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A new thermodynamics-kinetics relation called adsorbate-dependent barrier scaling (ADBS) relation is discovered and used to predict the catalytic activity of a series of In2O3-supported metal and alloy catalysts for CO2 hydrogenation to methanol.

Organophotoredox catalytic four-component radical-polar crossover cascade reactions for the stereoselective synthesis of β-amido sulfones with high atom-, step-, and redox economy and excellent diastereoselectivity.

Scaling relations play a vital role in high-throughput screening of catalytic materials, and more and more attention is being paid to strain-based regulation of catalytic performance. Here we investigated the variation of several energetics, including adsorption energies in the initial state, transition state, and final state, reaction energies, and energy barriers with strain, by studying CO, BH, NH, CH, and NO adsorption and dissociation on M(111) (M = Cu, Ag, Ni, Pd, or Pt) surfaces. We show that energy barriers, reaction energies, and adsorption energies can vary either linearly or nonlinearly (quadratically) with strain. Systems with stronger adsorbate-substrate interaction and weaker atom-atom interaction in substrates are more likely to exhibit nonlinear relations. The well-known Brønsted-Evans-Polanyi relationships and transition state scaling relationships under strain were also examined, and both of them can be nonlinear under strain, in principle. The observed nonlinear relationships were satisfactorily rationalized with the equations derived from Mechanics of Solids.

Mechanistic study on the catalytic hydroboration of imine by a pincer-type phosphorus compound 1NP was performed through the combination of DFT and DLPNO-CCSD(T) calculations. The reaction proceeds through a phosphorus-ligand...

Metal-free catalysts composed of heavy main group element(s) have been limited. Herein, a theoretical study unveils that pincer-type phosphorus compound bearing a boryl-pendant is good catalyst for H-2 generation from ammonia borane through phosphorus-boryl (P-B) cooperation function. Pincer-type phosphorus compound without boryl-pendant is not active for this reaction, indicating the important role of the P-B cooperation function.

More and more attention has been paid to strain-based regulation of catalytic activity. To guide regulation of catalytic performance via strain engineering, adsorption and reactions of AHx (A = C, N, O, x ≤ 3) were investigated on uniformly strained In

A green and practical divergent Ritter-type amination via a photoredox catalytic four-component radical-polar crossover process was developed. This versatile protocol presents a modular and powerful strategy to access functionalized β-sulfonyl imides and imines under mild conditions from readily available and stable substrates with high atom-, step- and redox economy. We manipulated carboxylic acids and benzotriazoles to precisely attack the nitrilium ion instead of the carbocation, thus preventing many complicated side reactions of the photocatalytic reactions. Furthermore, the synthetic utility of this divergent Ritter reaction is further demonstrated by the late-stage modification of pharmaceutical and natural product derivatives.

Density functional calculations and microkinetic simulations were performed on the transformation network of acetylene on Pd(111), M(111) and PdM(111) (M = Cu, Ag, Au) surfaces. It is demonstrated that the adsorption energies on alloy surfaces linearly correlate with the values on the pure metal surfaces. A good linear relationship between the co-adsorption energies of initial states and transition states is revealed with which the barriers of most elementary steps in the reaction network were estimated. To shed light on the transformation of acetylene, microkinetic simulations were conducted on the network. The results show that CHCH and H are dominant species on the surfaces and CCH, CCH

Molecular geometries and electronic structure calculations and spectroscopic assignments for metallonaphthalocyanines NiNc, CuNc and ZnNc are performed on the optimized geometries at B3LYP/6–31G* level. The order of the bond lengths of the N M bonds is computed to be NiNc CuNc > ZnNc, which is in reverse sequence of the N–M bond length. The strongest Raman lines predicted at 1570 (NiNc), 1546 (CuNc) and 1525 (ZnNc) cm−1 are highly sensitive to the metal ion. Comparison of the calculated properties of MNcs and MPcs (metallphthalocyanines) compounds reveals some interesting and meaningful results due to extension of the conjugated systems.

Three red iridium(iii) complexes with dithiocarbamate ligands were rapidly synthesized at room temperature with good yields, and their OLEDs exhibit an EQEmax of 30.54% with mild efficiency roll-off., Three red cyclometalated iridium(iii) complexes (4tfmpq)2Ir(dipdtc), (4tfmpq)2Ir(dpdtc) and (4tfmpq)2Ir(Czdtc) (4tfmpq = 4-(4-(trifluoromethyl)phenyl)quinazoline, dipdtc = N,N-diisopropyl dithiocarbamate, dpdtc = N,N-diphenyl dithiocarbamate, and Czdtc = N-carbazolyl dithiocarbamate) containing the unique four-membered Ir–S–C–S backbone ring were synthesized in five minutes at room temperature with good yields, and the Gibbs free energy calculation results indicate that all reactions are exothermic and thermodynamically favorable processes. The emission colors (λpeak = 641–611 nm), photoluminescence quantum efficiencies (ΦP = 58.3–93.0%) and bipolar properties can be effectively regulated by introducing different electron-donating substituents into the dithiocarbamate ancillary ligands. Employing these emitters, organic light emitting diodes (OLEDs) with double emissive layers exhibit excellent performances with a maximum brightness over 60 000 cd m–2, a maximum current efficiency of 40.68 cd A–1, a maximum external quantum efficiency (EQEmax) of 30.54%, and an EQE of 26.79% at the practical luminance of 1000 cd m–2. These results demonstrate that Ir(iii) complexes with sulfur-containing ligands can be rapidly synthesized at room temperature, which is key to the production of metal luminescent materials for large-scale application in highly efficient OLEDs.

CoIII(salen)-X (X = Cl-, OAc-, and OTs-) mediated hydration of propylene oxide (PO) to propylene glycol has been investigated in detail using density functional theory (DFT) calculations. Two kinds of reaction mechanisms, the concerted and stepwise pathways, were scrutinized. For the eight concerted routes, the cooperative bimetallic route in which the middle carbon atom is attacked by the nucleophilic oxygen atom (route VI-m) was calculated to be the most favorable, and among the three catalysts examined H2O-CoIII-OTs was found to be the most active, due to the strong hydrogen bonding between the nucleophilic H2O and the ring oxygen atom in the epoxides as well as the extra π-π stacking interaction. For the stepwise mechanism which consists of the formation of H2O-CoIII-OH, the ring-opening of PO and propylene glycol formation, our studies reveal that different H2O-CoIII-Xs behave kinetically very similarly in the course of propylene glycol formation, but show a notable difference in the rate of H2O-CoIII-OH formation with Cl-OAc-OTs-. The rate ordering with which we rationalize the experimental phenomena well is disclosed to be consistent with the nucleophilicity of the counterions by molecular electrostatic potential, condensed Fukui function and condensed local softness. We show that the nucleophilicity of the counterion determines the favorable mechanism that PO hydration follows.

We studied the ring opening of propylene oxide (PO) by salen-M coordinated OH- group [M = Al(Ⅲ), Sc(Ⅲ), Cr(Ⅲ), Mn(Ⅲ), Fe(Ⅲ), Co(Ⅱ), Co(Ⅲ), Ni(Ⅱ), Cu(Ⅱ), Zn(Ⅱ), Ru(Ⅲ) and Rh(Ⅲ)]. The results show that the ring opening energy barriers for M(II) complexes are much lower than those with M(III) complexes in the gas phase, and the barriers correlate linearly with the negative charges on the OH- group, the Fukui function condensed on the OH- group. The nucleophilicity ordering in gas phase can be rationalized by the ratio of formal positive charges/radius of M cations. Solvent effect greatly increases the barriers of M(II) complexes, but slightly changes the results of M(III) ones, making the barriers similar. Analysis indicates that the reaction heats are linearly proportional to the reverse reaction barriers. The relationships established here can be used to estimate the ring opening barriers and to screen epoxide ring opening catalysts.

Summary We report here a supercatalyst for oxygen reduction of Pt/CNx/Ni in a unique ternary heterostructure, in which the Pt and the underlying Ni nanoparticles are separated by two to three layers of nitrogen-doped carbon (CNx), which mediates the transfer of electrons from the inner Ni to the outer Pt and protects the Ni against corrosion at the same time. The well-engineered low-Pt catalyst shows ∼780% enhanced specific mass activity or 490% enhanced specific surface activity compared with a commercial Pt/C catalyst toward oxygen reduction. More importantly, the exceptionally strong tune on the Pt by the unique structure makes the catalyst superbly stable, and its mass activity of 0.72 A/mgPt at 0.90 V (well above the US Department of Energy's 2020 target of 0.44 A/mgPt at 0.90 V) after 50,000 cyclic voltammetry cycles under acidic conditions is still better than that of the fresh commercial catalyst., Graphical Abstract, Highlights • Matched band structures among Pt/CNx/Ni enable electron transfer from Ni to Pt • Enhanced Pt-CNx interaction by underlying Ni prevents Pt from coalescence and oxidation • Encapsulated Ni is protected from corrosion and maintains the structure stability of THS, Catalysis; Electrochemical Energy Conversion; Energy Materials

1,3-butadiene produced during acetylene hydrogenation is detrimental for catalysts. Combining density functional calculations and microkinetic modeling, we examined the formation of 1,3-butadiene from the coupling of various of C2 species on Pd(111) and PdM(111)(M=Cu, Ag, Au). It is demonstrated that the adsorption energies on PdM(111) linearly correlate with the ones on Pd(111). Transition state scaling (TSS) relations (linear relationships between the adsorption energies in the initial/final states and in the transition states) exist for both hydrogenation and coupling reactions. Microkinetic modeling reveals that introducing coinage metals into Pd promotes the selectivity of CH2CH2 and significantly hinders the formation 1,3-butadiene. PdAu shows the best ability to suppress the green oil formation and the catalyst deactivation. CHCH and CHCH2 are the main fragments for the C-C coupling on PdM(111), and CHCH+CHCH2 to CHCHCHCH2 and 2CHCH2 to CH2CHCHCH2 are the main coupling reactions leading to 1,3-butadiene on PdM(111). High temperature and high H2 to CHCH ratio are favorable for inhibition of the green oil formation.

A coordination-dependent interatomic interaction is developed for Ag atoms and applied to simulate Au-Ag alloy nanoparticles ranging from 2.6 nm to 4.5 nm with different composition ratios at different temperatures. Using the lattice Monte Carlo method, we found that Ag segregates preferentially on the edges of nanoparticles. The region-specific segregation is revealed by our study and it indicates that depending on the size and temperature, Ag may segregate on the edges only, whereas its segregation on flat surfaces is negligible. Assuming that equimolar Au-Ag edges maximize the catalytic synergistic effect, we predicted the size and composition dependent optimal reaction temperatures for the Au-Ag catalyzed CO oxidation, which agree with the available experimental temperatures very well. Our study demonstrates that the region-specific segregation not only complements the details of surface segregation but is also very important for the utilization and tuning of faceted bimetallic nanoparticles.

The surface composition and atomic arrangement of heterogeneous catalysts determine the surface chemistry and are necessary information for understanding surface catalytic reactions. Compared with monometallic catalysts, alloy catalysts are more complicated because of possible surface segregation or adsorption-induced segregation which may change under different reaction atmosphere. Construction of reasonable slab models to study reactions on alloy surfaces is of importance. Here we proposed a density functional theory based Monte Carlo method (DFT-MC) and used it to investigate the surface composition and atomic arrangement of the (111) surfaces of 1:1 PdAg, PdAu and PdCu alloys in vacuum and under the acetylene partial hydrogenation conditions modeled by co-adsorption of H and acetylene and of H and ethylene. Our DFT-MC simulations indicate that Au and Ag segregate on the PdAu(111) and PdAg(111) surfaces while Pd is enriched on the PdCu(111) surface under vacuum conditions. The surface Pd contents of PdAg and PdAu tend to increase under partial hydrogenation conditions. Analyses reveal that the co-adsorption energies on the ideal (bulk-cut) surfaces correlate linearly with the values on the segregated surfaces and there is also a linear relationship for the d-band centers between the ideal and segregated surfaces. The present study provides a way to construct more realistic models for studying reactions on alloy surfaces.

The interface interaction between the dimethyl sulfide (DMS) molecule and the gold substrate under external electric fields is investigated by density functional theory method. The polarized DMS adsorbate reduces the work function of the gold substrate while the induced substrate dipole upon the adsorption slightly increases the work function. The DMS layer partially shields the Au(111) substrate from the electric fields and the vacuum level of DMS/Au(111) shifts less than of Au(111) in consequence. Under electric fields pointing outward from the Au(111) surface, both the reduction of work function and the adsorption of DMS molecule are enhanced on the surface. We also suggest the possible application of the field-effect transistor (FET) sensor with gold gate for detecting DMS molecule by utilizing the reduction of substrate work function upon adsorption. The effects of coverage and electric field on the theoretical sensitivity of the sensor are also discussed.

The development of low-cost non-precious-metal electrocatalysts with high activity and stability in the oxygen reduction reaction (ORR) remains a great challenge. Heteroatom-doped carbon materials are receiving increased attention in research as effective catalysts. However, the uncontrolled doping of heteroatoms into a carbon matrix tends to inhibit the activity of a catalyst. Here, the in situ activation of a uniquely structured nitrogen-doped carbon/Ni composite catalyst for the ORR is demonstrated. This well-designed catalyst is composed of a nitrogen-doped carbon shell and embedded metallic nickel. The embedded Ni nanoparticles, dispersed on stable alumina with a high specific surface area for protecting them from agglomeration and in an unambiguous composite structure, are electron-donating and are shielded by the nitrogen-doped carbon from oxidation/dissolution in harsh environments. The electronic structure of the nitrogen-doped carbon shell is modulated by the transfer of electrons at the interface of nitrogen-doped carbon-Ni heterojunctions owing to the Mott-Schottky effect. The electrochemically active surface area result implies that the active sites do not relate to Ni directly and the enhanced catalytic activity mainly arises from the modulation of nitrogen-doped carbon by nickel. XPS and theoretical calculations suggest that the donated electrons are transferred to pyridinic N primarily, which ought to enhance the catalytic activity intrinsically. Benefiting from these transferred electrons, the half-wave potential of the nitrogen-doped carbon/Ni composite catalyst is 94 mV positively shifted compared to the Ni-free sample.

Reactive molecular dynamics simulations were performed to explore the structural evolution of a ZnO nanocluster and (0001) and (1010) surfaces under a H2 atmosphere at different temperatures. The mechanisms of H2 dissociation and water formation were analyzed. Our simulations reveal that there are two pathways for H2 dissociation and three routes for water formation on the surfaces. The nanocluster is more active for H2 dissociation and water formation than the two surfaces. The gas–solid interactions lead to outward displacement of the substrate O atoms. While the O-terminated surface of the (0001) facet is active for H2 dissociation and water formation, the Zn-terminated one is inactive for the dissociation. Unlike the (0001) surface which is more easily reduced, the (1010) surface is readily hydroxylated. Water formation and desorption results in surface oxygen depletion and Zn aggregation which lead to surface metallization, in accordance with the experimental observations. Our simulations show that...

Inorganic nanocrystals catalysts with a high proportion of high-energy surfaces can bring about high performance for catalysis and has been an important research topic in the past decades. Gamma alumina is one of the most important inorganic oxides used as solid acids or catalytic support for many more industrial catalysts. However, the preparation of gamma alumina mainly with high-energy external surfaces has never been reported because it has a complicated crystal structure. We demonstrate here in depth a new-type γ-alumina material from a systematic investigation, which is controllably synthesized as regular nanotubes with high-energy {111} facets as main external surfaces. The new-type material shows much better performance as acid catalyst or catalytic support for metals, as compared with common γ-alumina whose main exposed surface is stable {100} or {110} facets in irregular morphology. As an example, palladium loaded on the new-type γ-alumina is easily prepared in higher dispersion and unique elect...

Centrosymmetric (CS) nonmagnetic materials with hidden spin polarization induced by non-CS site symmetries and spin-orbit coupling are promising candidates for spintronic applications, in light of the zero net spin polarization and modulatable spin effects hidden in the local structures. There is, however, an open issue regarding the possible spin splitting induced by broken inversion symmetry at the sample surface. Here, we performed combinatorial experimental and theoretical studies on the potentially hidden spin polarization in 2H-MoTe2 and its mechanism. A large spin splitting of 236 meV and opposite spin polarizations up to 80% along out-of-plane direction (z axis) in K and K′ valleys were observed from both spin- and angle-resolved photoemission spectroscopy (spin-ARPES) and density functional theory (DFT). We further found from the DFT calculations that a medium dipole field mimicked the surface symmetry breaking in ARPES measurements induces negligible variation of spin polarization. Our study demonstrates the existence of the intrinsic hidden spin effects in 2H-MoTe2 and opens a way of utilizing these effects in spintronic devices.

A series of bifunctional metal-salen complexes bearing ionic liquid substituents were investigated as catalysts for the synthesis of cyclic carbonates from carbon dioxide (CO2) and epoxides using density functional theory (DFT) and energy span model. Detailed studies reveal that the three-step mechanism involving the ring-opening of propylene oxide (PO), CO2 insertion, and ring-closure to the cyclic carbonate is kinetically more favorable than the two-step mechanism. The effect of ionic liquids, epoxide substituents and metal center of the metal-salen complexes were explored. Amino functionalized ionic liquids substituents tethered to the salen ligand of the metal-salen complexes performed well. Epoxide substituents affect the cycloaddition mainly through the electronic effect and the substituent that lowers the negative charges of the ring carbon atom to be attacked favors the cycloaddition. When the salen ligand is fixed, the catalytic activity metal-salen complexes can be measured by the interaction between the oxygen atom (O) of epoxides and the central metal (M) and there is a linear relationship between the energy span and the M-O bond length, which can be used as a descriptor to screen CO2 conversion catalysts.

We established adsorption energy-property models using the properties of adsorbate atom and substrate metal atom that do not need first-principles or quantum mechanics calculations (non-QM based parameters) with machine learning (ML) methods of SVR, RFR and MLPR. The models produce adsorption energies close to the density functional theory calculated results for the 12 types of atoms on the 38 metal surfaces. Application of the models to predict the adsorption energies on binary alloys is also successful. The present work provides a means to evaluate adsorption energies with non-QM quantities and is helpful for catalyst screening.

Oxygen vacancies on transition metal oxide surfaces are catalytically very important. The stability, shape and replenishing process of the vacancies are critical to understanding reactions happening on the surfaces. In this paper we investigate the stability of various defective MoO3(0 1 0) surfaces and examine the influence of environmental oxygen on the stability as well as the active sites for the replenishing process. Our calculations reveal that the line oxygen defect along a (asymmetric oxygen) direction is thermodynamically most favorable at higher defect concentration whereas point defect surfaces are unfavorable. Under normal experimental conditions the perfect surface dominates the MoO3(0 1 0). We show that for stoichiometric surfaces of any oxides (AxOy) the formation energy per vacancy controls the favorable defect shape (line or point defects). Calculations indicate that O2 can dissociate readily on the surfaces that double vacancies share one Mo atom. The replenishing process of the oxygen vacancies through O2 dissociation most likely occurs on the double-vacancy containing one terminal and one asymmetrical oxygen vacancies.

Density functional theory (DFT) calculations were performed to elucidate the mechanism and the origin of the high enantioselectivity of the aza-Henry reaction of isatin-derived N-Boc ketimine catalyzed by a quinine-derived catalyst (QN). The C–C bond formation step is found to be both the rate-determining and the stereo-controlled step. The results revealed the important role of the phenolic OH group in pre-organizing the complex of nitromethane and QN and stabilizing the in situ-generated nitronate and protonated QN. Three possible activation modes for C–C bond formation involving different coordination patterns of catalyst and substrates were studied, and it was found that both the ion pair-hydrogen bonding mode and the Bronsted acid-hydrogen bonding mode are viable, with the latter slightly preferred for the real catalytic system. The calculated enantiomeric excess (ee) favouring the S enantiomer is in good agreement with the experimental result. The high reactivity and enantioselectivity can be ascribed to the cooperative role of the multiple non-covalent interactions, including classical and non-classical H bonding as well as anion⋯π interactions. These results also highlight the importance of the inclusion of dispersion correction for achieving a reasonable agreement between theory and experiment for the current reaction.

Pd/ZnO is a promising catalyst studied for methanol steam reforming (MSR) and the 1 : 1 PdZn alloy is demonstrated to be the active component. It is believed that MSR starts from methanol dehydrogenation to methoxy. Previous studies of methanol dehydrogenation on the ideal PdZn(111) surface show that methanol adsorbs weakly on the PdZn(111) surface and it is hard for methanol to transform into methoxy because of the high dehydrogenation barrier, indicating that the catalyst model is not appropriate for investigating the first step of MSR. Using the model derived from our recent kinetic Monte Carlo simulations, we examined the process CH3OH → CH3O → CH2O → CHO → CO. Compared with the ideal model, methanol adsorbs much more strongly and the barrier from CH3OH → CH3O is much lower on the kMC model. On the other hand, the C-H bond breaking of CH3O, CH2O and CHO becomes harder. We show that co-adsorbed water is important for refreshing the active sites. The present study shows that the first MSR step most likely takes place on three-fold hollow sites formed by Zn atoms, and the inhomogeneity of the PdZn alloy may exert significant influences on reactions.

The knowledge of surface composition and atomic arrangement is prerequisite for understanding of catalytic properties of an alloy catalyst. Gaining such knowledge is rather difficult, especially for those possessing surface segregation. Pd–Cu alloy is used in many fields and possesses surface segregation. In this paper kinetic Monte Carlo method is used to explore the surface composition and structure and to examine the effects of bulk composition and temperature on the surface segregation of Pd–Cu alloys. It is shown that the segregation basically completes within 900 s at 500 K. Below 900 K and within 20 min the enriched surface Cu atoms mainly come from the top five layers. For the first time we demonstrate that there exists a “bulk-inside flocking” or clustering phenomenon (the same component element congregates in bulk) in Pd–Cu alloys. Our results indicate that for alloys with higher Cu content there are small Pd ensembles like monomers, dimers and trimers with contiguous subsurface Pd atoms.

Two-monolayer-Zn covered Pd(1 1 1) annealed at (low) 500 K exhibits nice CO2 selectivity for CH3OH+H2O to CO2+H2, whereas CO is yielded exclusively when annealed at (high) 650 K. To unravel the reason behind the phenomenon, kinetic Monte Carlo (KMC) simulations were used to study the alloying process. It shows the low temperature annealing produces a multilayer 1:1 PdZn alloy, whereas the high temperature operation results in a Zn-lean multilayer alloy, not the previously assumed monolayer PdZn alloy on Pd. The geometry and electronic structures of the models derived from KMC simulation agrees with the relevant experiments. The low temperature sample is more active than the high temperature one for H2O dissociation, in line with the assumption that H2O dissociation controls CO2 selectivity. It is revealed that triple Zn ensembles which form three-fold hollow sites account for the activity for H2O dissociation.

The mechanism and origin of stereoselectivity of rhodium(II)-catalyzed cyclopropanation reactions with diazooxindole and styrene has been studied using density functional theory calculations. The catalyzed reactions by achiral Rh2(OAc)4 and chiral Rh2(S-PTTL)4 as well as the uncatalyzed model were comparatively studied. The computational results indicate that the cyclopropanation step in both Rh2(OAc)4 and Rh2(S-PTTL)4 models is a single concerted but asynchronous process. The nitrogen extrusion step is found to be the rate-limiting step of the catalytic cycle, whereas the cyclopropanation step is the stereoselectivity-determining step. The diastereomeric ratios (dr) and the enantiomeric excess (ee) values are successfully predicted, which are in good agreement with the experimental values. The high trans-diastereoselectivity might be governed by the π–π interactions between the syn indole ring in carbenoid ligand and the phenyl group in styrene, whereas the good enantioselectivity can be ascribed to the steric interaction between the phenyl ring in styrene and the phthalimido group in the catalyst as well as the aromatic interactions (π–π and CH–π) in the transition states. Additionally, the methodological study using different functionals demonstrated the importance of considering the dispersion interactions in the current reaction systems. This theoretical study will help in understanding the mechanism of the asymmetric cyclopropanations of olefins through carbene-transfer reactions.

Energetic materials are a special and important kind of substance. Impact sensitivity, which refers to the vulnerability to explosion under external stimuli, measures the safety and reliability of an energetic material and is a critical property. Various efforts have been made to rationalize the impact sensitivity of different types of energetic materials. Since a chemical explosion is a chemical reaction dominated phenomenon, a comprehensive understanding of such explosive processes requires detailed information of chemical bonding and molecular interaction. Quantum chemistry provides a modern theory of chemical bonding and computational quantum chemistry is a powerful tool to investigate chemical phenomena. Even at the very beginning of computational quantum chemistry, researchers in the field of energetic materials have begun to apply quantum chemistry to explosive properties. In this paper we review the quantum chemistry studies on impact sensitivity and examine various quantum chemistry derived parameters used to rationalize the impact sensitivity ordering of various energetic materials.

For the kinetic simulation of metal nanoparticles, we developed a self-consistent coordination-averaged energies for Au atoms based on energy properties of gold bulk phases. The energy barrier of the atom pairing change is proposed and holds for the microscopic reversibility principle. By applying the lattice kinetic Monte Carlo simulation on gold films, we found that the atomic diffusion of Au on the Au(111) surface undergoes a late transition state with an energy barrier of about 0.2 eV and a prefactor between 40~50 Å2/ps. This study also investigates the structural transition from spherical to faceted gold nanoparticles upon heating. The temperatures of structural transition are in agreement with the experimental melting temperatures of gold nanoparticles with diameters ranging from 2 nm to 8 nm.

MoO3 is an important catalytic material, and there exist controversial viewpoints about its surface structure, oxygen vacancy, and hydrogen adsorption, which are crucial for rationalizing the catal...

Metal-directed assembly of naphthalene-1,4,5,8-tetracarboxylic acid (NTA) with different transition-metal salts in the presence of ammonia results in a series of one-dimensional metal−naphthalenediimidato (M−NDI) coordination polymers with the formulas of {(Ag(NDI))(NH4)}n (P1), (Zn(NDI)(NH3)2)n (P2), (Cd(NDI)(NH3)2)n (P3), (Co(NDI)(NH3)2)n (P4) and (Ni(NDI)(NH3)2)n (P5), respectively. It is worthwhile to mention that the 1D straight-line NDI−Ag(I) coordination polymer P1 is formed stepwise from a dinuclear NDI−Ag(I) intermediate (Ag2(NDI)(NH3)2 )( 2AgNDI), where ammonia serves as a stabilizing reagent of Ag(I) ion and a weak base to remove the protons of NDIH2 simultaneously. Furthermore, P1 exhibits semiconducting properties in the solid state which may originate from its all-parallel-aligned packing structure (AAAA) which is different from the common ABAB packing mode for P2−P5 and 2AgNDI. In addition, theoretic computational studies as well as X-ray photoelectron spectrometer spectra on P1 and 2AgNDI have also been carried out.

We present kinetic Monte Carlo simulations of ethylene conversion to ethylidyne on Pd(1 1 1) and Pt(1 1 1) surfaces, on the basis of reaction enthalpies and barriers obtained from periodic density functional calculations. We considered three possible mechanisms encompassing four different intermediates, ethyl, vinyl, ethylidene, and vinylidene. Our simulations predict that the most plausible pathway on both surfaces is ethylene --> vinyl --> vinylidene --> ethylidyne. In contrast to earlier suggestions that the dehydrogenation to vinyl is rate-limiting on Pt(1 1 1), we found the hydrogenation of vinylidene to ethylidyne to be crucial on this surface. On Pd(1 1 1), the initial dehydrogenation of ethylene is rate-limiting. Hence, vinylidene species accumulate on Pt(1 1 1), while all intermediates on Pd(1 1 1) convert rapidly to ethylidyne without accumulation. The simulated apparent activation energies for the formation of ethylidyne on Pd(1 11 ), 94 kJ mol(-1), and on Pt(1 1 1), 65 kJ mol(-1), agree well with experimental results. (C) 2011 Elsevier Inc. All rights reserved.