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[Display omitted] • The hemilabile Me-Dalphos promotes oxidative addition step of aryl halides to AuI. • The alkene difunctionalization could prevail over cross-coupling for methanol. • The reactivity of different nucleophiles results in the final chemoselectivity. A computational mechanistic study of gold-catalyzed intermolecular alkene difunctionalization/cross-coupling of aryl iodides with methanol was studied. By calculating the corresponding initial oxidative addition step mediated by the related chelating (P,N) ligands, our results uncover the essential roles of hemilabile Me-Dalphos to promote the oxidative addition process by minimizing the distortion of substrate and catalyst. For the nucleophile methanol, by comparing the mechanism of intermolecular alkene difunctionalization versus cross-coupling, the C(sp2)–C(sp3) reductive elimination is found more favorable than the corresponding C(sp2)–O formation, which contributes to the exclusive intermolecular alkene oxyarylation product. Furthermore, the different reactivity and selectivity of other nucleophiles such as tosyl amine and 1,3,5-trimethoxybenzene were compared. This mechanistic understanding will provide valuable guidance for the further development and wider application of gold-catalyzed redox reactions in synthetic chemistry. [ABSTRACT FROM AUTHOR]

Density functional theory has been applied to the novel procedure-controlled enantioselectivity switch in the synthesis of chiral 2-oxazolidinone ( 3 ) through [3 + 2] cycloaddition between γ-hydroxy-α,β-unsaturated carbonyl compound ( 1 ) and isocyanate ( 2 ) catalyzed by a cinchona-alkaloid based aminothiourea catalyst. The study shows that three stages are involved in the whole process. In stage one, for Procedure A, 1 reacts with 2 to give carbamate intermediate. Then catalyst 4 is added. For Procedure B, catalyst 4 first activates 2 via quinuclidine N attacking isocyanate C. Then 1 is involved. In stage two, hydrogen is transferred from carbamate N to Ts O atom which is different from the quinuclidine N protonation mechanism. The last step is ring closure in which carbamate N attacks C atom of C C bond. From free energy profiles, the enantioselectivities of the reaction are determined by stage two. Further analysis shows that H-bond is the key in the procedure-controlled enantioselectivity switch. Different H-bonds (N A H A ⋯O A C and N B H B ⋯O A C in Procedure A vs N A H A ⋯O A C and N B H B ⋯O B S in Procedure B) lead to different relationships between thiourea and carbamate planes (vertical or parallel). In Procedure A, C C listing above carbamate plane is the favorable pathway to give R-3 . However, in Procedure B, C C listing behind carbamate plane is more favorable to generate S-3 . [ABSTRACT FROM AUTHOR]

[Display omitted] The mechanisms of the Rh(I)-catalyzed alkenylation reaction were investigated by density functional theory (DFT) calculations. Our results show that the C H activation of this reaction occurs through the metal hydride pathway rather than the general concerted metalation deprotonation (CMD) mechanism. The favorable metal–hydride pathway involves C H oxidative addition, alkyne migratory insertion into Rh H and C C reductive elimination. Moreover, the consecutive migratory insertion into the Rh H and C C reductive elimination is kinetically more favorable than the alkyne migratory insertion into Rh C and C H reductive elimination. The CMD pathway is kinetically unfavorable due to the considerably higher barrier of several elementary steps. The improved mechanistic understanding will enable design of novel couplings between hydrocarbons and C H bonds. [ABSTRACT FROM AUTHOR]

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]

Highlights: [•] Adsorption of a Pt atom on polyaromatic hydrocarbons is investigated. [•] The Pt–C charge transfer depends on the Pt–C bond lengths. [•] Dispersion and relativistic contribution are crucial for Pt–C DFT calculations. [•] SSB-D functional with ZORA is recommended for Pt/C calculations. [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]

Abstract: First-principles calculations based on density functional theory and the generalized gradient approximation have been used to study the C chemisorption and diffusion on the surface and in the subsurfaces of Ni(111). The threefold Hcp site is observed to be preferred by the C adsorption on Ni(111) surface while in the subsurfaces, the octahedral site is more energetically favorable than the tetrahedral site and all surface adsorption sites. The calculated binding energies have been compared with the previous experimental and theoretical results and good agreement is found. Minimum energy paths for the C diffusion between different adsorption sites are also investigated using the nudged elastic band method. It is predicted that if the C surface diffusion rate is higher than the production rate of C atoms during the growth of carbon nanofibers and the C concentration is low at the Ni surface, the generated C atoms are likely to diffuse on the catalyst surface predominantly because of the lowest energy barrier, while if the generated C production rate is higher and some adsorption sites are blocked by the accumulated carbon, the C atoms may diffuse both on the surface and in the subsurfaces simultaneously. [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]

• CH 4 direct dehydrogenation is preferred on Ni. • OH-assisted dehydrogenation of CH 4 is favored on Pt and Ni@Pt. • CO 2 direct dissociation is more favorable than H-assisted way on Ni. • H-assisted CO 2 dissociation is the dominant way on Pt and Ni@Pt. CO 2 reforming of methane (DRM) is a promising reaction for the carbon cycle in nature. Ni was found to be active in this process. However, single component Ni catalysts cannot meet the stability, activity and selectivity demands simultaneously. This paper presents a systematical density functional theory study to investigate the catalytic performance of Ni@Pt(1 1 1) core-shell surface compared with Ni(1 1 1) and Pt(1 1 1) in methane dry reforming. Two ways of O* and OH* assisted CH 4 dehydrogenation are considered in present work. CH 4 direct dissociation is more favored on Ni, while OH*-assisted CH 4 dehydrogenation is more competitive to proceed on Pt and Ni@Pt compared with direct way. Furthermore, Ni@Pt provides much less energy-demanding pathways for both CH and C oxidation, under the assistance of O* or OH*. Therefore, CH is much easier to be oxidized rather than decomposition into carbon on this surface, meanwhile, it is beneficial for carbon elimination and shows promising anti-carbon formation performance. Finally, free energy profiles are plotted at 1000 K and dominant reaction mechanisms of DRM conditions are proposed on three surfaces, respectively. On Ni(1 1 1), O* generated from CO 2 direct dissociation could provide dominant oxidant for CH* oxidation, while on Pt(1 1 1) and Ni@Pt, OH* originated from CO 2 H-assisted dissociation acted as the major oxidant for CH* oxidation. This work sheds some light on dominant reaction pathway and surface carbon formation, which could provide new mechanistic insight into CO 2 reforming methane on Ni-core/Pt-shell surface. [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]

Highlights • H 2 adsorption energies are very similar on different facets and K preadsorbed on hcp Co. • H atom adsorption was site and facet dependent on hcp Co. • H 2 dissociation energy barriers were negligible (0–0.07 eV) on clean hcp Co. • K has a slight inhibiting effect on the H atom adsorption and H 2 dissociation. • Different K species (K and KOH) exhibit similar effect on H 2 dissociation on hcp Co. Abstract Trace amounts of potassium (K) have a significant influence on the activity and selectivity of cobalt-based catalysts in Fischer–Tropsch synthesis (FTS), in which hydrogen adsorption and dissociation is one of the initial and most important steps. In this work, hydrogen adsorption and dissociation behavior on typical facets ((0001), (10–11), (10–12), (10–15) and (11–20)) of hcp Co with and without adsorbed K were systematically studied. H 2 molecular adsorption results showed that H 2 mainly adsorbed in the perpendicular mode and close to the state of free H 2. Different facets and pre-adsorbed K did not show obvious effects on the H 2 adsorption energy. Atomic hydrogen adsorption was site and facet dependent, but the maximum hydrogen adsorption energy on the different facets of hcp Co were similar (-2.64 to -2.67 eV) with the exception on the (11–20) facet where the adsorption energy was significantly lower (-2.44 eV). K had a slight destabilizing effect on the H atom adsorption on the former Co surfaces due to a very weak repulsive interaction between K and H atoms. The initial H 2 dissociation had negligible energy barriers (0–0.07 eV) on the clean surface of hcp Co, suggesting the direct dissociative adsorption of H 2. The energy barriers for H 2 dissociation are mainly caused by the approach of molecular H 2 towards the Co surface and the rotation of the H 2 molecule from the perpendicular mode to the parallel mode. The H 2 dissociation energy barriers increase by 0.02–0.17 eV after the pre-adsorption of K, indicating a slight inhibition of H 2 dissociation by K. However, the energy barriers for H 2 dissociation in the presence of K were also small (0.05–0.21 eV). This indicates that H 2 dissociates readily at typical Co-based FTS reaction temperatures (210–240 °C), both in the absence and presence of K. Different K species (K and KOH) exhibit similar effects on H 2 dissociation on hcp Co. The B 5 sites on the stepped facets, the preferred sites for K adsorption are not the most favorable site for H 2 dissociation, and K slightly hinders H 2 dissociation at the B 5 site of hcp Co. Graphical abstract Image, graphical abstract [ABSTRACT FROM AUTHOR]

Catalytic hydrolysis of ammonia borane has tremendous potential as an energy-efficient approach to supply hydrogen for energy vehicles and portable electronic devices. Herein, DFT calculation is first performed on electronic properties of Ni 2 P and Ni 5 P 4 nanocatalysts. It is found that more electrons are transferred from Ni to P for Ni 5 P 4 , indicating that Ni 5 P 4 may show superior performance based on the electron effect. Therefore, Ni 2 P and Ni 5 P 4 with high purity are synthesized by the phase-controlled thermal decomposition approach. Gratifyingly, the Ni 5 P 4 catalyst exhibits the as-expected better catalytic activity than that of Ni 2 P catalyst. It also shows low activation energy and good stability. Furthermore, the structures and morphologies of both catalysts are characterized by multi-techniques such as XRD, HRTEM and XPS. The better performance could be ascribed to the higher positive charge of Ni together with the stronger ensemble effect of P. The insights sheds new light on the design of efficient Ni P catalysts for hydrogen generation. [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] • DFT calculations to examine the mechanism for 2‑heptene isomerization. • Understanding the product and transition-state shape selectivity in BEA and MFI. • The effect of zeolite framework on the distribution of isomerization products. Isomerization of n -alkanes is industrially applied to improve the octane number of gasoline. The origin of shape selectivity and influence of micropore confinement in this reaction have not been fully understood. In this work, periodic DFT calculations have been performed to examine the mechanism for n -heptene isomerization in H-BEA and H-MFI. Three reaction pathways, including the protonated cyclopropane, edged-protonated cyclopropane, and alkyl shift mechanisms, have been examined. It is found the formation of smaller di-branched isomers is determined by product shape selectivity, but that of relatively bulky isomers is kinetically relevant and can be accounted for by transition-state shape selectivity. [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: Ni catalysts are widely used to catalyze ammonia decomposition. In this study, first-principles calculations are performed to investigate the preferred adsorption sites and the adsorption energies of NHx (x=0–3) and H, and the transition states, activation energies and rate constants of NH3 stepwise dehydrogenation and associative desorption of N on the stepped Ni(211) and the close-packed Ni(111) surfaces. The results show that the barrier of associative desorption of N, which is higher than those of NH3 stepwise dehydrogenation, on Ni(211) are 1.10eV higher than that on Ni(111), indicating that the associative desorption of N on Ni(211) is difficult to take place. Hence the strongly adsorbed N atoms would block some of the step sites of Ni(211). The N-blocking Ni(211) surface is constructed, and then NH3 decomposition on 2N–Ni(211) is investigated. The results indicate that Ni catalysts with too many or too few step sites, which can be associated with Ni particle sizes, show low ammonia decomposition activities. Therefore, different sized Ni-based catalysts are employed to catalyze ammonia decomposition, and TOFH2 as a function of Ni particle size is correlated. Finally, the structure sensitivity of ammonia decomposition over Ni catalysts is rationally interpreted. [Copyright &y& Elsevier]

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]

Abstract: First-principles calculations based on density functional theory (DFT) have been performed to study the adsorption and decomposition of NH3 on Ni(110). The adsorption sites, the adsorption energies, the transition states and the activation energies of the stepwise dehydrogenation of NH3 and the associative desorption of N are determined, and the zero point energy correction is included, which makes it possible to compute the rate constants of the elementary steps in NH3 decomposition. Combined DFT calculations and kinetic analysis at 350K indicate that the associative desorption of N has a reaction rate lower than NHx dehydrogenation and is therefore the rate determining step. The distinctly different rate constants over Ni(110), Ni(111) and Ni(211) imply that ammonia decomposition over Ni-based catalyst is a structure-sensitive reaction. [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]

In this contribution, we combine density functional theory (DFT) calculations, experimental kinetic study and DFT-assisted analysis to elucidate the impact of the interface of monolayer Pt on the Ni surface on catalytic performance of steam methane reforming including carbon formation on core-shell (Ni@Pt) catalysts and compare it with Ni and Pt catalysts. We demonstrate that core-shell structured Ni@Pt significantly lowers the carbon formation without sacrificing much the activity. The DFT results demonstrate that the metal identity, core shell structure and support have significant impacts on the reaction mechanisms. The direct methane activation is energetically favorable reaction pathway on Ni, while the OH* assisted methane activation is the favorable pathway on Pt and Ni@Pt catalysts, where methane activation is the rate-determining step on all catalysts. We unambiguously reveal that the core-shell Ni@Pt catalyst modified the surface Pt electron density and shifted d -band center away from Fermi level compared to Ni(1 1 1) and Pt(1 1 1). It results in a strong basic surface OH* which actively reacts with CH x and thus enhances carbon formation resistance. Above all, Ni-core/Pt-shell particle could decouple the activity and carbon resistance to keep the activity and reduce carbon formation simultaneously in methane steam reforming. In addition, by taking into account the activation of steam on the support, the effective activation energy estimated from DFT-assisted analysis is well consistent with the experimental value on the both Ni and Ni@Pt catalysts, which could shed some light on building a bridge between experimental work and DFT-assisted kinetic study. [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]