh capacity of 902 mA h g−1 with an average voltage of 1.7 V at 20 mA g−1 in LIBs (corresponding to a high energy density of 1533 Wh kg−1 ). A preliminary cycling test shows that C6O6 displays a capacity retention of 82 % after 100 cycles at 50 mA g−1 because of the limited solubility in high‐polarity ionic liquid electrolyte. Furthermore, the combination of DFT calculations and experimental techniques, such as Raman and IR spectroscopy, demonstrates the electrochemical active C=O groups during discharge and charge processes.

Interplay Between Site Activity and Density of BCC Iron for Ammonia Synthesis Based on First‐Principles Theory

AbstractSite activity and density are two key factors in determining the overall activity of catalysts in heterogeneous catalysis. Combined DFT calculation, Wulff construction and micro‐kinetic analysis, we reveal here a significant interplay between site activity and density of bcc iron catalyzed ammonia synthesis at low coverage regime. It is found that for large size particles, Fe (111) and (311) surfaces that consist of active C7 sites are limited by their low site density, whereas those with the most abundant sites are limited by their low activity. In contrast, Fe (221), (211) and (310) surfaces which consist of active C7 and/or B5 sites and remain abundant, dominate the overall reaction rate, turn‐over‐frequency and mass specific activity. Turn‐over‐frequency of the smaller Fe particles (2–6 nm) decreases by a factor of two or three due to the absence of (221) surface. For the particle size less than 2 nm, the corresponding activity decreases dramatically owing to the absence of all active C7 and/or B5 sites. Interplay of site abundance and intrinsic activity of catalysts is highlighted, and the insights revealed could be used to design and develop better catalysts for ammonia synthesis and other important reactions of technological interest.

Conformational studies of bipyrimidine-based mesogens by combination of DFT calculations and temperature-dependent infrared studies

ABSTRACTCombination of DFT calculations and solid-state temperature-dependent infrared spectroscopy has confirmed that the central core of recently developed bipyrimidine-based mesogens is not flat, i.e. do not adopt a disc shape, inside the columnar liquid-crystalline phase. For this purpose, the intensities and the frequency shifts of the most sensitive C–N and C–C bands of the central bipyrimidine core have been studied as a function of the temperature and of the dihedral angle. The results support the reported packing model in which the molecules are interdigitated alternatively along their long axis and their short axis to form columns inside the mesophase.

Glutathione activation of an organometallic half-sandwich anticancer drug candidate by ligand attack.

In contrast to the clinical drug cisplatin, the anticancer complex [Os(η6-p-cymene)(4-(2-pyridylazo)-N,N-dimethylaniline)I]+ [1-I] is inert towards hydrolysis and targets cancer cell metabolism rather than DNA. A combination of DFT calculations and X-ray absorption spectroscopy (XAS) suggests that hydrolytic activation of 1-I involves catalytic attack by the intracellular tripeptide glutathione (GSH) on the azo bond of the chelating ligand in the complex.

Reactions of the organoplatinum complex [Pt(cod) (neoSi)Cl] (neoSi = trimethylsilylmethyl) with the non-coordinating anions SbF6– and BPh4–

Abstract Reactions of the organoplatinum complex [Pt(cod)(neoSi)Cl] (neoSi = (trimethylsilylmethyl) with the Ag(I) salts of oxo or fluoride containing anions A– = NO3 –, ClO4 –, OTf – (trifluoromethanesulfonate) and SbF6 – lead to the desired abstraction of the chlorido ligand and precipitation of AgCl. However, further reaction of the resulting Pt complexes [Pt(cod)(neoSi) (solvent)]+ with diverse N-heterocyclic ligands L such as pyridines, caffeine, and guanine did not yield the targeted complexes [Pt(cod)(neoSi)(L)](A) in most of the cases, but to extensive decomposition yielding [Pt(cod)(Me) (solvent)]+, thus transforming the neoSi into a methyl ligand. A detailed study on the reaction with SbF6 – combining DFT calculations with NMR and MS revealed that Pt catalysed decomposition of SbF6 ‒ and fluorination of the neoSi silicon atom leading to FSiMe3. When reacting the parent complex with Ag(BPh4), the arylated derivative [Pt(cod)(neoSi)(Ph)] was obtained and characterised by multinuclear NMR, MS and single crystal XRD.

Application of combined solid-state NMR and DFT calculations for the study of piracetam polymorphism

Piracetam, a popular nootropic drug, widely used in the treatment of age-associated mental decline and disorders of the nervous system such as Alzheimer's disease and dementia exists under normal pressure in three polymorphic forms (P1, P2 and P3) of different stability. In this work the relative stability of piracetam polymorphs depending on the temperature was studied using the ssNMR spectroscopy combined with ab initio DFT calculations. The ssNMR spectroscopy enabled the analysis of polymorphic phase transition in the case of pure active substance as well as polymorphic form identification in the analysis of the commercial solid dosage formulations. Quantum chemical calculations of phonon density of states were performed to obtain the temperature dependence of the enthalpy, entropy and free energy of the piracetam polymorphs in a quasi-harmonic approximation. GIPAW NMR calculations combined with molecular dynamics were performed to support the chemical shift assignment. The obtained results showed that DFT calculations can be used not only to obtain the NMR parameters but also to predict the influence of the temperature on the stability order of the polymorphic forms of molecular crystals.

Anion intercalated layered-double-hydroxide structure for efficient photocatalytic NO remove

Due to the easily controllable interlayer anions, metal cation composition proportion and thickness, which is beneficial to modify surface chemical state and tune bandgap, layered double hydroxides (LDHs) have great promising potential for photocatalytic applications. In this study, we have successfully synthesized the ZnAl–LDH intercalated the single anion between ZnAl cationic interlayer without anionic impurities by using a facile calcining and reconstructing routes. The electron structure and surface chemical state of the prepared products have been investigated by combining the DFT calculation and experimental characterization methods. UV–vis DRS was used to certify the light absorption of the prepared products, and we performed the DFT calculation to demonstrate the density of state and activation of reactant. These results suggested that the ZnAl–LDH–CO3 possessed the more proper band structure and superior ability to activate NO and O2 for accelerating the photocatalytic NO oxidation activity. Moreover, the in situ DRIFTS with dynamically monitoring intermediates and products over the ZnAl–LDH–CO3 was adopted to declare the photocatalytic NO oxidized process during the photocatalytic reaction process. This work illustrated the influence of different interlayer anions to the electron structure and surface chemical state of ZnAl–LDH structure through the experimental verification combined DFT calculation and the photocatalytic NO oxidized process via in situ DRIFTS analyzing, which would provide a novel way to design and fabricate the efficient photocatalysis, and understand the reaction process.

Tetrel Bonding Interactions in Perchlorinated Cyclopenta- and Cyclohexatetrelanes: A Combined DFT and CSD Study.

In this manuscript, we combined DFT calculations (PBE0-D3/def2-TZVP level of theory) and a Cambridge Structural Database (CSD) survey to evaluate the ability of perchlorinated cyclopenta- and cyclohexatetrelanes in establishing tetrel bonding interactions. For this purpose, we used Tr5Cl10 and Tr6Cl12 (Tr = Si and Ge) and HCN, HF, OH− and Cl− as electron donor entities. Furthermore, we performed an Atoms in Molecules (AIM) analysis to further describe and characterize the interactions studied herein. A survey of crystal structures in the CSD reveals that close contacts between Si and lone-pair-possessing atoms are quite common and oriented along the extension of the covalent bond formed by the silicon with the halogen atom.

Dry reforming of methane over CeO2-supported Pt-Co catalysts with enhanced activity

Dry reforming of methane provides opportunities of using CH4 and CO2 to produce syngas. The PtCo/CeO2 bimetallic catalyst shows higher activity and H2/CO ratio than the corresponding monometallic catalysts, mainly attributed to the synergistic effect of Pt-Co. Structural feature of the PtCo/CeO2 catalyst was revealed by diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) of adsorbed CO and in situ techniques like X-ray diffraction (XRD), X-ray adsorption fine structure (XAFS) and ambient-pressure X-ray photoelectron spectroscopy (AP-XPS). Pt-Co alloy and separated Co particles co-existed in the bimetallic catalyst, whereas the former was determined as the dominant active structure with a Pt-Co-mixed-surface termination. During reaction, Pt and Co in the alloy structure nearly maintained their metallic state with slight oxygen decoration, yielding oxygen-metal site-pairs (O*-*). Combined kinetic investigations and DFT calculations reveal that the O*-modified catalytic surface of PtCo/CeO2 promotes CH bond activation with higher entropy contribution (less constraints) to compensate its higher activation barrier. Thermogravimetric analysis (TGA), transmission electron microscope (TEM) and Raman spectroscopy show that the PtCo/CeO2 catalyst is resistant to coke formation as effectively as Pt/CeO2 and can be easily regenerated by a mild CO2 treatment.

First Principles Calculation of the Reaction Rates for Ligand Binding to Myoglobin: The Cases of NO and CO.

Ligand binding by proteins is among the most fundamental processes in nature. Among these processes the binding of small gas molecules, such as O2 , CO and NO to heme proteins has traditionally received vivid interest, which was further boosted by their recently recognized significant role in gas sensing in the body. At the heart of the binding of these ligands to the heme group is the spinforbidden reaction between high-spin iron(II) and the ligand yielding a low-spin adduct. We use computational means to address the complete mechanism of CO and NO binding by myoglobin. Considering that it involves several steps occurring on different time scales, molecular dynamics simulations were performed to address the diffusion of the ligand through the enzyme, and DFT calculations in combination with statistical rate calculation to investigate the spin-forbidden reaction. The calculations yielded rate constants in qualitative agreement with experiments and revealed that the bottleneck of NO and CO binding is different; for NO, diffusion was found to be rate-limiting, whereas for CO, the spin-forbidden step is the slowest.

In Situ Formation of PBiP Ligands upon Complexation of a Mixed Phosphane/Bismuthane with Group 11 Metal Ions

The behavior of a xanthene derivative with one bismuthane and one phosphane function, Xan(PPh2)(BiPh2), as a ligand toward group 11 metal cations was investigated. It was found that contact with [Cu(MeCN)4]OTf, AgOTf, [Au(PPh3)OTf], in all three cases leads to a transformation of Xan(PPh2)(BiPh2) into a tridentate PBiP system, where a BiPh unit connects two phosphinoxanthyl moieties. In the resulting compounds, [PhBi(Xan(PPh2))2Cu]OTf, 1, [PhBi(Xan(PPh2))2Ag]OTf, 2, and [PhBi(Xan(PPh2))2AuPPh3]OTf, 3, the metal cations are coordinated tetrahedrally by two phosphane donors, one bismuthane donor and a fourth ligand, corresponding to OTf– in case of 1 and 2, or PPh3 in the case of 3. DFT calculations in combination with NBO analysis showed that the bismuth atoms in these PBiP ligands act as σ-donors. 3 thus corresponds to the first known AuI ← BiIII complex.