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Abstract: First-principles calculations based on density functional theory (DFT) have been used to investigate the reaction mechanism of dry methane reforming on Ni(111). The most energetically favorable adsorption configurations of the species involved in this process are identified and the transition states for all the possible elementary steps are explored by the dimer method. Then, the related thermodynamic properties at 973.15K are calculated by including the zero-point energy correction, thermal energy correction and entropic effect. It is found that CO2 dissociates via a direct pathway to produce CO and O dominantly, and atomic O is revealed to be the primary oxidant of CH x intermediates. Based on this information, two dominant reaction pathways are constructed as both the CH and C oxidation are found to be likely. The reaction network begins with the dissociation of CO2 and CH4, and then the generated CH and C are oxidized by atomic O to produce CHO and CO, followed by the CHO decomposition to finally generate CO and H2. As for these two reaction pathways, the oxidation step is predicted to determine the overall reaction rate under the current investigated conditions, while the CH4 dissociation is found to be the rate-limiting step at lower temperatures. [Copyright &y& Elsevier]

Abstract: First-principles calculations based on density functional theory and the generalized gradient approximation have been used to study the adsorption and dissociation of CH4 on Ni(100) surface. The favored adsorption sites of H, CH3, and CH4 are identified by considering the energy and stability of various binding sites. H atoms prefer the fourfold Hollow sites, while CH3 species favors the Bridge site with one of the C–H bonds pointing towards the neighbor Ni atom. When H and CH3 are coadsorbed on Ni(100) surface, several stable configurations are found, in which the atomic H and CH3 species are adsorbed at the Hollow and Bridge site, respectively, because of their little energetic difference. Through the electronic and vibrational calculations, the C–H–Ni three-center bond is regarded as the key factor determining the CH3 adsorption. The CH4 dissociation on Ni(100) surface is investigated with three different CH4 orientations considered. The energy barriers are calculated to be 0.61, 0.61 and 0.62eV, corresponding to the CH4 molecules orientated with one, two and three C–H bonds pointing towards the surface, respectively. All calculated activation energies have been corrected by including zero-point energy and dispersion energy, and are in good agreement with the experimental result (0.61±0.02eV). Because the energy barriers for the different reaction pathways take similar values, the CH4 orientation has a minor effect on the reactivity. [Copyright &y& Elsevier]

[Display omitted] • The electronic structure of V 2 O 3 upon single-atom doping is examined. • A weak Lewis acid-base interaction is found to occur on the pristine surface. • The first dehydrogenation step is identified as the rate-limiting step for PDH. • Mn 1 -V 2 O 3 is suggested to be a good catalyst candidate for PDH. Vanadium-oxide-based catalysts have recently been found very promising for the catalytic dehydrogenation of propane. In this work, self-consistent density functional theory calculations have been performed to examine how the electronic structure of the V 2 O 3 (0001) surface is modified by single-atom doping and how the catalytic properties can be tailored to propane dehydrogenation. The structural stability of single-atom-doped V 2 O 3 (0001) surfaces is assessed by comparing the adsorption energies of single atoms with the cohesive energies of bulk metals. A weak Lewis acid-base interaction is found to occur on the pristine surface, which can be strengthened and weakened by substitution of single atoms for V and O, respectively. On these two types of oxide surfaces, single atoms act as promoters and active sites. The first dehydrogenation step is identified as the rate-limiting step by microkinetic analysis. On all the single-atom-doped surfaces, the activation energy for water formation is higher than that for hydrogen recombination, implying that reduction of the oxide surfaces is difficult to take place during the course of the reaction. If a compromise between the catalytic activity and catalyst selectivity is made, Mn 1 -V 2 O 3 is suggested to be a good candidate as the catalyst for propane dehydrogenation. [ABSTRACT FROM AUTHOR]

Sub-nanometer-sized Cu 6 and Au 6 clusters are stably anchored on the oxygen-deficient anatase TiO 2 surface, where Cu 6 -(V O)-TiO 2 shows high catalytic activity and satisfactory selectivity toward MG. [Display omitted] • The size and structure of stable Cu and Au clusters on TiO 2 are determined. • Oxygen vacancies can stabilize sub-nanometer-sized metal clusters. • Ti 5c and Cuδ+/Auδ- ions are coordinated to reaction intermediates. • The activity of Cu 6 -(V O)-TiO 2 (1 0 1) shows strong temperature sensitivity. • Cu-TiO 2 has good catalytic performance for DMO hydrogenation and MG production. The electronic structures of Cu-TiO 2 and Au-TiO 2 and their catalytic behaviors in the hydrogenation of dimethyl oxalate (DMO) have been studied by the stochastic surface walking-global neural network potential method, density functional theory calculation, and microkinetic analysis. Calculated results indicate that metal clusters on the pristine and oxygen-deficient TiO 2 are mostly coordinated to O 2c ions, and the defective surface may provide additional oxygen vacancies for Cu 6 and Au 6 cluster anchoring. It turns out that the interfacial Ti 5c and Cuδ+/Auδ- ions provide adsorption and hydrogenation sites for the reaction intermediates with unsaturated O and C atoms, respectively. The turnover frequency for DMO consumption is much higher on Cu-TiO 2 than on Au-TiO 2 , Cu(1 1 1), and Cu(2 1 1) at 443.15 K and 20 bar of total pressure. Given the satisfactory methyl glycolate (MG) selectivity, the Cu-TiO 2 catalyst has the potential to act as an excellent catalyst for the selective MG production. [ABSTRACT FROM AUTHOR]

This work gives an insight into combined experimental and DFT study of water gas shift reaction on Ni catalysts at moderately elevated temperatures. The relative reactivity of surface adsorbed species O*, OH* and H* with CO* and their catalytic consequence in reaction mechanism and kinetics was studied. DFT investigation and microkinetic analysis pointed out that the favorable reaction pathway depends on the relative reactivity of O*, OH* and H* with CO* on the surface. It rationalizes the experimental observed changes in kinetics with hydrogen pressure. • Experimental and DFT study leads to WGS reaction mechanism insight on Ni catalyst. • It reveals dependency of the reaction mechanism and kinetics on hydrogen pressure. • Reaction pathway is dependent on relative reactivity of O*, OH* and H* with CO*. • DFT studies rationalize the experimental changes in kinetics with H 2 pressure. This paper presents a combined experimental and density functional theory study of the relative reactivity of surface species O*, OH*, and H* with CO* on nickel catalysts and their catalytic consequence in reaction mechanism and kinetics of water gas shift reaction. The kinetic study illustrates the hydrogen reaction order changes from 0.5 at relatively low hydrogen pressures to -1 at high hydrogen pressures. Detailed kinetic analysis indicated a hydrogen-induced change of the corresponding reaction pathway from hydrogen assisted CO activation to the redox mechanism with CO*+O* as a rate-determining step. The DFT investigation revealed that the surrounding surface H* atoms destabilize more significantly O* adsorption than H* adsorption, thus enhance more the reactivity of O* than H* towards reaction with CO* at high H* coverage. This kinetic study provides an insightful depiction for the future study of CO activation on other transition metals and the catalyst development for WGS reaction. [ABSTRACT FROM AUTHOR]

• The "dimethylcyclopropane" pathway is dominant for 2-pentene isomerization. • The ring-opening step is the rate-determining step for the isomerization reaction. • Van der Waals interactions would change the scaling relations in zeolite catalysis. Periodic density functional theory (DFT) calculations have been performed to examine the monomolecular reaction mechanism for 2-pentene skeletal isomerization catalyzed by acidic zeolite Beta, Mordenite, and ZSM-5. The use of periodic models allows consideration and analysis of zeolite steric constraints that occur within zeolite microspores. Three different reaction pathways, the "dimethylcyclopropane" (DMCP), methyl shift, and ethyl shift mechanisms, have been considered. The DMCP mechanism which includes rearrangement of protonated cyclopropane is proposed as the dominant reaction pathway, and the ring-opening step determines the overall reaction rate. Comparison of the effective energy barriers for 2-pentene isomerization over the three different zeolites reveals that large 12-ring channels of Beta and MOR have little steric hindrance effect on 2-pentene isomerization while small 10-ring of ZSM-5 significantly increases the reaction activation energy. Calculated results also indicate that the adsorption heat of ammonia is a good descriptor for the reactivity of zeolites without taking into account long-range dispersive forces. In contrast, linear scaling relations cannot be obtained by using the BEEF-vdW functional because van der Waals interactions between zeolites framework and guest molecules affects the energetics of the isomerization reaction and changes the transition state energy scaling relation in zeolite catalysis. [ABSTRACT FROM AUTHOR]

• The reducibility and structural stability of LaMO 3 (M = Sc - Cu) are examined. • The first four LaMO 3 perovskites have very high oxygen vacancy formation energies. • The maximum possible oxygen deficiency in LaMO 3 (M = Mn - Ni) is 0.5. • LaCuO 3 can lose one lattice oxygen atom per formula unit before it is deactivated. Periodic density functional theory calculations have been performed to examine the effect of oxygen deficiency on the structural stability of Lanthanum-based perovskites (LaMO 3), where on-site Coulomb interactions have been addressed by an additional Hubbard-type term. Calculated results indicate that with the exception of LaFeO 3 , the oxygen vacancy formation energy (Δ E f o r m a t i o n , v a c ) of LaMO 3 (M = Sc - Cu) becomes less positive when moving across the first transition metal period. The first four LaMO 3 perovskites have very high oxygen vacancy formation energies and can hardly be reduced under mild conditions, while the other five perovskites exhibit a much greater reducibility. During the formation of the first oxygen vacancy in LaMO 3 (M = Mn - Cu), the nearest neighbor transition-metal cations serve as the primary acceptors of the electrons left behind. As oxygen atoms are further removed, square-based pyramidal and tetrahedral coordination geometries appear successively, and an abrupt increase in Δ E f o r m a t i o n , v a c is observed at a specific oxygen deficiency (δ), which defines the maximum possible δ in the perovskite structures. Under this definition, the M3+ cations (M = Mn - Ni) can be possibly reduced to M2+ while LaCuO 3 may lose at most one lattice oxygen atom per formula unit before it is deactivated. [ABSTRACT FROM AUTHOR]

Pd nanoparticles encaged within an amine-functionalized metal-organic framework (MOF), Pd@NH 2 -UiO-66, was successfully prepared via one pot direct construction of the MOF framework, cooperative in situ metal precursor incorporation followed by on-site moderate reduction process. Because of its abundant of nanocages accessible through small pore windows, as well as excellent coordination capability of metal ions sites from the amine groups within the NH 2 -UiO-66 matrix, the Pd nanoparticles were homogeneously confined within its cavities. Intriguingly, the prepared Pd@NH 2 -UiO-66 exhibits a high catalytic activity and exclusive selectivity in the liquid-phase hydrogenation of 2,3,5-trimethylbenzoquinone (TMBQ) to 2,3,5-trimethylhydroquinone (TMHQ), a key vitamin-E intermediate in a short period under relatively mild reaction conditions. Additionally, this catalyst was recycled up to 8 times without significant loss in both activity and selectivity. Furthermore, reaction mechanism was investigated using dispersion corrected density functional theory calculations, suggesting that the superior performance of Pd@NH 2 -UiO-66 could be ascribed to the cooperation between the Pd nanoparticle and the amine-functionalized UiO-66. This MOF-based composite shows great potential as heterogeneous catalyst for the catalytic hydrogenation reactions due to its high stability, excellent catalytic properties, and simple preparation. [ABSTRACT FROM AUTHOR]

[Display omitted] • Substitution of transition metals for Cr increases the acidity of the adjacent O. • Linear scaling relations are established to identify the PDH activity descriptor. • High propylene selectivity of the M 1 -Cr 2 O 3 catalysts is achieved. • Cu 1 -Cr 2 O 3 is predicted to be the best catalyst for PDH among the 13 doped Cr 2 O 3. The catalytic behavior of M 1 -Cr 2 O 3 (M = Mn-Cu, Ru-Ag, and Os-Au) in propane dehydrogenation (PDH) has been studied by employing microkinetic modeling combined with results from periodic DFT + U calculations. Calculated results indicate that most of the single atoms concerned can be stably present on the Cr 2 O 3 surface. The adsorption energy calculations and Bader charge analysis demonstrate that the acidity of the O sites adjacent to the M sites would be enhanced upon doping, which in turn strengthens the atomic H adsorption and the co-adsorption of various PDH species. The surface H formation energy is identified as the reactivity descriptor for PDH over the M 1 -Cr 2 O 3 catalysts, and a volcano curve of the PDH activity is obtained. By calculating the difference between the propylene dehydrogenation and desorption barriers, it is found that some M 1 -Cr 2 O 3 catalysts show improved selectivity towards propylene, as compared to Cr 2 O 3. Comparison between the formation barriers of H 2 and H 2 O reveals that single-atom doping has no apparent negative effect on the catalytic stability of the Cr 2 O 3 surface. The Cu 1 -Cr 2 O 3 catalyst is finally identified as the most promising catalyst for PDH among the 13 M 1 -Cr 2 O 3 catalyst candidates, considering the catalytic activity, selectivity, stability, and cost. [ABSTRACT FROM AUTHOR]

[Display omitted] • Fe and K were introduced into Pt/MOR catalysts to modulate the reactants adsorption in CO-PROX. • 1Pt0.1 K/Fe-MOR achieves 100% CO conversion and 60–70% CO 2 selectivity within 130–200 °C. • Fe improves the CO conversion by providing more oxygen vacancies to activate O 2. • K promotes the CO 2 selectivity by enhancing CO adsorption and weakening H 2 adsorption on Pt. Developing efficient and stable catalysts for preferential oxidation of CO (CO-PROX) within a wide temperature window is significant for the industrial hydrogen resource purification process. Herein, dual promoters of Fe and K were deliberately introduced to the mordenite supported Pt catalyst for optimizing the adsorption behaviors of reactants in CO-PROX. The optimal 1Pt0.1 K/Fe-MOR catalyst can achieve 100% CO conversion and 60–70% CO 2 selectivity (the ratio of CO/O 2 is 1:1) under the realistic application temperature range (130–200 °C), and remains catalytically stable during 65 h testing at 140 °C. A combination of detailed characterizations and density functional theory (DFT) simulations show that Fe species can avoid the co-adsorption of O 2 on the Pt sites by providing more oxygen vacancy to activate O 2 , while K species will further enhance the adsorption of CO and repulse the adsorption of H 2 on Pt surface. Therefore, the optimized adsorption of CO, O 2 and H 2 results in a total CO conversion and high CO 2 selectivity in high temperature range. [ABSTRACT FROM AUTHOR]

Shaped metal particles are known to possess distinct catalytic properties, which is often attributed to the catalytic activities of different particle facets. In this contribution, propane dehydrogenation on Pt particles of different shapes is investigated by a combination of experiments and DFT calculations. The selectivity toward propylene and catalyst stability in propane dehydrogenation can be enhanced by shaping Pt nanoparticles under industrially relevant conditions. Octahedral particles (12.0 nm) dominated by the Pt(1 1 1) surface have higher selectivity toward propylene production and better stability than cubic particles (11.5 nm) that are dominated by the Pt(1 0 0) surface. Combined experiments and DFT calculations suggest that the weakened binding strength of propylene and increased energy barrier for the C–H bond cleavage in propylene dehydrogenation on Pt(1 1 1) compared to Pt(1 0 0) and Pt(2 1 1) contribute to the higher selectivity toward propylene by lowering the formation possibility of the deeply dehydrogenated intermediates. When coke is formed on the Pt surface, the d -band of surrounding Pt atoms is shifted farther below the Fermi level, leading to the deactivation of Pt catalyst. Our DFT calculations provide a rational interpretation of the experimental observations regarding the shape effects on propane dehydrogenation. [ABSTRACT FROM AUTHOR]

Abstract: Ammonia decomposition on transition metal surfaces is of great importance in energy and environmental industries. With the aim to obtain a systematic knowledge about the reaction mechanism of NH3 decomposition on the close-packed surfaces of the 3d-late transition metals, we perform first-principles calculations to determine the preferred adsorption sites and the adsorption energies of NH x (x =0–3) and H, and identify the transition states of the NH3 stepwise dehydrogenation reactions and the N recombination reactions on the close-packed Fe(110), Co(111) and Ni(111) surfaces. The results show that the calculated adsorption energies and activated energies mainly depend on the d-band center of metal surfaces. Barrier decomposition analysis reveals that the interaction among binding species in transition states will increase the energy barrier while the bonding to the surface of the species in the initial states and the transition states will decrease the energy barrier. Moreover, a linear relationship, known as the Brϕnsted–Evans–Polanyi relation, also exists between the activation energy of the N recombination reaction and the adsorption energy of N on the close-packed surfaces of the 3d-late transition metals. [Copyright &y& Elsevier]

We successfully realized the directional construction of Pt-Mn 2 O 3 interfacial sites (by the combination of in-situ doping and impregnation methods) to boost selective oxidation of ethylene glycol under mild conditions. It is found that the pre-distribution of Mn 2 O 3 inside support unexpectedly induced the formation of Pt-Mn 2 O 3 interfacial active sites with strong electron coupling effect, leading to an unprecedented glycolic acid oxidation activity (turnover frequency: 3196.9 h−1) and glycolic acid yield (86.4 %). • Enhanced catalytic performance of ethylene glycol oxidation was achieved. • Strong electron coupling effect was revealed in the Pt-Mn interface. • Quantitative analysis of the intrinsic active sites was performed. • The promotion role of Pt-Mn interfacial on reaction mechanism was correlated. Rational design of desirable active sites is still a grand challenge for the efficient conversion of polyols to value-added products. Herein, we successfully constructed the Pt-Mn 2 O 3 interfacial sites rather than Pt-MnO x solid solution to boost selective oxidation of ethylene glycol to glycolic acid under mild conditions. X-ray absorption spectroscopy and high-resolution transmission electron microscope revealed that the pre-distribution of Mn 2 O 3 inside support unexpectedly induced the formation of Pt-Mn 2 O 3 interfacial active sites with strong electron coupling effect, leading to an unprecedented catalytic activity (turnover frequency: 3196.9 h−1) and glycolic acid yield (86.4 %). In addition, quantitative analysis of the intrinsic active sites was performed, and a "volcano-shape" relationship was established between initial reaction rate and Pt/Mn ratio. Moreover, the structure-dependent reaction kinetics and density functional theory calculation revealed that the synergistic effect between the Mn 2 O 3 redox cycle and Pt promotes the adsorption of ethylene glycol and the activation of C H bond, resulting in the lower activation energy of ethylene glycol oxidation. The outcome of this work offers a promising avenue for the direct construction of efficient Pt-based catalysts with desired active sites. [ABSTRACT FROM AUTHOR]

• High selectivity of core-shell alloy catalysts for propane dehydrogenation. • Linear scaling relations are established to identify the descriptor. • Microkinetic modeling is carried out to obtain turnover frequency. • Co@Pt is the best catalyst by making a compromise between activity and selectivity. Microkinetic analysis combined with the results obtained from density functional theory calculations has been performed to examine the catalytic activity and selectivity of Pt-based core-shell alloy catalysts for propane dehydrogenation. Calculated results indicate that substitution of 11 late transition metals for the core region of Pt nanoparticles would significantly modify the electronic structure of the surface Pt atoms through the strain effect and charge transfer. The core-shell catalysts are found to have less negative propylene adsorption energies and higher activation energies for the dehydrogenation reactions than Pt, thus giving rise to a lower catalytic activity and a higher selectivity toward propylene. Linear chemisorption energy and transition state energy scaling relations hold very well in the present work, and the adsorption energy of propylene is identified to be a good descriptor to represent the overall kinetics. The scaling relations also suggest that a higher catalyst selectivity toward propylene can only be achieved at the expense of a lower catalytic activity for propane dehydrogenation. If a compromise is made between catalytic activity and catalyst selectivity, Co@Pt is proposed to be the best core-shell catalyst for propane dehydrogenation. [ABSTRACT FROM AUTHOR]