DFT Simulations of Water Adsorption and Activation on Low‐Index α‐Ga2O3 Surfaces

Density functional theory (DFT) calculations are used to explore water adsorption and activation on different α‐Ga₂O₃ surfaces, namely (001), (100), (110), and (012). The geometries and binding energies of molecular and dissociative adsorption are studied as a function of coverage. The simulations reveal that dissociative water adsorption on all the studied low‐index surfaces are thermodynamically favorable. Analysis of surface energies suggests that the most preferentially exposed surface is (012). The contribution of surface relaxation to the respective surface energies is significant. Calculations of electron local density of states indicate that the electron‐energy band gaps for the four investigated surfaces appears to be less related to the difference in coordinative unsaturation of the surface atoms, but rather to changes in the ionicity of the surface chemical bonds. The electrochemical computation is used to investigate the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) on α‐Ga₂O₃ surfaces. Our results indicate that the (100) and (110) surfaces, which have low stability, are the most favorable ones for HER and OER, respectively.     

Density Functional Investigations into the Adsorption of Methanol on Isomorphously Substituted ZSM—5

The adsorption of methanol in the acid sites of zeolites has attracted a great deal of attention because of its relevance to the industrial methanol to gasoline conversion process. In this work, the B3LYP hybrid density functional method was used to investigate the adsorption behavior of methanol on Bronsted acid sites in B, Al, Ga and Fe isomorphously substituted ZSM-5 zeolites. The optimized structures reveal a physisorbed methanol interacting with the zeolite framework through two hydrogen bonds. The order of the computed adsorption energy correlates with the acid strength of the isomorphously substituted ZSM-5: B-ZSM-5《Fe-ZSM-5相似文献   

A DFT Investigation on Hydrogen Adsorption Based on Alkali-metal Organic Complexes

Using density functional theory calculation based on the B3LYP method,we have studied the interactions of H2 molecules with alkali-metal organic complexes C6H6-nLin(n = 1～3),C6H5Na and C6H5K.A significant part of the electronic charge of M s orbital(Li 2s,Na 3s,K 4s) is donated to phenyl and is accommodated by H2 bonding orbital.For all the complexes considered,each bonded alkali-metal atom can adsorb up to five H2 in molecular form with the mean binding energy of 0.59,0.55 and 0.56 eV/H2 molecule for C6H6-nLin(n = 1～3),C6H5Na and C6H5K,respectively.The kinetic stability of these hydrogen-covered organometallic complexes is discussed in terms of energy gap between HOMO and LUMO.It is remarkable that these alkali-metal organic complexes can store up to 23.80 wt% hydrogen.Therefore,the complexes studied may be used as hydrogen storage materials.     

CO2在Cu表面还原成碳氢化合物的DFT计算研究

应用密度泛函理论（DFT）反应能计算及最小能量路径分析研究了CO2在气相和电化学环境中于Cu(111)单晶表面的还原过程。气相中,CO2还原为碳氢化合物的反应路径可能为：CO2(g) + H* → COOH* → (CO +OH)* → CHO*;CHO + H* → CH2O* → (CH2 + O)*;CH2* + 2H* → CH4或2CH2* → C2H4。整个反应由CO2(g) + H* → COOH* → (CO +OH)*,(CO + H)* → CHO*和CH2O* → (CH2 + O)*等几个步骤联合控制。在-0.50V (vs RHE) 以正的电势下,CO2在Cu(111)表面电化学还原主要形成HCOO-和CO吸附物;随着电势逐渐负移,CO2加氢解离形成CO的反应越来越容易,CO成为主要产物;随电势进一步变负,形成碳氢化合物的趋势逐渐变强。与CO2的气相化学还原不同的是,电化学环境下CO质子化形成的CHO中间体倾向于解离形成CH,而在气相中CHO中间体则倾向于进一步质子化形成CH2O中间体。     

Comparative Study of Hypophosphite H2PO2^- Adsorption on Ni（111） and Ag（111） Surfaces by DFT

Surface structures and electronic properties of hypophosphite H2PO2^- on Ni（111） and Ag（111） surfaces were investigated by means of density functional theory at B3LYP/6-31 ＋ ＋G（d,p） level. The most stable structure was that in which the H2PO2^- adsorbs with its two P--O bonds faced to the substrate surface. The results of the Mulliken population analysis showed that because of the subtle difference of electron configuration, the adsorption energy was larger on the Ni surface than on the Ag surface, and the amounts of both donation and back donation were larger on the Ni（111） surface than on the Ag（111） surface. There were more negative Mulliken charge transfer from H2PO2^- to substrate clusters on Ni surface than on Ag surface and more positive Mulliken charges on P atom in Ni4H2PO2^- than in Ag4H2PO2^-, which means that P atom in Ni4H2PO2^- is easily attacked by a nucleophile such as OH . Thus, H2PO2^- is more easily oxidated on Ni（111） surface than on Ag（111） suface. These results indicated that the silver surface is inactive for the oxidation reaction of the hypophosphite anion.     

甲醇在Au(111)表面吸附的密度泛函研究

 采用基于第一性原理的密度泛函理论和周期平板模型相结合的方法,对CH3OH分子在Au(111)表面top, fcc, hcp和bridge位的吸附模型进行了构型优化、能量计算以及Mulliken布居分析,结果表明top位是较有利的吸附位. 吸附的CH3OH解离产生甲氧基CH3O和H, 对它们在Au(111)面的吸附进行的计算表明, bridge和fcc位分别是二者的最佳吸附位. 对过渡态的计算给出了CH3OH在Au表面解离吸附的可能机理: 首先发生 O-H 键的断裂,继而生成甲氧基中间体.     

Quantum Chemical Study of Water Adsorption on the Surfaces of SrTiO3 Nanotubes

We have studied the adsorption of water molecules on the inner and outer surfaces of nanotubes generated by rolling (001) layers of SrTiO₃ cubic crystals. The stability and the atomic and electronic structures of the adsorbed layers are determined by using hybrid density functional theory. The absorption energy and the preferred adsorbate structure are essentially governed by the nature of the surface of the nanotube. Dissociative adsorption prevails on the outer nanotube surfaces. The stability of the adsorbed layers on the inner surfaces is related to the possibility of the formation of hydrogen bonds between water molecules and surface oxygen atoms, and depends on the surface curvature. The presence of water molecules on the inner surface of the nanotubes leads to an increase of the electronic band gap. Externally TiO₂‐terminated nanotubes could be used for the photocatalytic decomposition of water by ultraviolet radiation.     

DFT Study of Alkali Metal Atom Adsorption on Defect-Free MgO(001) Surface

The adsorption of isolated alkali metal atoms (Li, Na, K, Rb, and Cs) on defect-free sur-face of MgO(001) has been systemically investigated with density functional theory using a pseudopotential plane-wave approach. The adsorption energy calculated is about -0.72 eV for the lithium on top of the surface O site and about one third of this value for the other alkali metals. The relatively strong interaction of Li with the surface O can be explained by a more covalent bonding involved, evidenced by results of both the projected density of states and the charge density difference. The bonding mechanism is discussed in detail for all alkali metals.     

The Effect of Pristine and Hydroxylated Oxide Surfaces on the Guaiacol HDO Process: A DFT Study

The acid-base character of oxide supports is crucial for catalytic reactions. In this work, the acid-base properties of five oxide surfaces common in heterogeneous catalysis were investigated and related to their interaction with monolignol compounds derived from lignin. We have used density functional theory simulations also to understand the role of the surfaces’ hydroxylation state. The results show that moderate hydroxyl coverage on the amphoteric γ-Al₂O₃ (110) slightly strengthens the oxy-compounds’ adsorption due to an increase in Lewis acidity. Similarly, low hydroxyl coverage on the reducible TiO₂ (101) enlarges its adsorption capacity by up to 42 % compared with its clean surface. The higher affinity is attributed to the more favourable interaction between the surface-OH groups and the aromatic rings. Overall, the results indicate that hydroxyl coverage enhances the amphoteric and reducible adsorption capacity towards aromatic species.     

Density functional theory (DFT) investigation of the adsorption of the CH3OH/Au(100) system

The adsorption of methanol on flat Au (100) surface with different coverages (θ = 1.0, 0.5 and 0.25 monolayer (ML)) is studied using density functional theory. Among the three sites (top, bridge and hollow) and coverages investigated in the present work, no adsorption is stable for θ = 1.0 ML. The most energetically preferred site of adsorption for CH₃OH is found to be the hollow site for coverages of 0.25 ML and 0.50 ML. We also find that for all adsorption sites, an increase in CH₃OH coverage triggers a decrease in the adsorption energy. The geometric parameters, local density of states and work function changes are analysed in detail. The coadsorption of methoxy and hydrogen has also investigated. In addition, the dissociation of methanol on Au(100) has been studied, and an activation energy was found to be 1.72 eV. This result compare with existing data in the literature for Au(111) surface. Copyright © 2013 John Wiley & Sons, Ltd.     

Effect of Hydrogen on O2 Adsorption and Dissociation on a TiO2 Anatase (001) Surface

The effect of hydrogen on the adsorption and dissociation of the oxygen molecule on a TiO₂ anatase (001) surface is studied by first‐principles calculations coupled with the nudged elastic band (NEB) method. Hydrogen adatoms on the surface can increase the absolute value of the adsorption energy of the oxygen molecule. A single H adatom on an anatase (001) surface can lower dramatically the dissociation barrier of the oxygen molecule. The adsorption energy of an O₂ molecule is high enough to break the O?O bond. The system energy is lowered after dissociation. If two H adatoms are together on the surface, an oxygen molecule can be also strongly adsorbed, and the adsorption energy is high enough to break the O?O bond. However, the system energy increases after dissociation. Because dissociation of the oxygen molecule on a hydrogenated anatase (001) surface is more efficient, and the oxygen adatoms on the anatase surface can be used to oxidize other adsorbed toxic small gas molecules, hydrogenated anatase is a promising catalyst candidate.     

Density Functional Theory Study of the Adsorption of C2H2 on the Cu/Pt(111) Bimetallic Surfaces

We applied periodic density-functional theory to investigate the adsorption of C2H2 on the Cu/Pt bimetallic and monometallic surfaces, including Cu-Pt-Pt and Pt-Cu-Pt representing the monolayer Cu on the Pt surface and subsurface Cu in the Pt surface, respectively. For the Pt(111) and Pt-Cu-Pt surfaces, C2H2 is preferentially a 3-fold "parallel-bridge" configuration, and a "μ-bridge" structure exists above the Cu(111) and Cu-Pt-Pt surfaces. The adsorption energy of C2H2 on these surfaces decreases in the order Pt(111) > Cu-Pt-Pt > Pt-Cu-Pt > Cu(111). The analysis of density of states, charge, and vibrational frequencies showed obviously weakening of the adsorbed C-C bond and high sp2 character on the carbon atom. Furthermore, when the top-layer compositions are equal, the nearer the EF d-band center is, the larger the C2H2 adsorption energy will be.     

Density Functional Theory Study on the Adsorption of CN on Transition Metal M（100） （M = Ni,Pd, Pt,Cu, Ag and Au） Surfaces

The adsorption of cyanide on the top site of a series of transition metal M（100） （M = Cu, Ag, Au, Ni, Pd, Pt） surfaces via carbon and nitrogen atoms respectively, with the CN axis perpendicular to the surface, has been studied by means of density functional theory and cluster model. Geometry, adsorption energy and vibrational frequencies have been determined, and the present calculations show that the adsorption of CN through C-end on metal surface is more favorable than that via N-end for the same surface. The vibrational frequencies of CN for C-down configuration on surface are blue-shifted with respect to the free CN, which is contrary to the change of vibrational frequencies when CN is adsorbed by N-down structure. Furthermore, the charge transfer from surface to CN causes the increase of surface work function.     

A DFT Study of Thiophene Adsorption on the Rh（111） Surfaces

Thiophene adsorption on the Rh(111) surfaces has been investigated by density functional theory.The results show that the adsorption at the hollow and bridge sites is the most stable.The molecular plane of the thiophene ring is distorted,the C=C bond is stretched to 1.448  and the C-C bond is shortened to 1.390.The C-H bonds tilt 22～42oaway from the surface.The calculated adsorption geometries are in reasonable agreement with population analysis and density of states.The thiophene molecule obtains 0.74 electrons,reflecting the interaction between the lone pair of sulfur and the d-orbitals of metal.The reaction paths and transition states for desulfurization of the molecule have been investigated.The bridge adsorption structure of thiophene leads to a thiol via an activated reaction with an energetic barrier of 0.30 eV.This second step is slightly difficult,and dissociation into a C4H4 fragment and a sulfur atom is possible,with an energetic barrier of 0.40 eV.     

Efficient Disproportionation of Formic Acid to Methanol Using Molecular Ruthenium Catalysts

The disproportionation of formic acid to methanol was unveiled in 2013 using iridium catalysts. Although attractive, this transformation suffers from very low yields; methanol was produced in less than 2 % yield, because the competitive dehydrogenation of formic acid (to CO₂ and H₂) is favored. We report herein the efficient and selective conversion of HCOOH to methanol in 50 % yield, utilizing ruthenium(II) phosphine complexes under mild conditions. Experimental and theoretical (DFT) results show that different convergent pathways are involved in the production of methanol, depending on the nature of the catalyst. Reaction intermediates have been isolated and fully characterized and the reaction chemistry of the resulting ruthenium complexes has been studied.     

Adsorption of 1,3‐Benzenedithiol and 1,3‐Benzenedimethanethiol on Gold Surfaces

The adsorption characteristics of 1,3‐benzenedithiol (1,3‐BDT) and 1,3‐benzenedimethanethiol (1,3‐BDMT) on Au surfaces are investigated by means of surface‐enhanced Raman scattering, UV/Vis absorption spectroscopy, and cyclic voltammetry (CV). 1,3‐BDMT is found to adsorb via two S–Au linkages at concentrations below monolayer coverage, but to have an upright geometry as the concentration increases on Au nanoparticles. On the other hand, 1,3‐BDT is found to adsorb by forming two S–Au linkages, regardless of concentration, based on the disappearance of the ν(SH)_free stretching band. Because of the absence of the methylene unit, 1,3‐BDT appeares not to self‐assemble efficiently on Au surfaces. The UV/Vis absorption spectroscopy and CV techniques are also applied to check the formation of self‐assembled monolayers of 1,3‐BDT and 1,3‐BDMT on Au. Density functional theory calculations based on a simple adsorption model using an Au₈ cluster are performed to better understand the nature of the adsorption characteristics of 1,3‐BDT and 1,3‐BDMT on Au surfaces.     

甲醇在Pt-Fe(111)/C表面吸附的理论研究

采用密度泛函理论和周期平板模型相结合的方法, 对CH3OH分子在Pt-Fe(111)/C表面top, fcc, hcp和bridge位的吸附模型进行了构型优化、能量计算, 结果表明bridge位是较有利的吸附位. 掺杂后费米能级的位置发生了右移, 价带和导带均增宽, 极利于电子-空穴的迁移, 这对提高催化活性是非常有利的. 考察抗中毒性发现: CO在Pt(111)/C面上的吸附能比甲醇吸附能要高, CO在Pt-Fe(111)/C的吸附能比甲醇吸附能要低, 可说明CO在Pt(111)/C面上有中毒效应, 而Pt-Fe(111)/C的抗CO中毒能力增强, 是催化氧化甲醇良好的催化剂.     

Adsorption Sequence of Multifunctional Groups: A Study on the Reaction Pathway and the Adsorption Structure of Homocysteine on the Ge(100) Surface

We investigated the adsorption mechanism of homocysteine (HS? CH₂? CH₂? CH(NH₂)? COOH) on the Ge(100) surface along with its electronic structures and adsorption geometries to determine the sequence of adsorption of this amino acid′s functional groups using core‐level photoemission spectroscopy (CLPES) in conjunction with density functional theory (DFT) calculations. We found that the “SH‐dissociated OH‐dissociated N‐dative‐bonded structure” and the “SH‐dissociated OH‐dissociation‐bonded structure” were preferred at a monolayer (ML) coverage of 0.30 (lower coverage) and 0.60 (higher coverage), respectively. The “SH‐dissociated OH‐dissociated N‐dative‐bonded structure” was the most stable structure. Moreover, we systematically confirmed the sequence of adsorption of the functional groups of the homocysteine molecule on the Ge(100) surface, which is thiol group (? SH), carboxyl group (? COOH), and amine group (? NH₂).     

V_2O_5/CeO_2催化剂上甲醇氧化一步法合成二甲氧基甲烷

采用溶胶-凝胶法制备了V2O5/CeO2催化剂,并用于甲醇氧化一步法合成二甲氧基甲烷(DMM)反应中.考察了V2O5含量对钒氧化物的存在状态、催化剂表面酸性、氧化-还原性及其催化甲醇氧化反应性能的影响.结果表明,V2O5含量为15%时钒氧化物呈单层分散,小于15%时以孤立或聚合态存在,大于20%时出现V2O5晶体,达到30%时出现CeVO4.当V2O5含量为15%时,较高的钒氧化物分散度使催化剂具有较强的氧化还原能力和较多的酸性中心,从而使催化剂具有较高的活性和DMM选择性.     

Hydrogen Adsorption on Ti Decorating Benzene Grafted Tetrahydrido-silsequioxanes

A novel type of Ti decorating benzene grafted tetrahydrido-silsequioxane struc-tures was designed and investigated using density functional theory(DFT).The hydrogen adsorption properties of this new material were investigated at the same level of theory.The results reveal that up to four hydrogen molecules(with the restrict of 18 electrons rule) can be adsorbed on each Ti atom of(TiC6H5)m-H4-mSi4O6(m = 1-4) molecular systems with the average binding energies of 0.691,0.692,0.693 and 0.695 eV for m = 1-4,respectively.The variations of HOMO- LUMO energy gaps verify that the host structures with four H2 molecules adsorbed own the best kinetics stability.The interaction mechanism of H2 molecules with the host materials mainly attributes to the well-known "kubas interactions".All the results indicate that the complex structures designed here may be used as hydrogen storage materials at ambient conditions.