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Abstract: Adsorption of reaction intermediates appearing during CO hydrogenation at the sulfur covered MoS2(10−10) surfaces, Mo-termination with 42% S coverage and S-termination with 50% S coverage, are investigated systematically using periodic density functional theory methods. Computed vibrational frequencies of all intermediates are compared with observed data from infrared (IR) spectroscopy allowing a detailed interpretation and assignment of the different features in the experimental spectra. The pathway for CO hydrogenation on both terminations has been studied in detail where the most likely reaction path involves C1 type surface species in the sequence CO→CHO→CH2O→CH2OH→CH2 →CH3 →CH4 in agreement with the experiment. [Copyright &y& Elsevier]

B3LYP/6-31G* density functional theory calculations have been carried out on the structure and stability of seven B24N24 clusters. It is found that the new proposed isomer with two octagons, sixteen hexagons and eight squares in S8 symmetry is more stable than the isomer with six octagons, eight hexagons and twelve squares in O symmetry by 60.4 kcal/mol, and the isomer with twenty hexagons and six squares in S4 symmetry by 2.8 kcal/mol. The fullerene-like isomer is much higher in energy (148.6 kcal/mol). [Copyright &y& Elsevier]

Compares many nitrogen species and identifies pentazole derivatives as being the thermodynamically most stable polynitrogen compounds. Result of experiments on polynitrogen molecules at high levels of ab initio and density functional theory (DFT); Ab initio and DFT computations; Relative stability and geometry; Computed energetic increments for polynitrogen compounds.

Abstract: The structure and stability of azido azacycloalkanes, N n (N3) n (n =3–6), have been investigated at the B3LYP/cc-pvTZ level of density functional theory. The stability obeys the gauche effect. The most stable structure is N5(N3)5 (7), while N3(N3)3 (2) is the least stable structure. They are thermodynamically unstable towards dissociation into N2. [Copyright &y& Elsevier]

Abstract: The entire catalytic hydrodesulfurization (HDS) cycle of benzothiophene over Mo3S9 cluster has been investigated at the level of density functional theory. It is found that the hydrogenation and hydrogenolysis route with dihydrobenzothiophene (DHBT) as intermediate is more favored than the hydrogenolysis and hydrogenation route with styrene as intermediate. The stepwise hydrogenolysis of SB–C9 (C(aryl)–S) bond in DHBT leading to the formation of 2-phenylethanethiol is more favored than that of SB–C2 (C(alkyl)–S) bond with 2-ethylthiophenol as intermediate. The computed activation free energy and rate constant of benzothiophene hydrogenation to DHBT agree well with the available experimental data. The difference in HDS reactivity between benzothiophene and thiophene has been discussed. [Copyright &y& Elsevier]

Abstract: The structure and stability of endohedral X@Si20H20 complexes (X=Li0/+, Na0/+, K0/+, Be0/2+, Mg0/2+, Ca0/2+) have been studied at the B3LYP/6-31G* level of density functional theory. It is found that complexes with X=Na0/+, K0/+, Mg and Ca0/2+ are energy minimum structures with X at the cage center in Ih symmetry, while those with X=Li0/+, Be0/2+, Mg2+ have off-centered structures with X towards one pentagon face in C5v symmetry. Large electron or charge transfer between the Si20H20 cage and the encapsulated X has been observed. [Copyright &y& Elsevier]

Iron sulfides have emerged as a fascinating class of materials in electromagnetics and catalysis areas, which however are challenging in first-principles modeling because of the strongly-correlated interactions between Fe 3 d and S 3 p electrons. Here, we assess the performances of 14 density functionals on the structural, electronic, and magnetic properties of five iron sulfides. The PBE + U with U eff = 2.0 eV has the overall best performance. After evaluating functionals and obtaining reliable properties, our final goal is from predicting to correlating in order to do high throughput screening for the systems since the complex structures and phases of iron sulfides, to put it in another way, to hunting a reliable descriptor for predicting their properties. In the work, we demonstrate that the crystal orbital Hamilton population (COHP) and Bader charge of Fe atoms presents a good correlation with the empirical bond valence. Our results open a new avenue to effectively investigate phases and properties for various structures of iron sulfides. Indeed, the correlations between COHP/Bader charge and bond valence can be extended to other systems. [ABSTRACT FROM AUTHOR]

Abstract: During the last decade, an increased attention could be observed being paid on the use of renewables resources in the polymer and fine chemistry. Sunflower oil has been shown to be catalytically transformed into dimethyl 1,19-nonadecanedioate, using Pd/o-C6H4(CH2P t Bu2)2 as catalyst. This article presents a complete elucidation of the reaction mechanism and provides a detailed understanding of what makes this catalyst so active and selective for the combined transesterification/isomerization/methoxycarbonylation. Besides kinetic and density functional theory (DFT) treatment to provide evidence for the elementary steps of this reaction, we corroborate our findings by microkinetic modeling. Here, the Cbond was found to be isomerized kinetically favored toward the terminal position, before a CO molecule may be inserted. The insertion of a methoxy group (rate-determining step) was found to proceed via intermolecular attack of MeOH to the catalyst. [Copyright &y& Elsevier]

Abstract: The electronic structures, stabilities and magnetic properties of the Fe3O4(111), (110) and (001) surfaces have been computed at the level of density functional theory by including the Hubbard parameter (U) for describing the on-site Coulomb interaction of iron 3d electrons. Among the six Fe3O4(111) terminations, the Fetet1 (exposing tetrahedral coordinated iron) and Feoct2 (exposing octahedral coordinated iron) terminations are more stable and have metallic character. For the Fe3O4(110) surface, strong surface distortion has been found; the A-layer termination (exposing tetrahedral coordinated iron) has metallic character, while the B-layer termination (exposing tetrahedral and octahedral coordinated iron) has half-metal character. For the Fe3O4(001) surface, both A-layer (exposing tetrahedral coordinated iron) and B-layer (exposing octahedral coordinated iron) terminations have half-metal character. The surface stability of (111)>(001)>(110) on the basis of the computed surface energies agrees well with the experimental findings, and explains reasonably the observed diversity and complexity of the experiments. [Copyright &y& Elsevier]

Abstract: Spin-polarized density functional theory calculations have been performed to investigate carbon deposition and carbide formation on Fe(100) and Fe(110) at different carbon coverage. On Fe(100) with increasing carbon coverage, the most stable carbon adsorption configuration changes from surface carbon adsorption to surface carbon diffusion into subsurface, and surface carbon clustering is not favored thermodynamically. However, surface carbon clustering is more favored kinetically than carbon diffusion; and carbon diffusion into subsurface and surface carbon clustering become competitive. On Fe(110) with increasing surface carbon coverage, the most stable adsorption configuration changes from surface carbon adsorption to surface carbon diffusion into subsurface, and this process is favored both kinetically and thermodynamically, and surface carbon clustering is neither favored nor competitive. Surface carbon deposition might form on Fe(100), while carbide formation might be found on Fe(110). [Copyright &y& Elsevier]

Abstract: The chain growth mechanisms of Fischer–Tropsch synthesis on Fe5C2(001) were investigated at the levels of density functional theory. On the H2 and CO co-adsorbed surface, the formation of CH and CCO is the most favored initial steps. The subsequent steps of CCO coupling with C into CCCO and CCO hydrogenation into CCH2 and CHCH are competitive. Furthermore, CCH from CCH2 and CHCH dehydrogenation can couple with C to form CCCH. Since chain initiation from CO insertion obeys insertion mechanism, and chain propagation from CCH coupling obeys carbide mechanism, both mechanisms are operative and co-operative in Fischer–Tropsch synthesis. The carburized active surfaces can be regenerated and maintained by CO adsorption on the vacancy site, followed by hydrogenation into surface formyl (CHO) and successive dissociation into surface CH and O. In addition surface O can be hydrogenated into surface OH, and H2O formation from surface OH disproponation is energetically more favored than surface OH hydrogenation. [Copyright &y& Elsevier]

Abstract: The structure and energy of iron promoted γ-Al2O3 surface have been investigated in the framework of spin-polarized density functional theory using periodic slab model. It is found that the substitution of surface Al3+ by Fe3+ is thermodynamically accessible, and the promoted surfaces become metallic in nature. Full substitution of Al3+ by Fe3+ forms monolayer Fe2O3 surface. H2O adsorption leads to reconstruction of surface structures. On the basis of the computed H2O adsorption energies, the hydroxylated Fe2O3 oxide layer surface is found to be more easily dehydrated than the hydroxylated γ-Al2O3 surface. [Copyright &y& Elsevier]

Abstract: Density functional theory (DFT) calculations were employed to investigate the positions of Al in the framework of Na-MCM-22 as well as the locations and strengths of Brönsted acid sites in the corresponding H-MCM-22 analogue. Thermodynamically, the most favorable sites for locating Al are T7 and T1 sites, followed by T5, T3 and T4, while T2, T8 and T6 sites are unlikely to be occupied because of less stability. Accordingly, two types of Si(OH)Al groups, viz. isolated and H-bonded bridging OH species, were found in H-MCM-22. This finding is supported by the perfect agreement between the calculated and experimentally observed OH vibrational frequencies. The calibrated N2 and CO adsorption energies on the bridging OH sites reveal stronger Brönsted acidity of Al3–O13H–Si3 and Al4–O7H–Si4 sites than Al1–O3H–Si4 and Al3–O12H–Si3 sites. [Copyright &y& Elsevier]

Abstract: In Fischer–Tropsch synthesis (FTS), the prepared catalyst hematite (α-Fe2O3) originates from goethite (α-FeOOH) dehydration in calcinations process. The structure of α-FeOOH and its topotactic transformation into α-Fe2O3 under 300–900K have been modeled within the framework of density functional theory. Molecular dynamics simulations show that the transformation begins preferentially on the surface and the dehydration is associated with the formation of voids. The loss of H2O in α-FeOOH does not modify the morphology extremely with respect to that of the original α-FeOOH. The transformation process involves hydrogen migration with the formation of adsorbed water, followed by desorption of the water molecule. The calculated barriers for hydrogen migration (118kJ/mol) and water desorption (82kJ/mol) suggest a direct reaction path without the formation of intermediates. [Copyright &y& Elsevier]

Abstract: In order to describe the structural and energetic properties of Al-MCM-22 zeolite effectively and reasonably, ONIOM2 and ONIOM3 models as well as full B3LYP/6-31G(d) optimization on different sized clusters have been tested. On the basis of the computed bond lengths, substitution energies, proton affinities and O–H stretching frequencies for the Al1–O3H–Si4 and Al2–O9H–Si5 acid sites, three-layered ONIOM schemes (B3LYP/6-311G(d,p):HF/3-21G(d):MNDO) with 8T high-layer up to cluster sizes of 10 Å have the nearly same results as compared with those obtained from full B3LYP/6-31G(d) optimizations on 8 Å clusters. The computed O–H stretching frequencies, adsorption energy of ammonia, and Al···H1 distances agree well with the available experimental data. [Copyright &y& Elsevier]

Abstract: The direct and H-mediated dissociation of CO2 on Ni(211) were investigated at the level of density functional theory. Although formate (HCOO) formation via CO2 hydrogenation was widely reported for CO2 adsorption on metal surfaces, it is found that on Ni(211) HCOO dissociation into CHO and O is much difficult, while direct dissociation of adsorbed CO2 into CO and O is more favorable. It is also found that the degree of electron transfer from surface to adsorbed CO2 correlates with the elongation of C–O bond lengths and the reduction of the CO2 dissociation barrier. [Copyright &y& Elsevier]

Abstract: The reactivity of surface OH in CH4 reforming reactions was investigated by using density functional theory calculation. The key reaction pathway from CH4 into syngas by surface OH follows CH4 →CH→CHOH→CHO→CO, which is similar with the pathway induced by surface O in CO2 reforming of CH4 (CH4 →CH→CHO→CO). Surface OH decreases the possibility of CH dehydrogenation into surface carbon. Compared to surface O and OH, surface H can eliminate surface carbon deposition more efficiently. [Copyright &y& Elsevier]

Abstract: The adsorption of isopropanol on the clean and hydrated γ-Al2O3 (100) and (110) surfaces was investigated at the level of density functional theory. It is found that isopropanol interacts with the γ-Al2O3 surface via its −OH group. The most stable adsorption site on the (100) and (110) surfaces is Al(3) and Al(4), respectively, with the −OH group of isopropanol orientated to surface oxygen atom. The computed adsorption energies correlate well with the energy level of the surface Lewis sites. On the (100) surface with OH coverage of 8.8, Al(5) is the most stable adsorption site. On the (110) surface with OH coverages of 8.9 and 11.8, Al(2) and Al(1) are the available sites for adsorption. It is to note that water has much larger adsorption energies than isopropanol on both surfaces. [Copyright &y& Elsevier]

Abstract: Hydrogen adsorption on the Fetet1- and Feoct2-terminated Fe3O4(111) surfaces has been computed at the level of density functional theory. At 2/5 monolayer (ML), the most favored hydrogen adsorption on the Fetet1-terminated surface is homolytic and dissociative on surface O atoms, while other adsorption modes become possible at higher coverages. On the Feoct2-terminated surface at 1/3 ML, hydrogen prefers to adsorb heterolytically and dissociatively on surface Fe and O atoms, while other adsorption modes become in close energy at 2/3 and 1 ML. The Fetet1-terminated surface is more favored than the Feoct2-terminated surface for hydrogen adsorption. The adsorption mechanism has been analyzed on the basis of the calculated local density of state. [Copyright &y& Elsevier]

Abstract: The adsorption and interaction of alkali metals (Li, Na, K, Rb and Cs) with the Fetet1-terminated Fe3O4(111) surface have been computed at the level of density functional theory. At low coverage, adsorption of alkali metals on site-1 (Oa–Oc–Od) is energetically more favorable than on site-2 (Oa–Oc–Od). Li has the strongest adsorption energy, followed by K, Rb, Cs and Na. The computed net charges show that the alkali metals can donate electrons to surface Fe and O atoms in the order of Li

Abstract: Spin-polarized density functional theory has been used to characterize hydrogen adsorption on the Fe3C(100), Fe3C(001) and Fe3C(010) surfaces. It is found that hydrogen adsorbs dissociatively on the three surfaces. On the Fe3C(100) surface, the most stable surface species is CH at 1/3 or 2/3 monolayer, and CH4 at 1 monolayer; in contrast on the Fe3C(001) surface the most stable surface intermediates are 3-fold H at 1/3 monolayer, and CH at 2/3 monolayer, and CH4 at 1 monolayer. On the metallic Fe3C(010) surface, hydrogen adsorbs at 2-fold or 3-fold sites. The computed energetic order of hydrogen adsorption is Fe3C(100)>Fe3C(010)>Fe3C(001), and this differs from that of CO adsorption (Fe3C(010)>Fe3C(100)>Fe3C(001)). [Copyright &y& Elsevier]

Abstract: Density functional theory calculations have been performed on the structure and stability of Fe4C bulk and the corresponding low-index surfaces. It is found that the structure with octahedral interstitial carbon (Fe4C/oct) is more stable than that with tetrahedral interstitial carbon (Fe4C/tet). For Fe4C/oct, the most stable surface termination is the (100) surface with mixed carbon and iron (T Fe/C). For Fe4C/tet, the most stable surface termination is the dramatically reconstructed (110) surface with the newly formed T Fe/C surface layer. [Copyright &y& Elsevier]

Abstract: Spin-polarized density functional theory calculations were performed to investigate CO dissociation on clean and hydrogen precovered Fe(111) at 1/3 monolayer coverage. On clean Fe(111), the adsorbed CO first diffuses from the shallow-hollow site to the bridge-like site by elevating 0.20 eV in energy, and then dissociates into C and O atoms by overcoming a barrier of 1.53 eV. Interestingly, the CO dissociation process is accelerated in the presence of H2 via intermediate CHOads (COads + 2Hads → CHOads + Hads → CHads + Oads + Hads). This stepwise path is kinetically more favored with the lowest barrier of 1.17 eV. In contrast, the previously suggested paths, COads + 2Hads → Cads + Oads + 2Hads and COads + 2Hads → Cads + OHads + Hads, are not competitive due to higher barriers (1.76 and 1.79 eV, respectively). The activity of different low-index Fe surfaces toward CO is also compared. [Copyright &y& Elsevier]

Abstract: Density functional theory (DFT) calculations have been carried out on the adsorption of CO on the (100), (001) and (010) surfaces of Fe3C. Both (100) and (001) have surface iron and carbon atoms, while (010) has only surface iron atoms. At 1/5ML on (100), the most stable adsorption configuration has adsorbed CO at a three-fold site (three Fe atoms), followed by adsorbed surface ketenylidene at a four-fold site (three iron atoms and one carbon atom). At 1/6ML on (001), the most stable adsorption configuration has adsorbed CO at a four-fold site (four iron atoms). With increased coverage, adsorption at different sites becomes possible and close in energy. On the metallic (010) surface, both two-fold and three-fold adsorptions are close in energy. The electronic states of the most stable adsorption structures have been analyzed accordingly. [Copyright &y& Elsevier]

Abstract: Density functional theory computations have been carried out on the adsorption of NO, NO2, pyridine and pyrrole on the α-Mo2C(0001) surface for understanding the hydrodenitrogenation processes. On the Mo-terminated surface, NO decomposes into surface N and O, and NO2 dissociates into surface O and NO without any barriers, while the most stable adsorption modes of pyridine and pyrrole have π-face coordination over the three-fold molybdenum hollow sites with strongly destroyed aromatic systems. On the C-terminated surface, adsorbed surface species have been found for NO and NO2, while destroyed ring systems are found for pyridine and pyrrole. It is found that adsorption on the Mo-terminated surface is much stronger than that on the C-terminated surface. [Copyright &y& Elsevier]

Abstract: CH4 dissociation on Ni surfaces, which is important in CH4 reforming reactions, was discussed by using density functional theory. It was found that the CH x species were changed to anions after chemisorption. The site preference of CH x (x =0–3) species on Ni(111), Ni(100) and Ni(110) was located on the basis of the computed chemisorption energies. Ni(100) is the most preferred surface for CH4 dissociation, compared to Ni(110) and the widely investigated Ni(111). [Copyright &y& Elsevier]

Abstract: The structures and energetics of the chemisorbed CO2, CH x species and H as well as C2H4 on the α-Mo2C(0001) surface have been computed at the GGA-RPBE level of density functional theory. It is found that CO2 adsorbs dissociately into CO and O, in agreement with the experimental finding. The adsorbed O, CH x and H species prefer the site of three surface molybdenum atoms over a second layer carbon atom (V C site). On the basis of the calculated adsorption energies of CH x and H, the sequential dehydrogenation of CH4 and the C/C coupling reaction of CH x have been discussed. [Copyright &y& Elsevier]

Abstract: Density functional theory computations have been carried on the hydrogen adsorption mechanism on a Mo27S54 single layer cluster, which has a size (15–20Å) close to that of real catalysts. For one molecule of H2 adsorption, the most stable adsorption form (E ads =−27.2kcal/mol) is the homolytic dissociation on the S edge with the hydrogen atoms keeping away from the plane consisting of all Mo atoms, followed by the heterolytic dissociation (E ads =−26.1kcal/mol) on the intersection of S and Mo edges with the formation of Moc–H and Sc–H bonds. At high coverage with two and three H2, however, dissociated hydrogen adsorption on the Mo sites are much more favored thermodynamically than on the S sites. Moreover, the corner sites are more favored thermodynamically for hydrogen adsorption and formation of coordinatively unsaturated sites than the edge sites. In addition, the activation energy of H2 dissociation and hydrogen transfer processes have been computed to be 2.7–19.2kcal/mol, and these rather low barriers indicate the enhanced mobility of the adsorbed hydrogen on the surface. [Copyright &y& Elsevier]

Abstract: The structure and stability of the neutral cages (M12O36 and M18O54, M=Mo and W) of the Keggin and Wells-Dawson anions have been investigated at the level of density functional theory. These neutral cages can be viewed topologically as polyhedra containing triangles (f 3) and squares (f 4). The relative stability of these polyhedra is determined by the location and separation of the f 3, and the α-Keggin cage without fused triangles (N33=0) is, therefore, more stable than the β isomer with N33=3. This rule is also applicable to the Wells-Dawson cages. The structures and stabilities of these neutral cages mimic those of fullerenes within the framework of isolated pentagon rule. [Copyright &y& Elsevier]

Abstract: The structure and stability of the α/β-[AlW12O40]5− anions have been investigated with seven density functional based methods. It has been found that the relative stability of these anions are sensitive to the density functionals, and the α isomer is more stable than the β one in both gas phase and simulated aqueous medium. This conclusion has also been supported by further calculations on the relative stability of the highly charged α/β-[XW12O40] y− (X=Fe(III), Co(III), Zn(II)) anions. The BP86 incorrect assignment of the α/β-[XW12O40]5− (X=Al, Ga) stability in gas phase can be attributed to the insufficient functional. [Copyright &y& Elsevier]

Abstract: Removal of bridging sulfur from the Mo edge of a Mo20S43 cluster has been investigated at the level of density functional theory. It is found that the reductive removal of bridging sulfur is not favored energetically but becomes favorable under CO adsorption. Due to the strong adsorption, CO can help the reductive removal of surface sulfur, and in turn, the reduced Mo edge can favor and facilitate the hydrogenation process of CO. [Copyright &y& Elsevier]

Abstract: Density functional theory was employed to investigate the formation and properties of the oxygen vacancies on the rutile TiO2(110) surface. It is found that the formation of the positively charged bridging-oxygen vacancy (BOV+, 4.2eV) is the most favored one, followed by the positively charged in-plane-oxygen vacancy (POV+, 4.5eV). In contrast, the formation of the neutral bridging-oxygen and in-plane-oxygen vacancies (BOV and POV), and their dication oxygen vacancies (BOV2+ and POV2+) needs much higher energies (7.9 and 8.3 vs. 8.1 and 8.6eV), respectively. [Copyright &y& Elsevier]

High level B3LYP density functional computations identify both T2 and T4 positions in the mordenite (MOR) framework for possible Fe substitution on a cluster size of five tetrahedral centers (5T). The charge-compensating proton prefers the O5 and O10 oxygens around the T2 and T4 centers, respectively. Based on these calculations and a previous work concerning the siting of B, Al, Ga in the MOR framework, we studied the properties of the Brønsted acid sites in B, Al, Ga and Fe isomorphously substituted MOR. The calculated proton affinity, Mulliken charges on the proton and the adsorption energy of NH3 from clusters containing eight tetrahedral centers (8T) show that the acid strength increases in the order: B-MOR≪Fe-MOR

The structure and bonding of copper carbonyl complexes, [Cu(CO)n]0/+/−, have been investigated at density functional levels of theory. It was found that the bond parameters and CO bond dissociation energy are very sensitive to the size of the employed basis set. The best agreement between theory and the available experimental data has been achieved at the B3LYP level with the cc-pVTZ/TZV2P basis set. [Copyright &y& Elsevier]