We have studied the effect of CH4 dissociation and partial oxidation on carbon deposition resistance on oxygen-defective anatase TiO2 supported Rh (Rh4/Ana-Ov) and rutile TiO2 supported Rh (Rh4/Rut-Ov) by the density functional theory. We computed the adsorption structure of CHx species, and the adsorption of CHx species on Rh4/Rut-Ov was stronger than that on Rh4/Ana-Ov. On the Rh4/Ana-Ov surface, the activation energy barrier of C–H bond cleavage involved in methane decomposition was higher than that on Rh4/Rut-Ov, which means the Rh4/Ana-Ov was favored to carbon deposition resistance. Additionally, the dominant process of methane partial oxidation was CH2*+O* → CH2O*, where the energy barrier on Rh4/Ana-Ov is lower relative to Rh4/Rut-Ov. This implies that the oxidation reaction was also favorable to the carbon deposition resistance on Rh4/Ana-Ov. As the strong carbon deposition resistance effect on Rh4/Ana-Ov, a high activity for syngas formation can be expected. The energetic span model analysis showed that the apparent activation energy was beneficial to the partial oxidation of methane on Rh4/Ana-Ov compared to that of Rh4/Rut-Ov. Moreover, the selectivity of CO was high and up to 90% by using the microkinetic model analysis, which was consistent with the experimental results. The present work may help people to design an efficient catalysts for methane partial oxidation in which there is a strong interaction with support in order to reduce the carbon deposition.

Spin-polarized density functional theory computations have been used to investigate the CO dissociation mechanisms and the different catalytic activities of the reaction on Fe(100) surfaces with different Pd coverages. CO can dissociate on Pd/Fe surfaces via three different mechanisms: direct and H-assisted mechanisms via HCO intermediate or COH intermediate. In our calculation, it was found that the activation barriers of direct CO and COH dissociation mechanisms on pure and Pd-doped Fe(100) surfaces were higher than that of the HCO dissociation mechanism. Besides, energy barriers for the identical reaction pathway on Fe-rich Fe(100) surfaces were lower than those on Pd-rich Fe(100) surfaces, namely, CO dissociation mainly occurs via the HCO intermediate pathway and the catalytic activity becomes lower with Pd coverage increasing toward CO dissociation in both direct CO and H-assisted CO dissociation mechanisms. As a result, CO dissociation mainly occurs on Fe-rich Pd/Fe surfaces, leading to the formation of CHx, and Pd-rich Pd/Fe surfaces can stabilize CO, which may afford the high selectivity to oxygenate. The bimetallic catalysts will provide two different active sites that are synergetic for the formation of higher alcohols. Moreover, the difference between Pd-doped and Cu-doped Fe(100) systems was compared and analyzed based on the d-band model, and it was found that the d-bandwidth of Cu/Fe(100) was more narrow compared to that of Pd/Fe(100); this was agreement with the calculation results that the energy barrier for C–O bond scission on Cu/Fe(100) was lower than that on Pd/Fe(100). We predicted that methane content decreases and methanol content increases with Pd coverage increases on Pd/Fe(100), and the selectivity of methanol on Pd/Fe(100) is higher than that on Cu/Fe(100). Importantly, a typical “ volcano curve” between ethanol synthesis and the HCO dissociation barrier was gained, in which the selectivity for the ethanol synthesis is highest on the Fe2Cu2/Fe(100) system among these studied bimetallic model catalysts due to its moderate catalytic activity for HCO dissociation.

Single-crystalline Pd nanocrystals enclosed by {111} or {100} facets with controllable sizes were synthesized and originally employed as catalysts in the aerobic oxidation of 5-hydroxymethyl-2-furfural (HMF). The experimental results indicated that the particle size and exposed facet of Pd nanocrystals could obviously influence their catalytic performance. The size-dependent effect of Pd nanocrystals in this reaction could only be derived from the different Pd dispersions. Therefore, the facet effect of Pd nanocrystals was first investigated in this work through experimental and theoretical approaches. It was found that Pd-NOs enclosed by {111} facets were more efficient than Pd-NCs enclosed by {100} facets for the aerobic oxidation of HMF, especially for the oxidation step from 5-hydroxymethyl-2-furancarboxylic acid (HMFCA) toward 5-formyl-2-furancarboxylic acid (FFCA). The TOF value of Pd-NOs(6 nm) was 2.6 times as high as that of Pd-NCs(7 nm) and 5.2 times higher than that of commercial Pd/C catalyst for HMF oxidation. Through density functional theory (DFT) calculations, the notably enhanced catalytic performance of Pd-NOs could be mainly attributed to the lower energy barrier in the alcohol oxidation step (from HMFCA to FFCA) and higher selectivity for O2 hydrogenation to produce peroxide.Keywords: 5-hydroxymethyl-2-furfural; aerobic oxidation; facet effect; single-crystalline Pd; size-dependent effect;

C–C and C–O bond scission are important reactions that have been extensively studied experimentally; however, the decomposition mechanism for long-chain alkanols is still not clear. In the present study, density functional theory calculations were performed to study the reaction mechanisms of C–O and C–C cleavage in 1-hexadecanol on Pt and Ru. The adsorption mechanisms and the reaction cycles for 1-hexadecanol (1-C16H34O) decomposition were clarified in this study. The mechanisms include dehydrogenation steps and C–O and C–C cleavage steps. The present calculation results show that the main mechanism of 1-hexadecanol decomposition on Pt(111) is C14H29CH2CH2OH → C14H29CH2CHOH → C14H29CH2COH → C14H29CH2C → C14H29CH2CH → C14H29CH2CH2 → C14H29CH2CH3, and the C–O bond cleavage mechanism is favored over that of C–C bond cleavage. The major final product is n-hexadecane (C14H29CH2CH3), and the C–O cleavage and the formation of the C14H29CH2CH2 species are the rate-controlling steps. However, on Ru the mechanism is C14H29CH2CH2OH → C14H29CH2CH2O → C14H29CH2CHO → C14H29CH2CO → C14H29CHCO → C14H29CH + CO → C14H29CH2 → C14H29CH3, and the dominant product is n-pentadecane (C14H29CH3). The rate-controlling steps are the dehydrogenation of C14H29CH2CO into the C14H29CHCO species and the hydrogenation of C14H29CH2 into C14H29CH3 species. The resulting CO is converted into CH4 according to CO → HCO → H2CO → CH2 → CH3 → CH4. The rate-limiting step is the formation of HCO. These calculation results clearly show that the C–O bond scission mechanism is favored over the C–C bond scission mechanism on Pt, whereas the opposite situation occurs on Ru; namely, this reaction is strongly metal dependent. The different mechanisms originate from different initial cleavage channels, in which Cα–H scission is preferred for 1-hexadecanol on Pt, whereas O–H scission is the dominant cleavage on Ru. Moreover, it was found that the selectivity and reactivity could be modified by modifying the experimental conditions such as H2 pressure. Confirming the mechanisms of C–C and C–O cleavage will aid the modification of experimental conditions to obtain high selectivity products. The present calculation results can be extended to other metals, such as Ni, bimetallic alloys, such as Ni/Pt(111), or other alkanol reaction systems.

•The ER and LH mechanisms for acetylene hydrochlorination catalyzed by gold catalysts are studied.•Tri-coordinated gold chloride shows high activity in catalyzing acetylene hydrochlorination.•Cl-transfer is the key step in the LH mechanism to form a new vacant site to adsorb HCl strongly.Reaction mechanisms of acetylene hydrochlorination catalyzed by AuCl3/C catalysts were investigated by density functional theory calculations. Tri-coordinated gold chloride with a vacant site shows high activity in adsorbing HCl and C2H2. Mechanisms in the first adsorption of HCl and C2H2 on gold were found to be the Eley-Rideal (ER) and the Langmuir-Hinshelwood (LH) mechanisms, respectively. The transfer of Cl atom of AuCl3 to acetylene is the key step in the LH mechanism, which could form new vacant site to adsorb HCl effectively. Tri-coordinated gold was formed by removing Cl atom through addition reaction of acetylene in the induction period.

Mo/ZSM-5-catalyzed methane conversion into aromatic hydrocarbons is an important reaction to produce ethylene and benzene, but the detailed reaction mechanism has not been investigated due to its high complexity. In the present study, density functional theory combined with a periodic model was used to investigate the reaction mechanism of direct methane conversion into aromatic hydrocarbons catalyzed by Mo/ZSM-5. The calculation results show that the active phase for Mo is Mo4C2 instead of MoOx. The whole reaction processes processed via the following steps: the C–H bond in methane was first activated by Mo4C2 with an energy barrier of 1.01 eV and then converted into ethylene species via the coupling of two CH3 species as well as two successive dehydrogenation steps (2CH3 → C2H6 → C2H4 + 2H). The rate-controlling step for the processes to form ethylene is the coupling of two methyl species with a barrier of 1.22 eV. The produced ethylene species then react with each other to produce C6H8via the reaction of 3C2H4 → C3H8 + 2H2, and molecular benzene is formed by successive dehydrogenation of C6H8. The rate-limiting step for benzene formation from ethylene is the cyclization step of chain C6H8 with an energy barrier of 1.21 eV. Additionally, molecular propane (C3H8) is formed by the reaction of C2H4 + CH4 → C3H8, and the controlling step C3H7 + H → C3H8 has a barrier of 1.46 eV. Molecular C10H12 is produced via coupling of C6H8 and C2H4, where the limiting step is the dehydrogenation step of C8H12 with an energy barrier of 1.44 eV. Our present calculation results indicate that the selectivity of benzene was the largest among the possible products, that is, C2H4, C3H6, C6H6 and C10H12, based on the corresponding controlling step barrier. Importantly, the rate-controlling step for the whole reaction process from methane to benzene is the dissociative adsorption of methane (CH4 → CH3 + H) with an energy barrier of 1.83 eV when considering entropy contribution. The present study may help people design a good catalyst for the formation of benzene from methane; in other words, the catalyst should have a good ability to activate the C–H bond of molecular methane.

Steam-methane reforming is a method of converting natural gas to syngas, and the additive K could affect the activity of steam-methane reforming on Ni catalyst supported by Al2O3. In addition, K could release carbon deposition. In the present work, density functional theory calculations were performed to study the reaction mechanisms and catalytic activity of steam-methane reforming on clean and K pre-adsorbed Ni4 clusters supported by Al2O3. Adsorption situations and the reaction cycles for steam-methane reforming reactions on clean and K pre-adsorbed Ni4-Al2O3 clusters were clarified. The rate-limiting step is the dissociative adsorption of molecular methane. K will promote steam-methane reforming through donating electron density and enhancing the activity of Ni by enhancing the overlapping of the orbitals of Ni and C. As a result, the barriers of C–H cleavage in the first two steps of CH4 dissociation on K pre-adsorbed Ni4 clusters are lower than that on clean clusters and thus retain the activity of steam-methane reforming. On the contrary, the barriers of C–H cleavage in the last two steps of CH4 dissociation on K pre-adsorbed Ni4/Al2O3 are higher than that on clean Ni4/Al2O3 and thus K will relieve the carbon deposition, which is in good agreement with the experimental results.

The mechanism of Rh2(R-TPCP)4-catalyzed [3 + 2]-dipolar cycloadditions between vinyldiazoacetate and nitrone to form 2,5-dihydroisoxazole has been studied by ONIOM methodology calculations including density functional theory and semi-empirical PM6 theory. This mechanism begins with carbenoid formation catalyzed by a rhodium catalyst, followed by vinylogous addition/cyclization of an iminium to construct a five-membered ring isoxazolidines, and followed by the functionalization processes of 1,3-hydride abstraction/proton transfer to generate 2,5-dihydroisoxazoles. The calculated results indicate a distinct stepwise fashion of this [3 + 2]-cycloaddition because of the extremely transient intermediate that emerged in the vinylogous reaction, and the cyclization of iminium addition is deemed to be the enantio-controlling step. According to analysis of thermodynamic information, the process of protonation has the highest energy barrier in this catalytic cycle and is determined as the rate-controlling step. A higher enantioselective formation of (R)-2,5-dihydroisoxazole derived from the reaction between aryl nitrone and s-trans vinylcarbenoid is evaluated. What's more, we kinetically analyze the enantioselectivity of this complete catalytic cycle by the AUTOF program and provide the reactivity trends with an activation strain model.

In this work, seven novel phases of phosphorene were predicted to be existent by first-principles calculations, including six kinds of enantiomers corresponding to three kinds of structures with chirality. It is the first time to introduce chirality into two-dimensional (2D) phosphorus. The Poisson’s ratios have been investigated and show normal behavior, rather than the negative one of monolayer or bulk black phosphorus, due to the structures being non-puckered. Phase transformations of these enantiomers have been studied, revealing that there exists the possibility of transformations between them because of the energy barriers being low, which opens doors to possible applications in shape memory devices. This work may inspire new ideas of developing novel applications based on 2D phosphorus nanomaterials.

•Three kinds of BN 2-dimensional material are predicted and proved their possibility of existence.•A method of doping organic molecules to engineer the band gap of these three structures.•It is double side doping different molecules that performs efficiency in band engineering.We investigated the existence possibility of homo-elemental bond BN porous nanosheet (homo-pBN) and homo-elemental bonding inorganic graphenylene (hIGP) by first principle simulation calculation and tuned down their band gap by the means of doping organic molecules. We studied the structure and charge population of BN porous nanosheet with homo-elemental N–N bond (pBNhN), BN porous nanosheet with homo-elemental B–B bond (pBNhB) and hIGP. Meanwhile, calculations show that they transferred charge to (from) organic molecules. The donor (TTF) and the acceptor (TCNQ) make BN structure transfer to n-type semiconductor and p-type semiconductor, respectively. Furthermore, band gap is significantly reduced when the donor and the acceptor are simultaneously adopted as a couple. This investigation may inspire the possibility of developing electronic material made by BN structure of 2-dimensional group.

Periodic density functional theory(DFT) calculations are presented to describe the adsorption and decomposition of CH3OH on Ru(0001) surfaces with different coverages, including p(3×2), p(2×2), and p(2×1) unit cells, corresponding to monolayer(ML) coverages of 1/6, 1/4, and 1/2, respectively. The geometries and energies of all species involved in methanol dissociation were analyzed, and the initial decomposition reactions of methanol and the subsequent dehydrogenations reactions of CH3O and CH2OH were all computed at 1/2, 1/4, and 1/6 ML coverage on the Ru(0001) surface. The results show that coverage exerts some effects on the stable adsorption of CH3O, CH2OH, and CH3, that is, the lower the coverage, the stronger the adsorption. Coverage also exerts effects on the initial decomposition of methanol. C—H bond breakage is favored at 1/2 ML, whereas C—H and O—H bond cleavages are preferred at 1/4 and 1/6 ML on the Ru(0001) surface, respectively. At 1/4 ML coverage on the Ru(0001) surface, the overall reaction mechanism can be written as 9CH3OH→3CH3O+6CH2OH+9H→6CH2O+3CHOH+18H→ 7CHO+COH+CH+OH+26H→8CO+C+O+36H.

In the present work, the density functional theory calculations analysis are performed to study the reaction mechanisms and catalytic activity of ethanol reactions over Co0, Co2+, and Co3+ sites. Adsorption situations and the reaction cycles for ethanol reactions on cobalt catalysts were clarified. The mechanisms include the dehydrogenation steps of ethanol and the C–C cleavage step. The present calculation results show that the mechanism of ethanol reaction on Co0 site is CH3CH2OH → CH3CH2O → CH3CHO → CH3CO → CH3+CO, and the final products are CO and H2. H2 is formed by the combination of adsorbed H species. On Co2+ site, the mechanism is CH3CH2OH → CH3CH2O → CH3CHO, and the main final product is CH3CHO species. On Co3+ site, the mechanism is CH3CH2OH → CH3CH2O → CH3CHO → CH2CHO → CH2CO → CHCO → CCO → COCO → CO → CO2, and the final products are CO2 and H2O. The rate-limiting step on Co0, Co2+, and Co3+ sites is the form of CH3CHO species. The possible reasons for the different catalytic activities may be the following two facts: First, Co3+ sites density in Co3O4 (110)-A is larger than that of Co2+ and tends to break the C–C bond to produce CO; second, Co3+ binds more oxygen atoms that the further oxidation of ethanol requires, which leads to the full oxidation of ethanol to CO2 on Co3+ sites. The present result may help people to design an ESR (ethanol stream reaction) catalyst by controlling its oxidation state, and the catalyst with modest oxidation state is benefit for the H2 formation. The proper catalyst should own the ability to break C–C to form CO but avoid the full oxidation of CO into CO2 which is needed to react with H2O in the water–gas shift reaction generating CO2 and H2.

In the present work, the microkinetic model analysis is performed to study the reaction mechanisms and catalytic activity of ethanol reactions over Co0, Co2+, and Co3+ sites. On the Co0 site, it has been reported that the mechanism of ethanol reaction is CH3CH2OH → CH3CH2O → CH3CHO → CH3CO → CH3 + CO, and the final products are CO and H2. H2 is formed by the combination of adsorbed H species. The microkinetic simulation shows that the elementary steps of the dehydrogenation of CH3CH2O species into CH3CHO, C–C cleavage in CH3CO, and desorption of CO dominate the rate of CO formation as the rate-controlling steps. The elementary steps of desorption of CH3CHO and the C–C cleavage in CH3CO species have the main impact on the selectivity as the selectivity-controlling steps. On the Co2+ site, the mechanism was reported to be CH3CH2OH → CH3CH2O → CH3CHO, and the main final product is CH3CHO. The microkinetic simulation demonstrates that the rate-controlling step is desorption of CH3CHO. The selectivity-controlling steps are desorption of CH3CHO and the dehydrogenation in CH3CHO. On the Co3+ site, the mechanism has been examined, CH3CH2OH → CH3CH2O → CH3CHO→ CH2CHO→ CH2CO → CHCO → CCO → COCO → CO → CO2, and the final products are CO2 and H2O. The corresponding rate-controlling step and selectivity-controlling step on the Co3+ site is the step of dehydrogenation in CH3CH2O species into CH3CHO species. The present result may help people to modify the experiment condition as the pressure, temperature, and catalyst to get the target product as CH3CHO, CO, and CO2 with high selectivity and reactivity.

Catalytic reaction of propylene partial oxidation by copper oxide has been considered as an environmentally friendly route, and the selective oxidation of propylene to acrolein and propylene oxide is of significance. Herein, the catalytic mechanism of metallic oxide CuO (111) and CuO (100) catalysts for propylene partial oxidation has been investigated by us via density functional theory calculations with a Hubbard U correction; concomitant microkinetic simulations are carried out to discuss the catalytic activity. We have reported two parallel reaction pathways on both surfaces in detail: dehydrogenation and epoxidation. The transition states and energy profiles are calculated for the formation of intermediates as well as products. On the two surfaces, acrolein is obtained by two H-stripping reactions in the dehydrogenation process. Furthermore, in the epoxidation reaction, propylene oxide and propanal can be created through one propylene oxametallacycle intermediate, competing with the pathway that propylene oxide and acetone can be produced through the other propylene oxametallacycle intermediate. In our calculation, it is found that the activation barriers of propanal and acetone generated from different intermediates on (111) surface are too high, and acrolein is the main product. Besides, energy barriers for the identical reaction pathway on (100) facet are lower than those on (111) facet; microkinetic simulations also show that the turnover frequency of acrolein at the same temperature on (100) surface is larger than that on (111) surface. Moreover, it is found that not only acroline can be formed on (100) facet but also propylene oxide can be formed, which is different from the case of (111) facet where acroline is the only product. All of these results indicate that the catalytic activity on (100) surface is higher toward propylene partial oxidation than that of (111) surface. The reason why (100) facet is more active than (111) has been analyzed by the density of state calculation, and it is also found that the states of the d orbitals of Cu atoms in (100) facet are closer to the Fermi level compared to those of the Cu site in (111) facet.

It is essential to understand and control the O–H bond cleavage on metal surfaces with pre-adsorbed oxygen atoms in heterogeneous catalytic processes. The adsorption and dissociation of water on clean and oxygen-pre-adsorbed copper surfaces, including Cu(111), Cu(110), Cu(100), Cu(210), Cu(211), Cu(310) and Cu(110)-(1 × 2), as well as Cu-ad-row and Cu-ad-atom, have been investigated by the density functional theory-generalized gradient approximation (DFT-GGA) method. The calculation results indicate that the presence of oxygen species significantly promotes the water dissociation. It is found that the promotion effect depends both on the adsorption energy of the pre-adsorbed oxygen and the distance between the pre-adsorbed oxygen and the stripped hydrogen in water: the more strongly the oxygen atom binds to the metal surface, the less the promotion effect it has on the water O–H bond cleavage; the shorter the distance between pre-adsorbed oxygen and hydrogen in water, the greater is the promotion effect. Based on electronic analysis, physical origin of the promotion effect can be attributed to the strong interaction of acid–base pair sites on oxygen–metal systems.

Density functional theory was used to investigate the reaction mechanisms of ethylene hydrogenation on MgO(100)- and γ-Al2O3(110)-supported carbon-containing Ir4 clusters. The cluster supported on γ-Al2O3(110) is more active than that on MgO(100), which is consistent with experimental observations. The present calculations show that the binding energies of reactants on the carbon-containing Ir4 cluster are weaker on the γ-Al2O3 supported catalysts compared to the MgO supported Ir cluster. This relatively weak adsorption energy of ethylene on the γ-Al2O3 surface means that ethylene desorption is easier, hence a higher catalytic activity is achieved. To gain further understanding, the energy decomposition method and micro-kinetic analysis are also introduced.

Single atom catalysts usually show unique catalytic activity and the physical nature is not clear. In the present work, density functional theory calculations are presented for adsorption and dissociation of CH4 on clean and oxygen atom pre-adsorbed Rh metal surfaces with different coordinate numbers such as (111), (100), (110), (211), kink, ad-row (add two atoms on a p(2 × 2)-111 unit cell) and ad-atom (add one atom on a p(2 × 2)-111 unit cell). The present calculation results show that the pre-adsorbed oxygen atom inhibits the methane dehydrogenation on Rh surfaces in general except on the ad-atom model where it has no effect, thus resulting in the possibility of the partial oxidation of methane to produce syngas (the mixture of CO and H2) on Rh ad-atom catalysts. Having been analyzed by the barrier decomposition method, it was found that the presence of an oxygen atom usually reduces the adsorption energy of dissociated fragments and increases the interaction between the dissociated fragments, both of which lead to an increase of the reaction barrier. Moreover, the electronic analysis indicated that the oxygen effect can be attributed to the strong interaction of acid–base pair sites on oxygen–metal systems, and a strong acid–base interaction related to the low dehydrogenation barrier.

The decomposition mechanisms of methylamine on a Pt(100) surface have been systematically investigated using density functional theory calculations. The most stable configurations and the corresponding adsorption energies for all the possible species involved were obtained, and the decomposition network was mapped out based on the energy barriers of the possible elementary reactions involved in methylamine decomposition. Desorption is preferred for adsorbing methylamine and hydrogen, whereas for the other species decomposition is more favorable. The most likely pathway for methylamine decomposition on Pt(100) is H3CNH2 → H2CNH2 + H → H2CNH + 2H → HCNH + 3H → HCN + 4H → HCN + 5H → CN + 5/2H2(g), which is different from the reaction mechanism on Pt(111), which is H3CNH2 → H3CNH → H3CN → H2CN → HCN.

In this paper, the mechanism of chiral rhodium-catalyzed [4+3] cycloaddition between a vinylcarbenoid and a diene to form cycloheptadiene has been studied using a two-layer ONIOM methodology consisting of density functional theory and semiempirical PM6. The mechanism involves the formation of vinylcarbenoid via nitrogen extrusion, cyclopropanation to form a divinylcyclopropane through removal of the catalyst, followed by Cope rearrangement of the resulting cis-divinylcyclopropane to form a cycloheptadiene. In this study calculations were carried out on tandem reactions of vinyldiazoacetate and siloxyvinyldiazoacetate with the consideration of geometric isomerism. Through the analysis of thermodynamics and kinetics the Cope rearrangement involving a boat transition state was determined as the rate-controlling step. The computational results indicated that siloxy substituted vinylcarbenoid displays a higher energy barrier and obtains reasonably higher enantioselectivity than for cyclopropanation of unsubstituted vinylcarbenoid, thus it has a critical influence on the favored product of ring extension and the chemical activity. Besides, the geometric isomerism of the substrates and the trapping approach were predicted to have full control over the stereogenic center of the final product rather than the enantioselectivity. Moreover, a desired relationship between the properties of the substrates and reaction energies has been established to understand the reactivity trend by activation strain model (ASM). Finally, an energy span model and AUTOF program were used to create a link between the catalytic cycles and the properties of the substrates.

The initial dissociative adsorption step of the 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD) molecule on the surfaces of MgO, CaO, and CuO has been studied by density functional theory (DFT) using periodic slab models. It is found that the 2,3,7,8-TCDD molecule undergoes a similar dissociative adsorption step during the decomposition over the three metal oxide surfaces. The adsorption configuration of 2,3,7,8-TCDD first converts from a parallel mode into a vertical one, then a nucleophilic substitution process takes place, where the surface oxygen atom attacks the aromatic carbon to form a surface phenolate with the chlorine atom moving to the top of the nearest surface metal atom. The calculated apparent activation energy of the dissociation increases in the order of CuO < CaO < MgO. The reaction heat is −0.67 eV, −0.75 eV, and 0.45 eV for CuO, CaO, and MgO, respectively, suggesting the thermodynamic tendency of MgO < CuO < CaO, which parallels the trend of the nucleophilicity of surface oxygen atoms. This study suggests that metal oxides with more nucleophilic and less tightly-bonded surface oxygen atoms might be more promising for the decomposition of polychlorinated dibenzo-p-dioxins and dibenzofurans.

It is well known that the addition of Ag into Pd can promote the selectivity of acetylene hydrogenation to ethylene, and early theoretical studies focus on ideal single crystal model catalysts, so it is worth studying relatively realistic catalyst models, such as metal oxide supported PdAg systems. In this work, the reaction mechanisms for acetylene selective hydrogenation on the anatase TiO2(101) supported PdaAgb (a + b = 4) cluster are studied by density functional theory calculations with a Hubbard U correction. The results show that Ag addition to the Pd4 cluster reduces the interaction between the PdAg cluster and the support, and the possible reason is that the amount of electron transfer from the TiO2 support to the PdAg cluster decreases with increasing number of Ag atoms. Consequently the adsorption energies of acetylene and ethylene would become smaller on the anatase supported PdAg cluster as compared to that on the anatase supported Pd4 cluster, and this may help to enhance the selectivity of ethylene formation. Moreover, the reaction kinetics study of acetylene hydrogenation on anatase TiO2(101) supported PdAg cluster shows that the activation energy of the hydrogenation step is higher on the PdAg cluster than that on the pure Pd4 cluster, and thus reduces its catalytic activity. Importantly, the present calculation results suggested that the selectivity of ethylene formation, which is defined as the energy difference between the adsorption energy of ethylene and the barrier for its further hydrogenation, varies with the ratio of Pd/Ag in the PdAg cluster: the Pd3Ag system shows relatively low selectivity compared to that of the pure Pd4 cluster, whereas Pd2Ag2/PdAg3 displays higher selectivity than that of the pure Pd4 cluster. Furthermore, our present results demonstrated that the anatase support plays a key role in the acetylene hydrogenation processes: on one hand, it reduces the reaction activity of acetylene hydrogenation processes compared to the Pd2Ag2/Pd(111) and Pd2Ag2 clusters; on the other hand, it enhances the selectivity of ethylene due to its lower desorption energy. It was also found that the carbon species inside the Pd2Ag2 cluster has little effect on the catalytic selectivity towards ethylene formation, whereas the hydrogenation catalytic activity is enhanced significantly. Finally the role of the Pd2Ag2–anatase interface on the catalytic properties of acetylene hydrogenation was studied, and it was found that the interface can increase the activity of acetylene hydrogenation but the selectivity is not improved.

Density functional theory calculations are presented for adsorption and dissociation of NH3, H2O, CH3OH, H2S and C2H4 on clean and oxygen atom pre-adsorbed metal surfaces (Cu, Ag, Au, Ni, Pd, Pt, Rh, Ru, Os and Ir). The calculation results indicated that the oxygen-promotion effect depends both on the metallic activity and the character of the X–H bond. On the one hand, for a given reaction on a series metals, a good linear correlation was found between the energy barrier difference of X–H bond breaking on clean and oxygen-covered metals and the binding strength of oxygen on metals, namely an oxygen-promotion effect was favorable to the less active metals but unfavorable to the more active metals. On the other hand, for a series of X–H bond breaking reactions on a given metal, it was found that the promotion effect follows the trend of O–H > N–H > C–H, that is, the O–H bond is most promoted by the oxygen atom. The possible reason is the O–H bond forms the strongest hydrogen bond in the transition state among the X–H bonds investigated in this work. Additionally, it was found that the oxygen coverage has little effect on the X–H bond scission.

Using ionic liquids as controlling agents is known to effectively affect the morphologies of TiO2 crystals. To obtain a profound understanding of this observation, density functional theory calculations with inclusion of Grimme treatment of the dispersion forces (DFT+D) have been performed to study a typical ionic liquid 1-ethyl-3-methylimidazolium bromide ([Emim]Br) adsorption on the low-index TiO2 facets, and the equilibrium crystal shape of TiO2 has been predicted using Wulff’s rule. [Emim]Br is found to adsorb most strongly on (110) for rutile and (100) for anatase. The gap of surface energy shows an obvious increase after [Emim]Br adsorption, especially, between (101) and (001) for anatase and also between (110) and (001) for rutile. This gap variation results in increasing the (100) facet exposure of anatase, and an increase in the length-to-diameter ratio of rutile nanocrystals, which is verified by our experiments. This study is meaningful to gain further understanding of how ionic liquids achieve shape-controlled nanocrystals synthesis by turning surface chemistry, which will push a valuable step toward the ultimate goal, controlling synthesis of inorganic nanomaterials.

•DFT calculations were performed to study CO hydrogenation to methane on Mo2C.•Reaction mechanism is CO → HCO → H2CO → H2COH → CH2 → CH3 → CH4 on Mo2C.•CH3 + H → CH4 is the rate-determining step.•Barrier of CH3 + H → CH4 on fcc-Mo2C (100) is lower than on hcp-Mo2C (101).The reaction mechanisms for the CO hydrogenation to produce CH4 on both fcc-Mo2C (100) and hcp-Mo2C (101) surfaces are investigated using density functional theory calculations with the periodic slab model. Through systematic calculations for the mechanisms of the CO hydrogenation on the two surfaces, we found that the reaction mechanisms are the same on both fcc and hcp Mo2C catalysts, that is, CO → HCO → H2CO → H2COH → CH2 → CH3 → CH4. The activation energy of the rate-determining step (CH3 + H → CH4) on fcc-Mo2C (100) (0.84 eV) is lower than that on hcp-Mo2C (101) (1.20 eV), and that is why catalytic activity of fcc-Mo2C is higher than hcp-Mo2C for CO hydrogenation. Our calculated results are consistent with the experimental observations. The activity difference of these two surfaces mainly comes from the co-adsorption energy difference between initial state (IS) and transition state (TS), that is, the co-adsorption energy difference between IS and TS is − 0.04 eV on fcc Mo2C (100), while it is as high as 0.68 eV on hcp Mo2C (101), and thus leading to the lower activation barrier for the reaction of CH3 + H → CH4 on fcc-Mo2C (100) compared to that of hcp-Mo2C (101).

•CO oxidation occurs via the L-H mechanism at low oxygen coverage.•O oxidation occurs via the E-R mechanism at high oxygen coverage.•Barriers of CO oxidation follow the order of Pt(111) > Pt/Ni/Pt(111) > Ni/Pt(111).•NiO1–x/Pt/M/Pt(111) is more reactive than that of Ni/Pt(111).CO oxidation on bimetallic and metal oxide has drawn much attention in the past years due to its importance both technologically and theoretically, but the active phase as well as the detailed reaction mechanism on the bimetallic surface oxide (i.e., a sandwich-like surface structure) are still unclear. In this work, the CO oxidation on the various Pt–Ni model catalysts [including Pt(111), Pt/Ni/Pt(111), Ni/Pt(111), NiO1 − x/Pt(111) and NiO1 − x/Pt/Ni/Pt(111)] was studied by performing the density functional theory calculations. It was found that the CO oxidation reaction would process with a higher reaction barrier on metals at lower oxygen coverage via the Langmuir-Hinshelwood (L-H) mechanism, whereas CO oxidation reaction would take place with a lower barrier at higher oxygen coverage on metals or in the presence of molecular oxygen/CO (on NiO1 − x-like systems) via the Eley-Rideal mechanism. The calculation results show that the activation energy of CO oxidation follows the order: Pt(111) (0.75 eV) > Pt/Ni/Pt(111) (0.69 eV) > Ni/Pt(111) (0.47 eV at 1 ML oxygen), which is in general agreement with the experimental observations. On the surface oxide NiO1 − x/Pt(111) and NiO1 − x/Pt/Ni/Pt(111) systems, it was found that the molecular CO can subtract the surface lattice oxygen to form CO2 spontaneously through the Eley-Rideal mechanism on NiO1 − x/Pt/Ni/Pt(111), whereas such kinetic behavior cannot occur on the NiO1 − x/Pt(111) system, suggesting the high reactivity of CO oxidation on NiO1 − x/Pt/Ni/Pt(111). The possible reason was analyzed by the magnitude of surface oxygen vacancy formation energy, namely NiO1 − x/Pt/M/Pt(111) with relatively low vacancy formation energy as compared to that of NiO1 − x/Pt(111) (3.46 vs 4.51 eV). Moreover, we extend the above study to a more general case in which the subsurface metals in NiO1 − x/Pt/M/Pt(111) system including VIII group metals like Fe/Co/Ni and the IB group metals like Cu, and it was found that the molecular CO can subtract the surface lattice oxygen atom to form CO2 spontaneously via the E-R reaction mechanism for all these NiO1 − x/Pt/M/Pt(111) systems.For the surface oxide system NiO1 − x/Pt/M/Pt(111) (M = Fe, Co, Ni, and Cu), it was found that the molecular CO can subtract the surface lattice oxygen atom to form CO2 spontaneously via the E-R reaction type.

•Initial step of ethanol decomposition on Mo2C is the scission of the OH/CβH bond.•Acetaldehyde formation through the processes of CH3CH2OH → CH3CH2O → CH3CHO.•Ethene formation via the processes of CH3CH2OH → CH2CH2OH → CH2CH2 + OH.•Barrier of CC bond broken decreases as the losing of H atoms in intermediate.The mechanism of ethanol decomposition on α-Mo2C(1 0 0) surface has been systematically studied by using density functional theory (DFT) calculations. The calculation results indicate that ethanol decomposition on Mo2C catalyst starts with the scission of the OH bond and CβH bond scission, and the formation mechanism of the main products like acetaldehyde, hydrogen, and ethylene as well as the by products like methane, ethane and CO was investigated in detail. The acetaldehyde formation through the processes of CH3CH2OH → CH3CH2O → CH3CHO with the highest energy barrier of 0.28 eV, ethene formation via the processes of CH3CH2OH → CH2CH2OH → CH2CH2 + OH with the largest energy barrier of 0.45 eV, and the hydrogen formation through the reaction of 2H → H2 with the energy barrier of 0.76 eV. For the by-products, methane formation through the mechanism of CH3CHO → CH3CO → CH2CO → CHCO → CH → CH2 → CH3 → CH4 with the highest energy barrier of 0.79 eV, ethane formation via the processes of C2H4 → C2H5 → C2H6 with the largest energy barrier of 1.51 eV, and CO formation controlled by its desorption energy of 2.67 eV. The formed O/OH species can act as the oxidative agent to enhance the OH bond scission involved in ethanol, and thus complete the whole reaction processes. Moreover, it was found that the barrier of CC bond broken decreases as the losing of H atoms in intermediate, which indicated that the CC bond broken may become possible at the late dehydrogenation steps in the whole reaction processes.

Three possible pathways for C–N bond breaking in methylamine have been investigated over clean Mo(100) and nitrogen atom-modified Mo(100) surfaces with a nitrogen coverage of 0.25 monolayer (ML) (N–Mo(100)) firstly, and the C–N bond breaking following the intramolecular hydrogen transfer from the CH3 to NH2 is excluded owing to the high barriers. Then methylamine decomposition starting with C–H, N–H, and C–N scission over the nitrogen atom-modified Mo(100) surface with a nitrogen coverage of 0.5 ML (2N–Mo(100)) has been systematically investigated, and the decomposition network has been mapped out. The thermochemistry and energy barriers for all the elementary steps, starting with C–H, N–H, and C–N scission, and sequential reactions from the resulting intermediates, are presented here. The most likely decomposition path is H3CNH2 → H2CNH2 + H → HCNH2 + H + H → CNH2 + H + H + H → C + NH2 + H + H + H → C + NH3 + H2 → C + NH3(g) + H2(g). For the decomposition reactions involved in the likely decomposition path, there is a linear relationship between the energy of transition state and the energy of final state. For the reverse processes of the dehydrogenation of CH, NH, NH2, it is found that there is a linear relationship between the barrier and the valency of A (AC, N, and NH).

Bimetallic alloys such as Au/Pt are known as an efficient catalyst for promoting cyclohexene dehydrogenation to benzene. In this work, we try to understand the unique high reactivity of the Au/Pt surface by the first-principles density functional theory (DFT) calculations. Our DFT results and microkinetic model analysis show that the model modified by carbon and hydrogen was significantly improved in the explanation of the experimental results, and the barriers of rate-determining step (rds) are 1.37, 1.08, and 1.05 eV on Pt(100), 2Pt/Au(100), and Au/Pt (100), respectively. This is in general agreement with the order of the benzene formation rate: Pt(100) < 2Pt/Au(100) < Au/Pt(100). Additionally, the possible reaction mechanism of carbon formation on the Pt surface has been gained in this work for the first time, that is, C6H6 → C6H5 → C6H4 → C6H3 → C + C5H3, and the rate-determining step is the first dehydrogenation step with the energy barrier of ca. 1.80 eV.

The fuzzy symmetries of two kinds of linear polyacene molecules are probed into in the paper. In these molecules, any one of the benzene rings abreast connects at most other two rings in two ways: either its two opposite C–C bonds combine with two other rings, respectively, or its two meta-position C–C bonds connect two rings in cis- and trans-form, respectively. The former is called p-polyacenes (or straight polyacenes), and the latter is m-polyacenes (or kinked ones). It can be thought as the planar molecule with approximate one-dimensional space periodic transformation (parallel translation) symmetry, namely, group \({{\rm G}_{1}^{2}}\) symmetry, when the number of its benzene ring is very large; on the other hand, it can be considered as the fuzzy group \({{\rm G}_{1}^{2}}\) symmetry, if the benzene ring number is not large enough. The p-polyacene and m-polyacene with 20 benzene rings are analyzed as typical examples, and the energies of the π-molecular orbital (MO) and the fuzzy symmetry characters related to the space symmetry transformations are carefully examined. Moreover, the π-MOs of the p-polyacenes and m-polyacenes with different numbers of benzene ring are investigated to obtain the related rules.

The adsorption and decomposition of methylamine on Ni(1 1 1), Ni(1 0 0), stepped Ni(1 1 1), and nitrogen atom modified Ni(1 0 0) (denoted N–Ni(1 0 0)) have been studied with the DFT–GGA method using the periodic slab models. The initial scissions of C–H, N–H and C–N bond are considered. The adsorption energies under the most stable configurations for the possible species and the activation energies for the possible initial elementary reactions involved are obtained in the present work. Through systematic exploring of the kinetics mechanism of methylamine decomposition on these four surfaces, it is found that the reactivity of these surfaces decreased with the order of stepped Ni(1 1 1) > Ni(1 0 0) > Ni(1 1 1) > N–Ni(1 0 0). This indicates that the reactivity is related to the openness of the surface, and the presence of nitrogen atom reduces the reactivity of the Ni(1 0 0). For the three reactions, the barriers decreased with the order of C–N > N–H > C–H on Ni(1 1 1) and Ni(1 0 0), whereas they decreased with the order of C–N > C–H > N–H on stepped Ni(1 1 1) and N–Ni(1 0 0).

The DFT-GGA calculations have clearly reproduced the experimentally observed structure-sensitivity of forward and reverse water-gas shift reactions on Cu(111), Cu(100), and Cu(110) assuming the “redox mechanism”. The reason for the structure-sensitivity has also been explored by the transition-state structure analysis and the metal d-band center analysis. It is concluded that the difference in virtual adsorption energy of atomic oxygen or other strongly adsorbed species at the transition state is essential to account for the structure-sensitive reactions.Keywords (keywords): copper; density functional theory calculation; structure sensitivity; water−gas shift reaction;

The chemisorption of radical species (CH3, CH3O, and HCOO) on Ni(1 1 1), Ni(1 0 0), and Ni(1 1 0) surfaces has been systematically studied by means of self-consistent, periodic, density functional theory (DFT–GGA) calculations. The calculated results showed that the adsorption energies are structure sensitive to the surface structure, that is, Ni(1 1 1) < Ni(1 0 0) < Ni(1 1 0) for CH3O and HCOO species, and Ni(1 0 0) < N(1 1 1) < Ni(1 1 0) for CH3 species. In addition, it is found that the adsorption energy of CH3O is larger than that of CH3 on a given metal surface.

First principles density functional theory calculations have been performed for the chemisorption of formate adsorption on some metal surfaces. For the most stable adsorption site of short- bridge, the calculated formate adsorption energy follows the order of Au(110) < Ag(110) < Cu(110) < Pd(110) < Pt(110) < Ni(110) < Rh(110) < Fe(100) < Mo(100), and a clear linear correlation exists between the adsorption energy and the corresponding heat of formation of metal oxides. Moreover, it has been found that the formate adsorption energy for the transition metals can be correlated well with its d-band center (ɛd), and the IB Group metals can be described by the coupling matrix element square (Vad2).

A systematic theoretical study of CH3S adsorbed on the (1 1 1) surface of some transition metal surfaces (Pd, Pt, Rh, Ni) and on the Mo(1 0 0), Ru(0 0 0 1) surfaces is presented, and a consistent picture for some key physical properties determining the reactivity of metals appears. The calculated adsorption energies are quite in agreement with the experimental data as well as the previous theoretical calculation results. Importantly, our results showed that the CH3S adsorption energy on transition metal surfaces can be linearly correlated with the metal electronic properties such as d-band center, and the possible reason of difference in the adsorption bonding is suggested by analyzing the nature of chemisorption. Additionally, we have compared the adsorption energy difference between CH3O and CH3S.

The surface-structural sensitivity of the reverse water-gas shift (RWGS) reaction (CO2 + H2 → CO + H2O) over the Cu(1 1 1), Cu(1 0 0), and Cu(1 1 0) surfaces has been studied by first-principle density functional calculations together with the UBI-QEP approach. Cluster models of the surface have been employed to simulate the adsorption of CO2, H2, H, O, OH, CO, and H2O on the Cu(hkl) surfaces at low coverage. This sensitivity is determined by the difference in the activation barriers. It can be noticed that the most likely rate-determining step in RWGS reaction is the CO2 dissociative adsorption, namely CO2,g → COs + Os. The trend in the calculated activation barriers for the reaction of CO2 dissociative adsorption follows the order of Cu(1 1 0) < Cu(1 0 0) < Cu(1 1 1), suggesting that the most efficient crystal surface for catalyzing RWGS reaction by copper is Cu(1 1 0), and the more densely packed Cu(1 1 1) surface is the least active among the Cu(hkl) surfaces studied here. As expected, the activation barriers for the recombinative reactions over Cu(hkl) are in the order of Cu(1 1 0) > Cu(1 0 0) > Cu(1 1 1), just opposite to the dissociative reactions. The interesting thing is that there is a good correlation between the adsorption bond length and the adsorption energy: The preferred adsorption site is the one with the shortest adsorption bond length. The present calculations are in good agreement with experimental observations.

The adsorption properties of atomic and molecular species on Ir4/MgO and Ir4/γ-Al2O3 have been systematically studied by means of planewave density functional theory (DFT) calculations using the periodic boundary conditions. The binding energies of these species were ordered as follows: H2O