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The isomerism of dimethyl 2,2′‐(7,8‐dichloro‐1H‐benzo[b][1,4]diazepine‐2,4‐(3H,5H)diylidene)diacetate (1a) and dimethyl 2,2′‐(7,8‐dichloro‐3‐methyl‐1H‐benzo[b][1,4]diazepine‐2,4‐(3H,5H)diylidene)diacetate (1b) was investigated by 1H, 13C and 15N nuclear magnetic resonance (NMR) spectroscopy. In CDCl3 solution, inversion of the diazepine ring was observed, whereas in (D6)DMSO and (D7)DMF solution, besides the ring inversion, a partial cleavage of one chelate ring appeared connected with (E/Z) isomerization about one of the exocyclic C=C bonds. Gibbs free energies (ΔG) and free activation energies (ΔG≠) were calculated based on B3PW91‐SCRF/ZVP DFT computations. Agreement between NMR data and density functional theory (DFT) computations was found. [ABSTRACT FROM AUTHOR]

Acceptorless dehydrogenation of 1‐phenylethanol to acetophenone catalyzed by OH‐functionalized N‐heterocyclic carbene Cp*Ir(NHC) complexes under base‐free condition as well as under the promotion of protic co‐solvent tBuOH were investigated using density functional theory including solvation and van der Waals dispersion corrections. The first step is the 1‐phenylethanol dehydrogenation, which is more favored via an inner‐sphere over an outer‐sphere mechanism. The second step is H2 formation from Ir–H and O–H functionalities, which is the rate‐determining step, in agreement with the observed kinetic isotopic effect. The protic co‐solvent and 1‐phenylethanol act as a shuttle for proton transfer for the formation of H2. [ABSTRACT FROM AUTHOR]

The chemoselective dehydrogenative silylation and hydrogenation of 1,3‐divinyldisiloxane by using HSiMe3 catalyzed by CpFe(CO)2Me (Cp = η5‐cyclopentadienyl) was explored by DFT computations. The active catalyst, CpFe(CO)SiMe3, was generated from a CO‐assisted pathway and HSiMe3‐initiated acetaldehyde reductive elimination. Starting from the active catalyst, the dehydrogenative silylation step of the first vinyl group was found to be the rate‐determining step, and the subsequent chemoselective hydrogenation step of the second vinyl group was discovered to be kinetically more favored. Within the reaction, the oxygen atom of 1,3‐divinyldisiloxane was not found to play a role in competitive coordination. The computed results rationalize the experimentally observed chemoselectivity. [ABSTRACT FROM AUTHOR]

The mechanism of acetonitrile and methyl benzoate catalytic hydrogenation using pincer catalysts M(H)2(CO)[NH(C2H4P iPr2)2] ( 1M) and M(H)(CO)[N(C2H4P iPr2)2] ( 2M) (M = Fe, Ru, Os) has been computed at various levels of density functional theory. The computed equilibrium between 1Fe and 2Fe agrees perfectly with the experimental observations. On the basis of the activation barriers and reaction energies, the best catalysts for acetonitrile hydrogenation are 1Fe/2Fe and 1Ru/2Ru, and the best catalysts for methyl benzoate hydrogenation are 1Ru/2Ru. The best catalysts for the dehydrogenation of benzyl alcohol are 1Ru/2Ru. It is to note that the current polarizable continuum model is not sufficient in modeling the solvation effect in the energetic properties of these catalysts as well as their catalytic properties in hydrogenation reaction, as no equilibrium could be established between 1Fe and 2Fe. Comparison with other methods and procedures has been made. © 2015 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

The reactions of [Cp*2Ti(η2-Me3SiC2SiMe3)] (Cp*=η5-pentamethylcyclopentadienyl) with various dicyano compounds were investigated. Nitrile-nitrile CC couplings result in multinuclear complexes owing to the bifunctionality of the substrates. Applying 1,3- or 1,4-dicyanobenzene led to tri- and tetranuclear complexes of the rare 1-metalla-2,5-diaza-cyclopenta-2,4-dienes. These are potential catalysts and were tested in the ring-opening polymerization of ε-caprolactone. The reaction with adiponitrile as alkyl dinitrile afforded a trinuclear 1-metalla-2,5-diaza-cyclopent-3-ene through additional protonation of the nitrogen atoms. The structure and bonding of the products were investigated by X-ray crystallography and DFT analysis to understand the molecular organization in the macrocycles. [ABSTRACT FROM AUTHOR]

Abstract: The behaviour on keto–enol tautomeric equilibration of ethyl 2-benzoyl-5-(2-furyl)-3-hydroxy-penta-2,4-dienoate (1) and ethyl 2-acetyl-3-hydroxy-5-phenyl-penta-2,4-dienoate (2) was investigated by 1H and 13C NMR spectroscopy in different solvents and BP86/TZVP density functional theory computations. The spectral assignment to enol and keto tautomers was performed with one- and two-dimensional techniques. The percentage of the keto form in the tautomeric equilibrium depends on solvents and rises by increasing solvent polarity. The enol–enol tautomerism is also discussed on the basis of the coupling constants 2 J C,OH, 3 J C,OH and 4 J H,OH, respectively. [Copyright &y& Elsevier]

The CC coupling of aryl nitriles at Group 4 metallocenes leads to unusual ring‐strained 1‐metalla‐2,5‐diaza‐cyclopenta‐2,4‐dienes. The structural, energetic, and chemical properties of these complexes are described. The reactions of these compounds towards CH3CN, H2, CO2, and HCl usually lead to the release of one nitrile and its replacement by different co‐substrates. [ABSTRACT FROM AUTHOR]

The development of earth abundant 3d metal-based catalysts continues to be an important goal of chemical research. In particular, the design of base metal complexes for reductive amination to produce primary amines remains as challenging. Here, we report the combination of cobalt and linear-triphos (bis(2-diphenylphosphinoethyl)phenylphosphine) as the molecularly-defined non-noble metal catalyst for the synthesis of linear and branched benzylic, heterocyclic and aliphatic primary amines from carbonyl compounds, gaseous ammonia and hydrogen in good to excellent yields. Noteworthy, this cobalt catalyst exhibits high selectivity and as a result the -NH2 moiety is introduced in functionalized and structurally diverse molecules. An inner-sphere mechanism on the basis of the mono-cationic [triphos-CoH]+ complex as active catalyst is proposed and supported with density functional theory computation on the doublet state potential free energy surface and H2 metathesis is found as the rate-determining step. Despite their higher abundance, 3d metal-based catalysts are less investigated than their precious metal counterparts. Here, the authors report a cobalt-triphos complex as molecularly-defined non-noble metal catalyst for the reductive amination of carbonyl compounds with gaseous ammonia and hydrogen. [ABSTRACT FROM AUTHOR]

• Coverage dependent NH 3 dissociative adsorption on metallic Mo 2 C(001) was computed. • NH 3 dissociative adsorption is exothermic and thermodynamically favorable. • NH 3 adsorption prefers top site; and the adsorption of NH and N prefers hollow site. • NH 2 adsorbs at bridge and hollow sites at low coverage; but bridge site at high coverage. • Saturation coverage of NH 3 , NH 2 , NH and N using NH 3 is 0.75, 1.0, 1.0 and 0.5 ML. Adsorption and sequential decomposition of ammonia on the metallic Mo 2 C(001) surface have been systematically computed using periodic density functional theory under the consideration of van der Waals dispersion correction (PBE-D3). It is found that NH 3 adsorption prefers the top sites from low to saturation coverage. For the adsorption of surface NH 2 , bridge and hollow sites are possible at low coverage and only bridge sites are preferred at high coverage up to saturation. The adsorption of surface NH and N prefers the hollow sites. Sequential decomposition of NH 3 into surface NH 2 , NH and N has low barrier and is highly exothermic. On the basis of surface Mo atoms, the saturation coverage of surface NH 3 , NH 2 , NH and N by using NH 3 as nitridation agent is 0.75, 1.0, 1.0 and 0.5 monolayer, respectively. These results provide the basis for the study of surface properties and catalytic reaction of nitrided Mo 2 C surfaces. The dissociative adsorption of ammonia among others metals and molybdenum nitrides has been categorized and compared. Image, graphical abstract [ABSTRACT FROM AUTHOR]

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]

Graphical abstract Highlights • Monoclinic or tetragonal ZrO 2 were tested for non-oxidative C 3 H 8 dehydrogenation. • Propene selectivity and formation rate increase with a decrease in crystallite size. • DFT calculations predict same active sites for monoclinic and tetragonal ZrO 2. • Monoclinic ZrO 2 performs superior to tetragonal ZrO 2. • The effect of the phase composition is related to the number of active sites. Abstract A series of bare ZrO 2 materials composed either of monoclinic or tetragonal phase with the size of crystallites varying between 3.7 and 43.4 nm were prepared by precipitation, hydrothermal or thermal calcination methods. The samples were characterized by XRD, BET, CO-TPR, NH 3 -TPD, electrical conductivity measurements and operando UV–vis spectroscopy. Density functional theory calculations provided molecular insights into the kind of active site and individual steps of propane dehydrogenation to propene and hydrogen. Regardless of the phase composition, two Zr cations located at an oxygen vacancy, i.e. coordinatively unsaturated Zr cations (Zr cus sites) having, nevertheless, different chemical environment in tetragonal and monoclinic ZrO 2 , were concluded to be responsible for homolytic breaking of C H bonds in propane. Monoclinic ZrO 2 showed, however, higher rate of propene formation and higher propene selectivity than ZrO 2 stabilized in the tetragonal phase. Both the activity and the selectivity to propene increased with a decrease in the size of crystallites. The effects of phase composition and crystallite size on the PDH performance were related to the ability of ZrO 2 to release lattice oxygen upon reductive catalyst treatment and thus to create Zr cus sites. The knowledge derived can be used for further optimizing PDH performance of ZrO 2 -based catalysts and also extended to other non-reducible metal oxides. [ABSTRACT FROM AUTHOR]

We systematically investigate the structural, electronic and magnetic properties, bonding analysis, as well as surface morphology of transition metal monoxides (FeO, CoO and NiO) utilizing density functional theory (DFT) with various functionals across from GGA to GGA+U and hybrid functional. Our results reveal that the screened hybrid functional (HSE) could give a reasonable description on structural and electronic properties of these strongly correlated systems when compared to experiments. Local approximation GGA functional fails to yield the accuracy band gaps. GGA+U approximation are rational when given a reasonable U, but the U which reproduce a reasonable band gap often yield a significant error in describing other properties such as lattice constant or magnetic moment. The computed Crystal Orbital Overlap Population (COOP) indicates that cubic FeO and CoO are metastable phase, while the distortion occurs to enhance stability. Based on the reliable functional, the surface morphology of FeO, CoO and NiO are predicted using Wulff construction approach. [ABSTRACT FROM AUTHOR]

The effect of Cu promoter on CH 4 formation from CO hydrogenation on Fe(100) has been investigated using spin-polarized density functional theory computations on periodic slab models. Two pathways of CH 4 formation are considered: (a) direct dissociation of CO followed by successive C hydrogenation and (b) successive hydrogenation of CO followed by deoxygenation of CH x O (x = 1–3). On the clean and Cu doped surfaces, direct dissociation of CO followed by successive C hydrogenation is more favorable kinetically and the overall CH 4 formation is endothermic. Compared with the clean surface, the Cu doped surface can suppress CH 4 formation by raising the barrier from the co-adsorbed CO + 4H. Methanol formation is unfavorable on both surfaces kinetically and thermodynamically. Reversely, methanol decomposition is favorable. It is also noted that Cu doping lowers the adsorption ability of the Fe(100) surface and therefore the adsorption energies of all species on the potential energy surfaces. [ABSTRACT FROM AUTHOR]

On the basis of spin-polarized periodic density functional theory including the latest dispersion correction (PBE-D3), the mechanisms of H 2 , O 2 , H 2 O, CO 2 , CO, CH 4 and C 2 H x dissociative adsorption on the hexagonal Mo 2 C surface have been computed. In our study we used the metallic Mo 2 C(001) surface as well as the Mo 2 C(101) surface with Mo/C = 1/1 ratio. It is found that the dissociative adsorptions of these small molecules are exothermic and have low barriers; and the Mo 2 C(001) surface has much stronger dissociative adsorption than the Mo 2 C(101) surface. In contrast to the Mo 2 C(001) surface, OH + H and O + 2H can form equilibrium on Mo 2 C(101) surface. For C 2 H x dissociative adsorption on the Mo 2 C(001) surface, C H bond dissociation is kinetically much more favorable than the C C bond dissociation, and the optimum C 2 H 6 dissociation route follows the order of C 2 H 6 → CH 3 CH 2 + H → C 2 H 4 + 2H → CH 2 CH + 3H → C 2 H 2 + 4H → C 2 H + 5H→ C 2 + 6H. Due to the very strong dissociative adsorption energies, both surfaces can be oxidized easily by using H 2 O; and high oxygen coverage can be expected. The Mo 2 C(001) surface can uptake more surface O atoms than the Mo 2 C(101) surface. These surfaces can also be carburized by using CH 4 , albeit in less extent. On the surface with co-adsorbed CO 2 + 4H; CO 2 dissociation (CO 2 → CO + O → C + 2O) is more favorable than the hydrogenation of CO 2 (CO 2 + H → HCOO or COOH) and CO (CO + H → HCO or COH). It is noted that CO 2 hydrogenation towards CH 4 formation is unlikely on the Mo 2 C(001) surface, while the effective barrier of surface C hydrogenation on the Mo 2 C(101) surface can be reduced by 2O and 2OH pre-covered surfaces. [ABSTRACT FROM AUTHOR]

Spin-polarized density functional theory computations have been performed to investigate n CO + m H 2 co-adsorption and mutual interaction on the Fe(1 1 0) and Fe(1 1 1) surfaces. It is found that CO pre-coverage affects hydrogen adsorption strongly, while H pre-coverage hardly affects CO adsorption. It is possible to have CO + H 2 co-adsorption on Fe(1 1 0), while very strong preference of CO pre-coverage on Fe(1 1 1) has been found. On Fe(1 1 1), it is also found that each CO molecule blocks on average 2H adsorption sites at all CO pre-coverage. All these findings are consistent with available experimental results. Compared with CO/H 2 ratios in gas phase, CO/H 2 surface ratios are very different and much more sensitive to temperature than pressure. Our results provide the basis for exploring the mechanisms of iron-catalyzed conversion of synthesis gas. [ABSTRACT FROM AUTHOR]

The reaction of Ni(PPh3)2Cl2 with hexahydro‐1,4‐diaza‐2,3,5,6‐tetraphosphorine in toluene leads to a trinuclear mixed valent nickel complex. Crystal structure analysis confirms three nickel atoms which are connected via two bridging chain‐like PNPPNP ligands. Moreover it indicates some remaining electron density at two central phosphorus atoms. DFT calculations on the electronic structure of the title complex suggest either a slightly delocalized unpaired electron at the relevant metal coordinated phosphorus atom or a PHPh entity. [ABSTRACT FROM AUTHOR]

In this work, the new organic–inorganichybrid compound Ph4P[(V2O3)2(PhAsO3)4⊂F] (VAsF) hasbeen prepared and characterized by single-crystal XRD and multinuclearmagnetic resonance (1H, 19F, 31P,and 51V). Redox properties and thermal stability have beeninvestigated by EPR, cyclic voltammetry, and thermal analysis in comparisonto its Ph4P[(V2O3)2(PhPO3)4⊂F] (VPF) analogue. The VAsFcluster has a lower redox potential and higher electrochemicalstability in solution, while it is thermally less stable in the solidstate. Density functional theory (DFT) calculations showed that thedifference in the redox potential is due to the different electronaffinities of VPFand VAsF. With this approachof modifying the type of the ligand of the molecular vanadium cage,we hope to enhance the utility of such compounds as building blocksfor the design of new hybrid materials with desirable properties. [ABSTRACT FROM AUTHOR]

Highlights: [•] Most, medium and least stable Fe5C2(111), (−411) and (001) surfaces are used. [•] Adsorption of H2O molecules and O atoms was calculated at high coverage. [•] Surface stability correlates with the adsorption energies of H2O and O. [•] High coverage H2O prefers hydrogen bonding instead of adsorption on iron. [•] The number of surface O atoms depends on temperature and H2O/H2 ratio. [ABSTRACT FROM AUTHOR]

Abstract: Density functional theory computations have been employed to investigate the decomposition of formic acid (HCO2H) into CO2 and hydrogen on the β-Mo2C(101) surface. The adsorption configurations and energies of the surface intermediates (HCO2H, CO2, CO, H2O, HCO2, CO2H, CHO, OH, O and H) have been systematically characterized. Among the different dissociation steps considered, our results showed the formate route (HCO2H → H + HCO2; HCO2 → H + CO2) is the minimum energy path for hydrogen formation and CO2 has very strong chemisorption. The adsorption and dissociation of formic acid on the Mo2C(101) surface have been compared with those of Pt group metals. [Copyright &y& Elsevier]

Abstract: Using the B3LYP density functional theory method we have computed the potential energy surface of the (η5-C5H5)Ir-catalyzed acetylene cyclotrimerization. The first step is the oxidative addition which forms the iridacyclopentadiene complex (2) from the bisacetylene complex (η5-C5H5)Ir(η2-HCCH)2 (1), and this is the rate-determining step. On the potential energy surface, acetylene addition to complex (2) forms the iridacyclopentadiene(acetylene) complex (3), and this step is barrier-free and highly exergonic; and complex (3) forms the benzene complex (4) via an intramolecular [4 + 2] cycloaddition. Alternatively, complex (2) and acetylene form the iridabicyclo[3.2.0]heptatriene complex (5) via an intermolecular [2 + 2] cycloaddition, and complex (5) can further isomerize into the aromatic iridacycloheptatriene complex (6a), which is a trap on the potential energy surface. This potential energy surface is qualitatively close to that for the CpRh-catalyzed reaction, but differs strongly from that for the CpCo-catalyzed reaction, which undergoes a spin crossing (or non-adiabatic) mechanism. The differences among these mechanisms as well as the relative stability of their intermediates have been compared and discussed accordingly. [Copyright &y& Elsevier]

Highlights: [•] H2O dissociative adsorption on the χ-Fe5C2(010) surface was investigated. [•] The χ-Fe5C2(010) surface has both iron and carbon regions. [•] Surface iron region is active for H2O dissociative adsorption and H2 formation. [•] Pre-adsorbed oxygen atoms play a significant role for further H2O adsorption. [•] Surface carbon region is inactive for H2O dissociative adsorption. [ABSTRACT FROM AUTHOR]

• H 2 O prefers desorption instead of dissociative adsorption on Ru(11−21) and Ru(20−21). • H 2 O prefers dissociative adsorption on O-covered Ru(11−21) and Ru(20−21) surfaces. • H 2 O dissociation capability increases in the order Ru(0001) < Ru(20−21) ˂ Ru(11−21). • CO 2 dissociative adsorption on Ru(11−21) and (20−21) is easier than that on Ru(0001). • Activity of surface O removal by H or CO growths in the order (0001)<(20−21)˂(11−21). Periodic density functional theory (RPBE) computation has been used to assess dissociative adsorption of H 2 O and CO 2 on the clean and O-pre-covered Ru(11−21) and Ru(20−21) surfaces. It is found that surface H 2 O prefers desorption on the clean Ru(11−21) and Ru(20−21) surfaces, while dissociative adsorption on O-pre-covered Ru(11−21) and Ru(20−21) surfaces, in contrary to that on O-pre-covered Ru(0001) surface. The H 2 O dissociation capability on these clean and O pre-covered Ru surfaces follows a sequence of Ru(11−21) > (20−21) > (0001). In addition, CO 2 desorption energy is comparable with the barrier of CO 2 dissociation on Ru(11−21) and Ru(20−21) (0.81 vs. 0.77 eV, 0.14 vs. 0.20 eV, respectively), indicating that CO 2 would not desorb in quantity before it occurs dissociation, which is contrary to the case on Ru(0001) (-0.32 vs. 0.23 eV). For surface O removed via H 2 O or CO 2 formation, H 2 O formation has lower effective barrier than CO 2 formation on these three Ru surfaces, in line with the experiments, and the effective barrier of H 2 O and CO 2 formation follows the increasing order of Ru(11−21) < (20−21) < (0001). [Display omitted] [ABSTRACT FROM AUTHOR]

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: The mechanism of thiophene cracking catalyzed by Brønsted acidic zeolites was computed at the level of B3LYP density functional theory. It was found that this catalytic reaction involves two major steps: (1) protonation of thiophene associated with an electrophilic aromatic substitution to another thiophene in a concerted way to form 2-(2,5-dihydrothiophen-2-yl) thiophene, and (2) Cssociation in 2,5-dihydrothiophene promoted by further protonation. The intermediate, 4-mercapto-1-(thiophen-2-yl)but-2-en-1-ylium, was found to have a CH2 group close to a Cd a SH group, in agreement with the experimental findings. A strong stabilization effect of the zeolite framework on the transition states was found by embedding the 5T cluster into the larger 34T and 56T clusters. The rate-determining step is the electrophilic aromatic substitution. [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: 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

• Coverage dependent hydrogen adsorption on Ir(111), Ir(100) and Ir(110) surfaces. • Change of adsorption site on Ir(100) from low to high coverage. • Surface dependent repulsive interaction on Ir(111). • Surface dependent attractive interaction on Ir(100) and Ir(110). • Regular line-shaped adsorption structures were found on Ir(100) and Ir(110). Hydrogen adsorption on the perfect Ir(111) as well as the metastable and unreconstructed Ir(100) and Ir(110) surfaces up to saturation coverage has been systematically computed using periodic density functional theory and ab initio atomistic thermodynamics for understanding the interaction mechanism of hydrogen on iridium surfaces. On the Ir(111) surface including van der Waals dispersion, hydrogen adsorption prefers the threefold hollow sites at low coverage and the top sites at high coverage; in agreement with the experiments (Phys. Rev. B 60 (1999) 14016). The computed adsorption energy and desorption temperature of hydrogen agree with the experiments [−0.57 (fcc-3H) and −0.53 (hcp-3H) vs. −0.55 eV; 180 and 325 K vs. 190 and 310 K, respectively]. On the Ir (100) surface, the bridge adsorption sites are preferred in the whole coverage range, in agreement with the LEED pattern (Phys. Rev. B 73 (2006) 75430), however, adsorption energy and desorption temperature are slightly overestimated by including van der Waals dispersion (−1.50 vs. −1.02 ± 0.15 eV; 470 vs. 425 – 389 K). On the Ir(110) surface, short-bridge sites are preferred at low coverage and the top sites become dominant at high coverage, and the calculated desorption temperatures are close to experiments by including van der Waals dispersion (210 and 365 K vs. 220 and 375 K). At low coverage, the different configurations of hydrogen adsorption on the Ir(111) have the similar energies, indicating their negligible repulsive interaction, while the Ir(100) and Ir(110) surfaces prefer regular line-shape adsorption configurations due to attractive interaction, and such adsorption configurations have not been observed experimentally. Our results show that differences in adsorption configurations and energies are associated with their differences in surface structures, and in turn explain the need of different methods in computing the adsorption properties on different surfaces. Such surface-dependent properties should also be possible on other metal surfaces. Image, graphical abstract [ABSTRACT FROM AUTHOR]

• Coverage-dependent CO hydrogenation was computed and compared. • At 0.25 reasonable coverage CO dissociation prefers H-assisted path leading to CH formation. • Apparent barrier of methanation is in close agreement with experimental value. • Ketene is the intermediate from CH 2 and CO coupling for the first C-C bond formation. • CH 3 C is the homologue of CH and starts the cycle for chain propagation. For the first time the full catalytic cycle of CO activation, methanation and first C-C bond formation on Fe(110) at high coverage [0.25 ML, p (2 × 2)] have been computed by density functional theory. Under thermodynamic equilibrium, H-assisted CHO formation and CHO dissociation into CH+O are preferred thermodynamically and kinetically. Then CH can be transformed into methane via successive hydrogenation; and the first C-C bond can be formed by CH 2 and CO coupling resulting in ketene (CH 2 CO), which can be hydrogenated to acetyl (CH 3 CO). The next C-O dissociation of CH 3 CO results in CH 3 C (higher homologue CH), and this starts C-C chain growth and catalytic cycle. Both methanation and chain growth have the same rate-determining step as CHO dissociation. The computed apparent barrier of methanation is much close to experimental value. These high coverage results clearly explain the experimentally observed formation of methane as well as high hydrocarbons of synthesis gas conversion on metallic Fe surface. The computed vibrational frequencies of the proposed surface intermediates agree with the experimental data. This high coverage strategy should be applicable to other heterogeneous catalytic reactions having coverage preferences. Image, graphical abstract [ABSTRACT FROM AUTHOR]