Negligible Energy Barrier Research Articles

A comparative theoretical study: Reaction mechanism of Hg0 and H2S/H2Se on α-Fe2O3 (0 0 1) surface

Selenium has emerged as a modifier of mercury sorbent in recent years following sulfur, and H2Se is expected to be helpful for mercury capture as H2S do. To explore the differences in the impact of H2S and H2Se on mercury control, the reaction mechanism of Hg and H2S/H2Se on the α-Fe2O3(0 0 1) surface was investigated by density functional calculations. The results show that the H2S and H2Se perform similar adsorption behaviors on α-Fe2O3 (0 0 1) surface, and they tend to undergo a complete dissociative adsorption, with H atoms bonding to surface O atoms, and S/Se atoms bonding to surface Fe atoms. Comparatively, the adsorption of H2Se is more favorable than H2S in both thermodynamics and kinetics. The active S/Se site, derived from the dissociative adsorption of H2S/H2Se, can stabilize Hg atoms firmly through the generation of HgS/HgSe with a negligible energy barrier. However, HgS and HgSe are unlikely to desorb from α-Fe2O3 (0 0 1) surface indicated by their high adsorption energy of above 320 kJ/mol. These findings not only elucidate the reaction mechanisms involved in the interaction between H2Se and mercury on the α-Fe2O3 (0 0 1) surface but also predict the superior performance of H2Se compared to H2S in enhancing mercury capture over sorbents.

Catalytic Mechanism of Formate Dehydrogenase: Does Rotation of Formate Provide the Impetus for Surmounting the Activation Energy Barrier?

AbstractFormate oxidation by Candida boidinii formate dehydrogenase was recently subjected to QM/MM MD simulations (Q. Guo et al., Biochemistry 55, 2016, 2760–2771). Inspection of snapshots from the reported umbrella sampling of the reactants state region provided two interesting observations. Firstly, an ester bond between formate and nicotinamide spontaneously formed and subsequently dissociated. Such an ester adduct was previously predicted to form with negligible energy barrier in gas phase but was so far not reported in QM/MM MD simulations. Secondly, two snapshots were identified as possible near‐attack conformations (NACs) from which the transition state (TS) can be reached by unhindered rotation of formate about its O─O axis. The NACs differ from each other in the direction of rotation required to attain TS. Calculation of natural orbitals for chemical valence channels indicated genesis of the new C─H bond already at the NAC stage. Both NACs feature a nonlinear C(formate)–H(formate)–C(nicotinamide) angle, approaching linearity only in the TS. We believe that due to the particular conception of the active site which profits from the unique triangular shape of the substrate, the formate ion can reach the TS more easily through this rotational movement than through parallel shift along the C─H vector, as previously assumed.

Origin of Deformation Twinning in bcc Tungsten and Molybdenum.

Twinning is profuse in bcc transition metals (TMs) except bulk W and Mo. However, W and Mo nanocrystals surprisingly exhibit twinning during room temperature compression, which is completely unexpected as established nucleation mechanisms are not viable in them. Here, we reveal the physical origin of deformation twinning in W and Mo. We employ density functional theory (DFT) and a reduced-constraint slip method to compute the stress-dependent generalized stacking fault enthalpy (GSFH), the thermodynamic quantity to be minimized under constant loading. The simple slipped structures and GSFH lines show that compressive stresses stabilize a two-layer twin embryo, which can grow rapidly via twinning disconnections with negligible energy barriers. Direct atomistic simulations unveil the explicit twinning path in agreement with the DFT GSFH lines. Twinning is thus the preferred deformation mechanism in W and Mo when shear stresses are coupled with high compressive stresses. Furthermore, twinnability can be related to the elastic constants of a stacking fault phase (SFP). The hcp phase may serve as a candidate SFP for the {112}⟨1[over ¯]1[over ¯]1⟩ twinning system in bcc TMs and alloys, which is coincident with the {111}⟨112[over ¯]⟩ twinning in fcc structures.

Chemical Bonding and Dynamic Structural Fluxionality of a Boron-Based Na5B7 Sandwich Cluster.

Doping alkali metals into boron clusters can effectively compensate for the intrinsic electron deficiency of boron and lead to interesting boron-based binary clusters, owing to the small electronegativity of the former elements. We report on the computational design of a three-layered sandwich cluster, Na5B7, on the basis of global-minimum (GM) searches and electronic structure calculations. It is shown that the Na5B7 cluster can be described as a charge-transfer complex: [Na4]2+[B7]3-[Na]+. In this sandwich cluster, the [B7]3- core assumes a molecular wheel in shape and features in-plane hexagonal coordination. The magic 6π/6σ double aromaticity underlies the stability of the [B7]3- molecular wheel, following the (4n + 2) Hückel rule. The tetrahedral Na4 ligand in the sandwich has a [Na4]2+ charge-state, which is the simplest example of three-dimensional aromaticity, spherical aromaticity, or superatom. Its 2σ electron counting renders σ aromaticity for the ligand. Overall, the sandwich cluster has three-fold 6π/6σ/2σ aromaticity. Molecular dynamics simulation shows that the sandwich cluster is dynamically fluxional even at room temperature, with a negligible energy barrier for intramolecular twisting between the B7 wheel and the Na4 ligand. The Na5B7 cluster offers a new example for dynamic structural fluxionality in molecular systems.

Atomic-scale de-passivation mechanisms of anatase TiO2 induced by corrosive halides based on density-functional theory

By using density-functional theory calculations, we systematically investigated the localized corrosion behavior of anatase TiO2 by chloride (Cl)/fluoride (F) via different mechanisms. Energetics for adsorption and substitution pointed to a more aggressive influence of F over Cl, revealing that F was more likely to induce TiO2 de-passivation by “adsorption-thinning” mechanism, though surface hydroxylation can promote Cl etching via this mechanism. Whereas Cl accessed to TiO2 interior with nearly negligible diffusion energy barrier, facilitated by dramatic relaxations via mechanism of Cl residing at oxygen vacancies (VO), accompanied by a reduction in passivity. Moreover, the annihilation/creation of VO at the TiO2 (101) surface was dominated by competition of adsorbed species. While a subsurface VO can move towards the outermost surface by exchanging with lattice O, a surface VO can spontaneously re-combine with a surface O promoting re-passivation. Co-adsorption of Cl/F with O can significantly inhibit VO–O combination by directly occupying the VO site or by reducing the energy to create a VO. Our studies outlined the non-negligible interactions between corrosive species and defects in TiO2 and the mechanisms concerning Cl/F/O inducing re(de)-passivation, the understanding of which is meaningful in mitigating Ti corrosion in environments containing halides.

Potential of Single Transition Metal Atom Embedded C2N as Efficient Catalysts for N2O Reduction: Theoretical Investigation

AbstractConverting the toxic air pollutant N2O into less harmful gas has potential advantages. Herein, the feasibility of the N2O reduction reaction over pristine C2N and TM/C2N (TM = V, Cr, Mn, Fe, Co, Ni, Cu, and Zn) monolayers are explored by density functional theory calculations with Grimme‐D3 correction. The results reveal that the existence of TM atoms indeed improves the adsorption performance of C2N, where the TM atoms act as both electron acceptors and donors, favoring the activation of N2O and CO molecules. Based on thermal stability, selectivity, and catalytic activity, TM/C2N (TM = V and Mn) catalysts are screened from the above transition metal atoms. In particular, N2O reduction is a thermodynamically and kinetically favorable pathway, which can take place with negligible energy barriers on V/C2N and Mn/C2N catalysts. The CO2 desorption on V/C2N and Mn/C2N catalysts is the rate‐limiting step with the desorption barrier of only 13.1 and 15.1 kcal mol−1, respectively. These results suggest that the screened TM/C2N (TM = V and Mn) materials can be used as promising catalysts for the adsorption and reduction of environmentally unfriendly N2O molecules.

Insight into the direct conversion of methane to methanol on modified ZIF-204 from the perspective of DFT-based calculations.

Direct oxidation of methane over oxo-doped ZIF-204, a bio-mimetic metal-organic framework, is investigated under first-principles calculations based on density functional theory. In the pristine ZIF-204, the tetrahedral methane molecule anchors to an open monocopper site via the so-called η2 configuration with a physisorption energy of 0.24 eV. This weak binding arises from an electrostatic interaction between the negative charge of carbon in the methane molecule and the positive Cu2+ cation in the framework. In the modified ZIF-204, the doped oxo species is stabilized at the axial position of a CuN4-base square pyramid at a distance of 2.06 Å. The dative covalent bond between Cu and oxo is responsible for the formation energy of 1.06 eV. With the presence of the oxo group, the presenting of electrons in the O_pz orbital accounts for the adsorption of methane via hydrogen bonding with an adsorption energy of 0.30 eV. The methane oxidation can occur via either a concerted direct oxo insertion mechanism or a hydrogen-atom abstraction radical rebound mechanism. Calculations on transition-state barriers show that reactions via the concerted direct oxo insertion mechanism can happen without energy barriers. Concerning the hydrogen-atom abstraction radical rebound mechanism, the C-H bond dissociation of the CH4 molecule is barrierless, but the C-O bond recombination to form the CH3OH molecule occurs through a low barrier of 0.16 eV. These predictions suggest the modified ZIF-204 is a promising catalyst for methane oxidization.

Electron deficient boron-doped amorphous carbon nitride to uphill N2 photo-fixation through π back donation

The photocatalytic Nitrogen fixation to NH3 by using water as a protonation source is a requisite renovation for life. Albeit, the activation and adsorption of robust NN is the bottleneck in NH3 synthesis. Here, we report an amorphous-wrinkled hollow-tubular electron-deficient boron-doped carbon nitride (BCN) for improved photocatalytic N2 fixation via “σ donation and π back donation”. The electron-deficient B played synergetic roles to activate and stabilize the adsorbed N2 i.e. (i) It tunes the bandgap of CN for effective light absorption and charge transfer; (ii) The B-N coordination site polarizes chemisorbed N2 via electron pair acceptance; (iii) The filled sp2 orbital of B activates the N2 by π-back donation. Consequently, the photocatalytic performance of BCN-4 reaches 0.93mmolh−1g−1 with AQY of ∼13% (350 nm) and solar to NH3 conversion efficiency (SSCNH3) of 0.017%. The in situ DRIFT and DFT studies revealed that BCN exhibited spontaneous N2 adsorption and activation, followed by protonation of the adsorbed N2, with a negligible energy barrier.

High-Throughput Computational Exploration of MOFs with Open Cu Sites for Adsorptive Separation of Hydrogen Isotopes.

Effective separation of hydrogen isotopes still remains one of the extremely challenging tasks in industry. Compared to the present methods that are energy- and cost-intensive, quantum sieving technology based on nanostructured materials offers a more efficient alternative approach, where metal-organic frameworks (MOFs) featuring open metal sites (OMS) can serve as an ideal platform. Herein, a combination of periodic density functional theory (DFT) with dispersive correction and high-throughput molecular simulation was employed from thermodynamic viewpoints to explore the D2/H2 separation properties of 929 experimental MOFs bearing a copper-paddlewheel unit. The DFT calculations showed that there is a negligible rotational energy barrier for the molecule adsorbed at the OMS, and the movement of the Cu atoms along the Cu-Cu axis vector almost has no influence on the interaction energy. On the basis of the DFT results, a new force field with a proposed cutoff scheme was developed to accurately describe the strong isotope-OMS interaction. Under practical conditions (40 K and 1.0 bar), large-scale computational material screening demonstrated that the OMS interaction plays a more important role in highly selective materials and ignoring such interactions can lead to completely wrong identification of the most promising materials. Using the adsorption selectivity and adsorbent performance score as evaluation metrics, this work demonstrated that the materials with sql topology notably outperform many benchmark adsorbents reported so far.

Enhanced thermoelectric properties of polycrystalline CuCrS2−x Se x (x = 0, 0.5, 1.0, 1.5, 2) samples by replacing chalcogens and sintering

The optimization of thermoelectric properties of the CuCrSSe x (x = 0, 0.5, 1.0, 1.5, 2) samples was achieved by substitution in anionic sublattice and sintering at high temperature. The maximum power factor PF ∼ 0.3 mW (m·K)−2 among a series of samples with chalcogen substitution was obtained for CuCrS0.5Se1.5 sample at T = 300 K. The sintering made it possible to obtain the maximum value PF ∼ 2.1 mW (m·K)−2 for CuCrSe2 sample. This is due to a more than threefold increase in the thermopower S(T) in CuCrSe2 sample with a spin-orbital interaction in comparison with CuCrS0.5Se1.5 sample with the same optimal electrical conductivity σ ( 100 S cm−1), but without spin-orbital interaction. In CuCrSe2 sample, sintering effectively reduced the σ to an optimal value, suppressed of the magnetic phase transition in the range of 50–100 K, and the weak localization were replaced by weak antilocalization indicating the appearance of strong spin-orbit interaction below 20 K. As a result, an additional contribution to the S(T) appeared due to the filtration of current carriers caused by the strong spin-orbit interaction. The effect of grain boundaries on the properties σ and S(T) of the samples was investigated. It was established that polycrystalline samples with a high sulfur content were low-conductivity materials consisting of high-conductivity crystallites with the charge carriers concentration cm−3 separated by low-conductivity grain boundaries with fluctuation-induced tunneling conductivity. Both the replacement of sulfur with selenium and sintering led to a decrease in the energy barriers connecting grain boundaries. Selenium-dominated samples (CuCrS0.5Se1.5 and CuCrSe2) had high electrical conductivity with negligible energy barriers between grain boundaries. Logarithmic quantum corrections to the electrical conductivity was observed below 20 K, which indicated a quasi-two-dimensional electron transport in these samples.

Enhanced Activation of CO2 on h-BN Nanosheets via Forming a Donor–Acceptor Heterostructure with 2D M2X Electrenes

The activation of CO2 is the first crucial step in the CO2 reduction reaction (CO2RR), but it faces the challenge of the ultrahigh chemical stability of the CO2 molecule. Two-dimensional (2D) hexagonal boron nitride (h-BN) has been considered as a promising electrocatalytic interface material due to its high specific surface area, N- and B-active sites, and adjustable chemical reactivity through interactions with other materials. Here we report a donor–acceptor heterostructure (DAH) containing 2D h-BN and M2N (M = Ca, Sr, and Ba) or Y2C electrene, single-layer electride materials, toward the activation of the CO2 molecule on the basis of first-principles calculations. Our results demonstrate that a considerable number of electrons (0.1 e per BN unit) transfer from M2X electrene to the h-BN sheet due to the strong electrostatic interaction between the cation boron in the h-BN sheet and the anion electron gas in M2X electrides, which significantly enhances the CO2 activation activity of the h-BN monolayer. The adsorption of CO2 on h-BN is exothermic, with a negligible energy barrier down to 0.013 eV. Meanwhile, the overpotential of the hydrogenation of CO2 to HCOOH is as low as 0.17 V on the h-BN/Y2C DAH, implying superior performance for the CO2 reduction on the h-BN/M2X DAH. This work provides a strategy for activating CO2 on the h-BN monolayer by building a DAH with 2D electride materials.

Rapid soot inception via α-alkynyl substitution of polycyclic aromatic hydrocarbons

Soot particles alter global climate and dominate the origin and evolution of carbonaceous interstellar material. Convincing experimental evidence has linked polycyclic aromatic hydrocarbons (PAH) to soot inception under low-temperature astrochemistry and high-temperature combustion conditions. However, significant gaps still remain in the knowledge of PAH and soot formation mechanisms. Here, we report theoretical and experimental evidence for a soot inception and growth pathway driven by peri-condensed aromatic hydrocarbons (PCAH) with an alkynyl substitution. Initially, free radicals attack the α-alkynyl substitution of PCAHs to form covalently bound compounds yielding resonantly stabilized radicals (RSRs), which promote further clustering through repeated addition reactions with negligible energy barriers. The proposed pathway is shown to be competitive at temperatures relevant to astrochemistry, engine exhaust manifold and flames because it does not require H-abstraction reactions, the requisite reaction precursors are in abundance, and the reaction rate is high. Such addition reactions of PCAHs with α-alkyne substituents create covalently bound clusters from moderate-size PAHs that may otherwise be too small to coagulate.

Substituent effects on the photophysical properties of 2,9-substituted phenanthroline copper(I) complexes: a theoretical investigation.

The electronic and nuclear structures of a series of [Cu(2,9-(X)2 -phen)2 ]+ copper(I) complexes (phen=1,10-phenanthroline; X=H, F, Cl, Br, I, Me, CN) in their ground and excited states are investigated by means of density functional theory (DFT) and time-dependent (TD-DFT) methods. Subsequent Born-Oppenheimer molecular dynamics is used for exploring the T1 potential energy surface (PES). The T1 and S1 energy profiles, which connect the degenerate minima induced by ligand flattening and Cu-N bond symmetry breaking when exciting the molecule are calculated as well as transition state (TS) structures and related energy barriers. Three nuclear motions drive the photophysics, namely the coordination sphere asymmetric breathing, the well-documented pseudo Jahn-Teller (PJT) distortion and the bending of the phen ligands. This theoretical study reveals the limit of the static picture based on potential energy surfaces minima and transition states for interpreting the luminescent and TADF properties of this class of molecules. Whereas minor asymmetric Cu-N bonds breathing accompanies the metal-to-ligand-charge-transfer re-localization over one or the other phen ligand, the three nuclear movements participate to the flattening of the electronically excited complexes. This leads to negligible energy barriers whatever the ligand X for the first process and significant ligand dependent energy barriers for the formation of the flattened conformers. Born-Oppenheimer (BO) dynamics simulation of the structural evolution on the T1 PES over 11 ps at 300 K confirms the fast backwards and forwards motion of the phenanthroline within 200-300 fs period and corroborates the presence of metastable C2 structures.

Strategy Used to Control the Mechanism of Homogeneous Alkyne/Olefin Hydrogenation: AIMD Simulations and DFT Calculations.

Understanding the mechanism of the catalytic reaction is an effective way to design new high-performance catalysts. The mechanisms of alkyne/olefin hydrogenations catalyzed by a nonclassical Co-N2 catalyst are explored by ab initio molecular dynamics simulations and density functional theory calculations. From the calculated results, the hydrogenation mechanisms, i.e., molecular or atomic mechanisms, can be effectively controlled via employing the different interaction between the catalyst and substrates. The origination of excellent selectivity toward E-olefins for the Co-N2 catalyst is also taken into account with the help of investigating the olefin hydrogenation process. The mechanism indicates that the negligible energy barrier of rotation is the main reason for highly selective semihydrogenation of a Co-N2 catalyst, which leads to the trans-olefin formation. These investigations may provide some useful information and guidelines on the current understanding of the hydrogenation reaction and designing the high-performance catalysts.

In-situ hydrogen production and storage in (0 0 2) oriented TiO2 thin films

Hydrogen production and in-situ storage from water splitting is an attractive technology for clean energy. Here (0 0 2) oriented rutile TiO2 thin films are prepared by the hydrothermal method for photocatalytic water splitting. The H2O molecule efficiently dissociates on the high energy rutile (0 0 2) surface and the highest hydrogen production rate of 28.4 mmol h−1 g−1 is achieved in the film with the lowest density, at a rate comparable to powder TiO2 photocatalysts. The produced hydrogen is stored in-situ in the films with the help of the atomic hydrogen concentration difference between the surface and in the crystal lattice. Theoretical calculations show that water is dissociated on the rutile (0 0 2) surface with a negligible energy barrier. Hydrogen atoms diffused into the sublayers are confined in the TiO2 lattice owing to a high energy barrier for them to overcome to escape from the rutile (1 1 0) surface. The theoretical storage capacity is up to 1.2%, at room temperature and atmospheric pressure, demonstrating the potential for practical room-temperature hydrogen production and storage.

Synthesis and characterization of metallic sulfide NPs doped graphene oxide for methylene blue adsorption to leuco methylene blue in aqueous mixture

Introduction: The Metal Sulfide Nanoparticles Doped Graphene Oxide Sheets Have Been Studied And Were Used To Adsorb Fluorescent Methylene Blue Dye. Such Mechanism Efficiently Reduces The Dyes And Their Fluorescent Pollutants Through The Positive And Negative Holes. The Metal Sulfide Doped Graphene Oxide Could Be A Most Potential Route To Reduce From Fluorescent To Non-Fluorescent Species To Prevent The Global Warming And Other Pollution Being Caused By Them. Objectives: This Study Has Been To Strengthen And Widen The Applications Of Negative And Positive Holes Quick Formation At A Negligible Energy Barrier. Metal Sulfide Nanoparticles Were Doped With Graphene Oxide To Further Strengthen The Semiconducting And To Fastened The Rate Of Adsorption Of Methylene Blue Dye. Methods: Graphite Flakes Were Oxidized To Graphite Oxide With High Yield. The Graphite Oxide Was Sonicated In Water To Obtain Graphene Oxide And Doped With Metal Sulfide Nanoparticles In Situ. The Samples Were Characterized With High End Instruments And Used For Adsorption. Results: The Metal Sulfide Nanoparticles Were Successfully Doped With Graphene Oxide. The Ftir And Xps Spectra Infer Doping Of Metal Sulfide Nanoparticle In Graphene Oxide. That Enhanced Methylene Blue Adsorption Upto 97%. Conclusion: The Common Adsorption Effect Of Methylene Blue With Bare Graphene Oxide And Metal Sulfide Nanoparticles Doped Graphene Oxide Were Studied In This Paper. The Methylene Blue Adsorption Was Maximum (97%) By Cadmium Sulfide Doped Graphene Oxide Compared To Bare Graphene Oxide (87%), Nickel Sulfide Doped Graphene Oxide (79%), And Zinc Sulfide Doped Graphene Oxide (89%). The Metal Sulfide Nanoparticles Have Successfully Enhanced A Semiconductor Mechanism Of Graphene Oxide Especially With 3d And 4d10 Of Cds.

Hydrogen donation of bio-acids over transition metal facets: A density functional theory study

Bio-acids produced from biomass fast pyrolysis are regarded as alternative hydrogen source for upgrading bio-oil into transport fuels. In this work, the hydrogen donation performance of acetic acid (AcOH) and formic acid (FA) were evaluated over the transition metal facet in comparison with H2 gas, using Density Functional Theory (DFT) modelling. It was revealed that Mo (110) led to stronger binding with the bio-acid molecule than other base transition metals, and the consequent electrons migration significantly facilitated the bio-acids decomposition. AcOH exhibited a greater potential than FA as a hydrogen donor over Mo (110) because it released more H atoms with low energy barriers. H2 gas showed undoubtable merits of dissociative adsorption with negligible energy barrier over Mo (110). However, the larger enthalpy changes from the exothermic decomposition of bio-acids would probably more facilitate the activation and migration of the individual H atoms for their donation compared to H2 gas.

C59N Heterofullerene: A Promising Catalyst for NO Conversion into N2O

AbstractWe report, for the first time, the possibility of using N‐doped C60 fullerene (C59N) as a novel and highly active metal‐free catalyst for reduction of NO molecules to N2O. First‐principles density functional theory calculations are used to find the most energetically favorable adsorbed/coadsorbed configurations of NO molecules over C59N. Our results indicate that introducing a N impurity in C60 can induce a positive charge and large spin density over the carbon atoms nearest to the dopant atom. Consequently, these carbon atoms are identified as the most reactive sites to interact with the NO molecule. According to our results, the dissociation of NO molecule over C59N is almost impossible, due to its relatively high activation energy (1.35 eV). The reduction of NO over C59N starts with the coadsorption of two NO molecules to form (NO)2 species, followed by the dissociation of (NO)2 into N2O and an active atomic oxygen (Oads). The energy barrier to convert NO molecules into N2O ranges from 0.33 to 0.75 eV, which indicates this process is likely to proceed at normal temperature. Besides, by overcoming a negligible energy barrier (0.18 eV), the remaining Oads moiety can be easily eliminated by a CO molecule. To further understand the role of nitrogen atoms in the NO reduction process, the catalytic performance of high percentage N‐doped fullerene (C48N12) is also studied.

Symmetry and thermodynamics of tellurium vacancies in cadmium telluride

The equilibrium geometries and thermodynamic properties of anion vacancies in cadmium telluride, as predicted by density functional theory, are revisited using semilocal and hybrid density functionals. We find that stable configurations in different charge states can only be found after a systematic search considering several starting geometries. The stable charge states, 0 and 2+, display closed-shell electronic configurations, without deep bandgap levels. The 2+ charge state has a Td symmetry with an outward relaxation, while the neutral state is a mixture of configurations with C2v and C3v symmetries, both with the same energy and a negligible energy barrier. Therefore, the neutral charge state presents an effective Td symmetry. Configurations with different symmetries, e.g., D2d, can exist as metastable states. We show that certain configurations may seem falsely stable due to several facts: the bandgap error of generalized gradient approximation, the k-point sampling used in small supercells, or the use of a restricted set of starting geometries. We believe that the HSE06 hybrid functional allows to obtain accurate formation energies and geometries. We analyze the effect of the spin-orbit coupling and GW quasiparticle corrections to the HSE06 results, and find no qualitative differences. The spin-orbit coupling and GW corrections to the HSE06 energies partially cancel each other. Finally, we investigate the divacancy VCdVTe. The obtained formation energies suggest that isolated tellurium vacancies in neutral charge state can be found only in Te-poor growth conditions, coexisting with divacancies.

Mechanism, ab initio calculations and microkinetics of straight-chain alcohol, ether, ester, aldehyde and carboxylic acid hydrodeoxygenation over Ni-Mo catalyst

Hydrotreatment of bio-based model compounds was investigated in a three-phase slurry reactor over pre-sulphided NiMo/γ-Al2O3 bifunctional catalyst. Experimental results were supported by comprehensive in silico studies. Mathematical microkinetic model was developed for mass transfer phenomena, adsorption, desorption and surface kinetics description, while quantum chemical calculations were performed for the proposed reaction mechanism validation. Every moiety followed the same chemical reduction sequence as its predecessor down the oxidation ladder, except of aldehyde. Experiments using hexanal as a model compound resulted in its extraordinary high concentrations in liquid phase and on the catalyst surface, which led to mutual aldol condensation. However, this reaction was not observed when aldehyde was formed as an intermediate from hexanoic acid or methyl hexanoate, due to its low concentration and high hydrogen availability which promoted further hydrogenation into hexanol. C12/C6 (aldol condensation/hydrogenation) product ratio increased with higher temperature, reflecting higher activation energy (EA) for hexanal condensation compared to negligible hydrogenation energy barrier, confirmed by density functional theory (DFT) calculations. Primary alcohols are more resistant to HDO compared to secondary counterpart (studied in previous work) over NiMo/γ-Al2O3, specifically; the activation energy of 1-hexanol deoxygenation to olefin was 43% higher compared to secondary hexanols according to microkinetic model, and 45% higher according to quantum mechanics calculations. Primary alcohols are also extensively dehydrated into ethers, which was never the case for secondary alcohols at tested reaction conditions, while aldehydes are much easier to hydrogenate than ketones, which cannot undergo CC coupling reactions.