Synergistic Functionality of Dopants and Defects in Co-Phthalocyanine/B-CN Z-Scheme Photocatalysts for Promoting Photocatalytic CO2 Reduction Reactions.

The realization of solar-light-driven CO2  reduction reactions (CO2 RR) is essential for the commercial development of renewable energy modules and the reduction of global CO2 emissions. Combining experimental measurements and theoretical calculations, to introduce boron dopants and nitrogen defects in graphitic carbon nitride (g-C3 N4 ), sodium borohydride is simply calcined with the mixture of g-C3 N4 (CN), followed by the introduction of ultrathin Co phthalocyanine through phosphate groups. By strengthening H-bonding interactions, the resultant CoPc/P-BNDCN nanocomposite showed excellent photocatalytic CO2 reduction activity, releasing 197.76 and 130.32 µmol h-1  g-1 CO and CH4 , respectively, and conveying an unprecedented 10-26-time improvement under visible-light irradiation. The substantial tuning is performed towards the conduction and valance band locations by B-dopants and N-defects to modulate the band structure for significantly accelerated CO2 RR. Through the use of ultrathin metal phthalocyanine assemblies that have a lot of single-atom sites, this work demonstrates a sustainable approach for achieving effective photocatalytic CO2 activation. More importantly, the excellent photoactivity is attributed to the fast charge separation via Z-scheme transfer mechanism formed by the universally facile strategy of dimension-matched ultrathin (≈4 nm) metal phthalocyanine-assisted nanocomposites.

Hydrogen-Bond-Donor-Directed Switching of Enantioselectivity in the Vinylogous Aldol-Cyclization Cascade Reaction of Prostereogenic 3-Alkylidene Oxindoles with Isatins and o-Quinones.

In this study, we reported a hydrogen-bond-donor-directed enantiodivergent vinylogous aldol-cyclization cascade reaction of 3-alkylidene oxindoles with isatins and o-quinones. Both enantiomers can be prepared by thiourea or squaramide cinchona alkaloid bifunctional organocatalysts with the same quinine scaffold. Kinetic study data provided the possible reaction mechanism for the vinylogous aldol-cyclization cascade reaction. The DFT calculation data showed the geometry of the generated dienolates from pronucleophiles dominated the observed switch of enantioselectivity.

Enantioselective Organocatalytic Three-Component Vinylogous Michael/Aldol Tandem Reaction among 3-Alkylidene oxindoles, Methyleneindolinones, and Aldehydes.

We reported a one-pot enantioselective three-component vinylogous Michael/aldol tandem reaction of prochiral 3-alkylidene oxindoles with methyleneindolinones and aldehydes using bifunctional organocatalysts. A variety of enantioenriched 3,3-disubstituted oxindoles 3 and spirolactones 4 were generated in moderate yields (up to 78%) with high stereoselectivities (up to >20:1 dr, >99% ee). Intriguingly, we observed that the aldol reaction with paraformaldehyde generates 3,3-disubstituted oxindoles 3 bearing a hydroxymethyl group, while the reaction with aliphatic aldehydes generates spirolactones 4.

Single Pt atom supported on penta-graphene as an efficient catalyst for CO oxidation.

Single-atom catalysts (SACs) have gained special attention due to their unique performances in CO oxidation. Herein, a single Pt atom supported on penta-graphene (Pt/PG) was explored as a SAC towards CO oxidation by applying spin-polarized first-principles calculations. The possible mechanisms for CO oxidation by O2 on Pt/PG, including two traditional mechanisms, Eley-Rideal (ER) and Langmuir-Hinshelwood (LH), and a new tri-molecular Eley-Rideal (TER) mechanism, are illustrated. Our computations revealed that the direct ER pathway (O2 + CO → O + CO2) and TER pathway (2CO + O2→ OCO-OCO → 2CO2) with activation energies of 0.11-0.20 eV and 0.35 eV for the rate-limiting step, respectively, were more preferable than the LH pathway (0.45 eV). The TER pathway was proposed as the most favored pathway since the adsorption of CO was much stronger than the adsorption of O2, allowing for the ER pathway to be restrained. This finding demonstrated that Pt/PG as a single-atom catalyst exhibited an excellent catalytic activity toward CO oxidation and provided a new strategy for the design of single-atom catalysts based on penta-graphene.

Computational Study on the Mechanisms and Rate Constants for the O(3P,1D) + OCS Reactions.

The mechanisms and kinetics of O(3P,1D) + OCS(X1Σ+) reactions have been studied by the high-level G2M(CC2) and CCSD(T)/6-311+G(3df)//B3LYP/6-311+G(3df) methods in conjunction with the transition-state theory and variational Rice-Ramsperger-Kassel-Marcus theory calculations. The result shows that the triplet surface proceeds directly by abstraction and substitution channels to produce SO(3P) + CO(X1Σ+) and S(3P) + CO2(X1 Σg+) by passing the barriers of 7.6 and 9.1 kcal·mol-1 at the G2M(CC2)//B3LYP/6-311+G(3df) level, respectively, while two stable intermediates, LM1 (OSCO1) and LM2 (SC(O)O1), are formed barrierlessly from O(1D) + OCS(X1Σ+) in the singlet surface, which lie at -40.5 and -50.1 kcal·mol-1 relative to O(3P) + OCS(X1Σ+) reactants and decompose to CO(X1Σ+) + SO(a1Δ) and S(1D) + CO2(X1Σg+). LM1 and LM2 may also be produced by singlet-triplet surface crossings via MSX1 and MSX2; the predicted total rate constant for the O(3P) + OCS(X1Σ+) reaction including the crossings, 9.2 × 10-11 exp(-5.18 kcal·mol-1/RT) cm3 molecule-1 s-1, is in good agreement with available experimental data. The branching ratio of the CO2 product channel, 0.22-0.32, between 1200 and 1600 K, is also in excellent agreement with the value of 0.2-0.3 measured by Isshiki et al. (J. Phys. Chem. A. 2003, 107, 2464).

Monitoring the Effect of Different Metal Centers in Metal-Organic Frameworks and Their Adsorption of Aromatic Molecules using Experimental and Simulation Studies.

In this study, the adsorption behavior of different metal centers in analogous M-1,4-NDC frameworks (1,4-NDC=1,4-naphthalenedicarboxylate) towards guest molecules through simulation studies and experimental studies is reported. Simulation studies showed that the adsorption behavior of analogous M-1,4-NDC is affected by the atomic radius of the metal center, which was found to be in agreement with the experimental studies.

Catalytic CO oxidation on B-doped and BN co-doped penta-graphene: a computational study.

The catalytic reaction of carbon monoxide oxidation on boron-doped and boron-nitrogen co-doped penta-graphene materials has been systematically studied by utilizing spin-polarized density functional theory (DFT) calculations. Various pathways including the Eley-Rideal (ER), Langmuir-Hinshelwood (LH), and tri-molecular Eley-Rideal (TER) mechanisms were considered in which the TER mechanism is a newly proposed reaction mechanism for CO oxidation. According to the calculation results, the ER, LH and TER mechanisms of CO oxidation can occur and compete with each other because of the related small overall reaction energy barriers (0.11-0.35 eV for the ER mechanism, 0.16-0.17 eV for the LH mechanism, and no activation energy for the TER mechanism). Our study helps to understand the various pathways for the CO oxidation process and suggests that both B-doped and BN co-doped penta-graphene sheets may serve as effective metal-free catalysts for low-temperature CO oxidation.

Nitrogen-doped C60 as a robust catalyst for CO oxidation.

The O2 activation and CO oxidation on nitrogen-doped C59 N fullerene are investigated using first-principles calculations. The calculations indicate that the C59 N fullerene is able to activate O2 molecules resulting in the formation of superoxide species ( O2-) both kinetically and thermodynamically. The active superoxide can further react with CO to form CO2 via the Eley-Rideal mechanism by passing a stepwise reaction barrier of only 0.20 eV. Ab initio molecular dynamics (AIMD) simulation is carried out to evidence the feasibility of the Eley-Rideal mechanism. In addition, the second CO oxidation takes place with the remaining atomic O without any activation energy barrier. The full catalytic reaction cycles can occur energetically favorable and suggest a two-step Eley-Rideal mechanism for CO oxidation with O2 catalyzed by the C59 N fullerene. The catalytic properties of high percentage nitrogen-doped fullerene (C48 N12 ) is also examined. This work contributes to designing higher effective carbon-based materials catalysts by a dependable theoretical insight into the catalytic properties of the nitrogen-doped fullerene. © 2017 Wiley Periodicals, Inc.

Nitrogen-doped carbon nanotube as a potential metal-free catalyst for CO oxidation.

We elucidate the possibility of nitrogen-doped carbon nanotube as a robust catalyst for CO oxidation. We have performed first-principles calculations considering the spin-polarization effect to demonstrate the reaction of CO oxidation catalyzed by the nitrogen-doped carbon nanotube. The calculations show that O2 species can be partially reduced with charge transfer from the nitrogen-doped carbon nanotube and directly chemisorbed on the C-N sites of the nitrogen-doped carbon nanotube. The partially reduced O2 species at the C-N sites can further directly react with a CO molecule via the Eley-Rideal mechanism with the barriers of 0.45-0.58 eV for the different diameter of nanotube. Ab initio molecular dynamics (AIMD) simulations were performed and showed that the oxidation of CO occurs by the Eley-Rideal mechanism. The relationship between the curvature and reactivity of the nitrogen doped carbon nanotube was also unraveled. It appears that the barrier height of the rate-limiting step depends on the curvature of the nitrogen-doped carbon nanotube in the trend of (3,3)-NCNT < (4,4)-NCNT < (5,5)-NCNT (decreases with increased curvature). Using this relationship, we can predict the barriers for other N-doped carbon nanotubes with different tube diameters. Our results reveal that the nitrogen doped carbon nanomaterials can be a good, low-cost, and metal-free catalyst for CO oxidation.

The CO oxidation mechanism on the W(111) surface and the W helical nanowire investigated by the density functional theory calculation.

Two CO oxidation reactions (CO + O2 → CO2 + O and CO + O → CO2) were considered in the Eley-Rideal (ER) reaction mechanism. These oxidation processes on the W(111) surface and the W helical nanowire were investigated by the density functional theory (DFT) calculation. The stable adsorption sites of O2 and O as well as their adsorption energies were obtained first. In order to understand the catalytic properties of the W helical nanowire, the Fukui function and local density of state (LDOS) profiles were determined. The nudged elastic band (NEB) method was applied to locate transition states and minimum energy pathways (MEPs) of CO oxidation processes on the W helical nanowire and on the W(111) surface. In this study, we have demonstrated that the catalytic ability of the W helical nanowire is superior to that of the W(111) surface for CO oxidation.

To Transfer or Not to Transfer? Development of a Dinitrosyl Iron Complex as a Nitroxyl Donor for the Nitroxylation of an Fe(III) -Porphyrin Center.

A positive myocardial inotropic effect achieved using HNO/NO(-) , compared with NO⋅, triggered attempts to explore novel nitroxyl donors for use in clinical applications in vascular and myocardial pharmacology. To develop M-NO complexes for nitroxyl chemistry and biology, modulation of direct nitroxyl-transfer reactivity of dinitrosyl iron complexes (DNICs) is investigated in this study using a Fe(III) -porphyrin complex and proteins as a specific probe. Stable dinuclear {Fe(NO)2 }(9) DNIC [Fe(µ-(Me) Pyr)(NO)2 ]2 was discovered as a potent nitroxyl donor for nitroxylation of Fe(III) -heme centers through an associative mechanism. Beyond the efficient nitroxyl transfer, transformation of DNICs into a chemical biology probe for nitroxyl and for pharmaceutical applications demands further efforts using in vitro/in vivo studies.

Promoting ethylene epoxidation on gold nanoclusters: self and CO induced O2 activation.

We have investigated the epoxidation of ethylene heterogeneously catalyzed by small gold nanoclusters based on density functional theory calculations. A promising trimolecular Langmuir-Hinshelwood mechanism via co-adsorbed ethylene- and CO-assisted reaction is addressed which provides significant insights into the fundamental catalytic mechanism for ethylene oxidation on small Au nanoclusters. O2 activation is found to be a key step for accelerating ethylene oxidation. Especially, the coadsorbed neighboring CO is found to be more robust for promoting the activation of the O-O bond, resulting in the formation of epoxide and CO2 due to the barrierless process. The new CO-promoted oxidation mechanism has also been clarified by the ab initio MD simulations.

Hydrogen generation by the reaction of H2O with Al2O3-based materials: a computational analysis.

The mechanisms for H2O adsorption on γ-Al2O3(110) surface were investigated to illustrate the influence of oxide modifiers on the hydrogen generation reaction. Periodic density functional theory (DFT) calculations with the projected augmented wave (PAW) approach were carried out to study the adsorption of H2O, OH, O and H species, as well as the reaction mechanisms of H2O splitting and H2 generation. Their corresponding structures and adsorption energies are also reported. The calculation results show that H2O, OH, O and H are preferably bound at Al(I)-top, Al(III)-bridge, Al(I,II)-bridge and Al(III)-bridge sites with adsorption energies of -0.42, -5.01, -8.70 and -2.38 eV, respectively. The potential energy profiles for water splitting and hydrogen generation on the γ-Al2O3(110) surface are mapped out. We find that hydrogen generation on the surface occurs via two processes, namely, H2O dehydrogenation and direct H2 generation with an overall exothermicity of 2.24 eV. The nonexistence of intrinsic transition-state barriers and the high exothermicity for the reaction of H2O(g) + γ-Al2O3(110) → O(ads)/γ-Al2O3(110) + H2(g) result in rapid H2 generation. The stepwise H2 generation mechanism of adsorption on the γ-Al2O3(110) surface was also demonstrated using first-principles molecular dynamics simulations. In addition, the nature of the interaction between the adsorbate and the surface during the reaction was also analyzed by the local density of states and by Bader charge calculations.

Adsorption and Reaction of C2H4 and O2 on a Nanosized Gold Cluster: A Computational Study.

We have investigated the adsorption and reaction mechanisms of C2H4 and O2 catalyzed by a Au38 nanoparticle based on periodic density-functional theory (DFT) calculations. The configurations of the adsorption of C2H4/Au38, O2/Au38, and O/Au38 as well as the coadsorption of C2H4-O2/Au38 were predicted. The calculation results show that C2H4, O2, and O are preferably bound at top (T), bridge (B), and hexagonal (h) sites with adsorption energies of -0.66, -0.99, and -3.93 eV, respectively. The detailed reaction mechanisms for ethylene epoxidation on the Au38 nanoparticle has been illustrated using the nudged elastic band (NEB) method. The oxidation process takes place via the Langmuir-Hinshelwood (LH) mechanism to generate ethylene oxide and acetaldehyde. The overall reaction of C2H4 + O2 + Au38 → ethylene oxide + O/Au38 is exothermic by 2.20-2.40 eV whereas those are 3.03-3.08 eV for the production of acetaldehyde and O/Au38. The nature of the interaction between the adsorbate and gold nanocluster has been analyzed by the detailed electronic local density of states (LDOS) to understand the high catalytic activity of the gold nanoclusters.

Computational study of the kinetics and mechanisms for the HCO + O3 reaction.

The mechanisms of radical-molecule reactions between HCO (formyl radical) and O3 (ozone) have been investigated by using BH&HLYP and QCISD methods with the 6-311++G(3df,2p) basis set. The energetics have been refined with CCSD(T) and QCISD(T) theoretical approaches with the same basis set based on the geometries calculated at the QCISD method. The intermediates of hydrogen-bonded complexes and the critical transition states are also examined with the multireference methods. Two possible reaction pathways containing hydrogen-abstraction and association-elimination processes for the interaction of HCO with O3 are proposed. Both reaction mechanisms can occur via the prereactive hydrogen-bonded complex, O3-HCO, with 2.45 kcal/mol stability at the CCSD(T) approach with respect to the reactants; even so, the hydrogen-abstraction mechanism exhibits a lower energy barrier. The rate constants for both processes are also predicted. The total rate constant at 298 K is calculated to be in close agreement with the experimental value of 8.3 × 10(-13) cm(3) molecule(-1) s(-1).

Density function theory study on adsorption and dissociation of H2O on Pd nanowire.

The adsorption and dissociation of H2O in Pd nanowire have been investigated by the density functional theory (DFT) studies. First, we construct Pd nanowire by basin-hopping method and use DFT calculation to find the ground state of Pd nanowire, and put the H2O molecular on different adsorption sites and the H2O molecule is found to preferentially absorb on a Top (T) site. The H2O molecule lies parallel to the Pd nanowire surface, while the O atom is bound at a Top site. We also calculate the partial density of state (PDOS) and election density difference. In addition, our calculated results demonstrate that the bonding between H2O and Pd nanowire is contributed by d orbitals of Pd nanowire and p orbitals of O atom. The nudged elastic band (NEB) method is applied to locate transition states and minimum energy pathways (MEP), and we discuss the dissociation behavior of the side-on H2O molecules on the top site of hexagonal and tetragonal planes, respectively.

The deformation mechanism of Ni-Ta bulk metallic glasses after tensile: molecular dynamics study.

The mechanical properties of Ni-Ta crystallizationand binary bulk metallic glasses (BMG) were investigated for this study at the nanoscale. First, the Ta9Ni3 crystals are formed by space group, and structures with different ratios (Ta1Ni1, BTa8Ni4, BTa9Ni3, BTa7Ni5) were put into unit cell randomly. The optimizations of BMG structures are performed by Density functional theory (DFT) calculation to find the stable amorphous structures and corresponding energy. The FMM is utilized to obtain the suitable parameters of tight-binding potential bystable amorphous structures and corresponding energies. Finally, we employ molecular dynamics (MD) simulation to study mechanical properties of Ni/Ta crystallization and BMG, such as atomistic stress-strain, plastic and elastic deformation, and elastic modulus.

Density function theory study of the adsorption and dissociation of carbon monoxide on tungsten nanoparticles.

The adsorption and dissociation properties of carbon monoxide (CO) molecule on tungsten W(n) (n = 10-15) nanoparticles have been investigated by density-functional theory (DFT) calculations. The lowest-energy structures for W(n) (n = 10-15) nanoparticles are found by the basin-hopping method and big-bang method with the modified tight-binding many-body potential. We calculated the corresponding adsorption energies, C-O bond lengths and dissociation barriers for adsorption of CO on nanoparticles. The electronic properties of CO on nanoparticles are studied by the analysis of density of state and charge density. The characteristic of CO on W(n) nanoparticles are also compared with that of W bulk.

The dynamics behavior of Rh nanoclusters on boron nitride sheet.

The configurations and corresponding adsorption energies of Rh(n) (n = 4-13) nanoclusters on the boron nitride sheet are investigated by density functional theory (DFT). We use the force-matching method (FMM) to modify parameters of Morse and Tersoff potential functions. To elucidate the dynamical behaviors of Rh nanoclusters on the boron nitride sheet, molecular dynamics (MD) is applied with modified Morse potential function parameter. Finally, the square displacement (SD) is utilized the dynamics behavior of different size Rh nanoclusters at different temperatures.

A density functional theory study on the structure stability of silica nanoclusters.

The studies of silica nanoclusters are of substantial interest for large potential in applications as diverse as photonics/optics, microelectronics and catalysis. In this study, we used the basing-hopping method with Buckingham potential to get the stable structures of silica nanoclusters ((SiO2)(n) = 1-13). The global minimum geometry of silica nanoclusters were determined by density functional theory calculation. We investigated the energy gap, binding energy and second order energy difference of nanoclusters to determine their structural stability with different sizes. We also calculate the second-order energy difference, binding energy to determine the magic number.