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NOx is frequently invoked as an oxidant for direct selective conversion of methane into methanol (DSCMM), which has long been considered one of the holy grails in green chemistry. A challenge in studying the use of NOx in oxidizing methane is the interconversion of various NOx compounds as well as the easy formation of O2, rendering it difficult to draw firm conclusions on the oxidant. Here, we explicitly elucidate the strengths of using dual oxidants (NO and N2O) for DSCMM over various phosphotungstic acid-supported single-atom catalysts. A competitive but cooperative multi-functional protocol involving dual oxidants is proposed to enhance catalytic performance due to its overall strong CH4 adsorption and thermodynamic favorability compared with normal mechanisms (single O2, N2O, or NO). The new cooperative multi-functional mechanism strategy is expected to motivate further research to elaborate on its potential advantages in DSCMM and other relevant catalytic systems.

A solvation-driven catalyst-free H2 generation system from water and various waste hydrosilanes at room temperature was developed, with good to quantitative H2 yields in minutes. Using a green solvent is found to promote the strong coordination of proton carriers with hydrosilane to liberate H2 based on molecular dynamics simulations. Theoretical calculations clarify that OH−in situ generated from H2O enabled by solvation is favorable for activating the Si–H species of hydrosilane, and the in situ formed Si–OH interacts more effectively with the adjacent remaining Si–H, both contributing to the overall enhanced H2 generation. Moreover, the overall life-cycle impacts of the developed system are less than those of industrial H2 production processes, especially in ozone layer depletion and abiotic depletion resources – fossil fuels. This protocol realizes the potential of efficiently producing H2 from waste and water, and opens a new avenue to alleviate petroleum consumption.

Chemocatalytic upgrading of the greenhouse gas CO2 to valuable chemicals and biofuels has attracted broad attention in recent years. Among the reported approaches, N-formylation of CO2 with an amine is of great significance due to its versatility in the construction of N-containing linear and cyclic skeletons. Herein, a stable N-heterocyclic carbene-carboxyl adduct (NHC-CO2) was facilely prepared and could be used as a recyclable zwitterionic catalyst for efficient CO2 reductive upgrading via either N-formylation or further coupling with cyclization under mild conditions (25 °C, 1 atm CO2) using hydrosilane as a hydrogen source. More than 30 different alkyl and aromatic amines could be transformed into the corresponding formamides or benzimidazoles with remarkable yields (74%–98%). The electronic effect of the introduced substituent on NHC-CO2 was found to evidently affect the thermostability and nucleophilicity of the zwitterionic catalyst, which is directly correlated with its catalytic activity. Moreover, NHC-CO2 could supply CO2 by in situ decarboxylation at a specific temperature that is dependent on the introduced substituent type. Experimental and computational studies showed that the carboxyl species on NHC-CO2 was not only a nucleophilic center, but also a C1 source which rapidly captures or substitutes ambient CO2 during hydrosilylation. In addition, a simple and green conceptual process was designed for the product purification and catalyst recycling, with a good feasibility for small-scale production.

In the present paper, the mechanisms of N2O reduction by H2 were systemically examined over various polyoxometalate-supported single-atom catalysts (SACs) M1/PTA (M = Fe, Co, Mn, Ru, Rh, Os, Ir, and Pt; PTA = [PW12O40]3-) by means of density functional theory calculations. Among these M1/PTA SACs, Os1/PTA SAC possesses high activity for N2O reduction by H2 with a relatively low rate-determining barrier. The favorable catalytic pathway involves the first and second N2O decomposition over the Os1/PTA SAC and hydrogenation of the key species after the second N2O decomposition. Molecular geometry and electronic structure analyses along the favorable reaction pathway indicate that a strong charge-transfer cooperative effect of metal and support effectively improves the catalytic activity of Os1/PTA SAC. The isolated Os atom not only plays the role of adsorption and activation of the N2O molecule but also works as an electron transfer medium in the whole reaction process. Meanwhile, the PTA support with very high redox stability has also been proven to be capable of transporting the electron to promote the whole reaction. We expect that our computation results can provide ideas for designing new SACs for N2O reduction by using H2 selective catalytic reduction technology.

This article outlines the various processes for CNT growth. The surface morphology of carbon nanotubes on carbon nanotubes was characterized by scanning electron microscopy (TEM) and transmission electron microscopy (TEM). Bifurcated carbon nanotubes were founded. Mechanism analysis was studied of bifurcated carbon nanotubes from chemical crystallization bifurcation and nonlinear dynamic bifurcation. At present, 5nm or 7nm chip fabrication is limited by quantum effects, which makes Moore's Law invalid. Bifurcated carbon nanotubes may be the development direction of new transistors.

In general, reduction of N2O by CO is first performed by N2O decomposition over a catalyst surface to release N2 and form an active oxygen species, and subsequently CO is oxidized by the active oxygen species to produce CO2. However, the strong adsorption behavior of CO on the catalyst surface usually inhibits adsorption and decomposition of N2O, which leads to a low activity or poisoning of catalysts. In the present paper, a Mans–van Krevelen (MvK) mechanism has been probed based on a series of phosphotungstic acid (PTA) supported single-atom catalysts (SACs), M1/PTA (M = Fe, Co, Mn, Rh, Ru, Ir, Os, Pt, and Pd). Although the calculated adsorption energy of CO is exceedingly higher than N2O for our studied systems, the adsorbed CO could react with the surface oxygen atom of the PTA support through the MvK mechanism to form an oxygen vacancy on the PTA surface. N2O acts as an oxygen donor to replenish the PTA support and release N2 in the whole reaction process. This proposed reaction mechanism avoids comp...

Recently, there are contradictory picture of the surface processes for polyoxometalates (POMs) supported single–atom catalysts (SACs) in CO oxidation, both Langmuir–Hinshelwood (LH) and Mars–van Krevelen (MvK) mechanisms have been proposed based on experimental and theoretical studies. We here present results of density functional theoretical (DFT) calculations on the neutral phosphotungstic acid (PTA) supported Rh SAC (Rh1/PTA), aiming at the identification of an Rh–assisted MvK mechanism. The main finding of our DFT calculations are: (1) two CO molecules adsorb simultaneously at the Rh site with considerable adsorption energy, which inhibits the adsorptions of O2; (2) anchoring of single Rh atom on the PTA surface weakens W–Ob/Oc bonds and leads to the charge rearrangement of the surface oxygen species; (3) the anchored Rh atom serves as an electron reservoir along the favorable pathway, as supported by the Rh atom acts as electron acceptor in formation of oxygen vacancy and electron donor in the replenishing step; (4) the difference between Ob and Oc atoms of PTA surface is remarkable, the calculated barrier for vacancy formation by reaction with adsorbed CO and Ob atom is lower than that of Oc atom (25 kcal mol–1 vs 40 kcal mol–1, however, previous experimental and theoretical studies neglect this remarkable difference of the Ob and Oc atoms in CO oxidation, which were treated indiscriminately.); (5) although the O2 molecule was activated by the charge transfer from the anchoring Rh atom to π* antibonding orbital of O2, a strong bonding interaction of Rh–O2 leads to a high barrier of 41 kcal mol–1. Therefore, the dissociation of the adsorbed O2 molecule is the rate–determining step for the whole catalytic cycle. Consequences of these findings for the Rh–assisted MvK mechanism on the Rh1/PTA SAC, can be viewed as a model system for POM–supported SACs.

Density functional theory (DFT) calculations have been employed to probe the reaction mechanism of NO reduction with CO over a Cu1/PMA (PMA is the phosphomolybdate, Cs3PMo12O40) single-atom catalyst (SAC). Several important aspects of the catalytic system were addressed, including the generation of oxygen vacancies (Ov), formation of N2O2 intermediates, scission of the N-O bond of N2O2 intermediates to form N2O or N2, and decomposition of N2O to form N2. Unlike most previous theoretical studies, which tend to explore the reaction mechanism of polyoxometalate (POM) systems based on the isolated anionic unit, here, we build a model of the catalytic system with neutral species by introduction of counter cations to model the solid structure of the Cu1/PMA SAC. The major findings of our present study are: (1) CO adsorption on Cu sites leads to the formation of cationic Cu carbonyl species; (2) the Oc atom at the surface of the PMA support can easily react with the adsorbed CO to generate a Cu-Ov pair; (3) the Cu-Ov pair embedded on PMA is found to be the active site, not only for the formation of N2O2* by the reaction of two NO molecules via an Eley-Rideal pathway but also for the decomposition of N2O to form N2; (4) the adsorption of a NO molecule on the Cu-Ov pair with a bridging model results in charge transfer from the Cu atom to the π* antibonding orbital of the NO molecule; (5) IR spectroscopy of the key intermediates has been identified based on our DFT calculations; and (6) the Cu atom serves as an electron acceptor in Ov formation steps and an electron donor in N2O2 decomposition steps, and thus represents an electron reservoir. These results suggest that the POM-supported SAC with the cheaper Cu element is an efficient catalyst for the reaction between CO and NO.

The discrete anionic structure of polyoxometalates (POMs) at the interface is more like a separate small "island", which effectively prevents the diffusion of single atoms and prohibits the agglomeration and generation of metal particles; thus, POMs can enhance the sintering-resistant behavior and increase metal loading on the surface of single-atom catalysts (SACs). To explore the catalytic performance of POM-supported SACs for CO oxidation, we employed density functional theory (DFT) calculations to gain an understanding of some important aspects, including the CO adsorption, the formation of oxygen vacancies, and the activity of the surface oxygen species, of the catalytic system. Compared to previous theoretical studies, in which the catalytic behavior of POMs has been investigated based on the anionic unit with the highest negative charge, herein, we have constructed a model of the POM-supported SACs, which are neutral species. Our DFT calculations indicated that in the series of the SACs studied herein, (1) upon anchoring of a single metal atom on the POM surface, four key surface oxygen atoms were lifted from the POM surface to form a new interface, and thus, the surface oxygen species were activated; (2) CO adsorbed more strongly on the Ir, Os, Rh, Pt, and Ru sites than on the Fe, Mn, and Co sites; (3) it was easy to form an oxygen vacancy on the POM surface in the case of the Pt system when compared with the other systems; (4) the difference in the surface oxygen species for CO oxidation was remarkable, and the Oc atom at the catalyst interface had higher reactivity for CO oxidation as compared to the Ob atom in the Pt system studied herein; and (5) the single Pt atom served as an electron reservoir in the CO oxidation along the reaction pathway.

Biodiesel, a kind of promising alternative renewable energy, is of great significance in replacing conventional fossil energy resources. Herein, for purpose of improving the preparation technology of biodiesel through efficient and convenient modifying the well-dispersion of active sites of magnetic catalysts, Fe3O4@SiO2-SO3H (P) and Fe3O4@SiO2-SO3H (S) catalysts synthesized respectively via co-precipitation and solvothermal preparation methods, were successfully employed for biodiesel production. Fe3O4@SiO2-SO3H (S) bearing the uniform core-shell nanometer microsphere structure and good dispersibility that was beneficial to the substrates touch with efficient acidic sites along with acid density of 1.8 mmol g−1, was demonstrated to furnish biodiesel in a higher yield of 97.8 %, which was better than that of Fe3O4@SiO2-SO3H (P) (88.2 % yield) at 65 °C within 4 h. The kinetic study revealed that Fe3O4@SiO2-SO3H (S)-catalyzed esterification fitted the first order model along with a low activation energy (47.9 kJ/mol), further clarifying the reason for the good catalytic performance of Fe3O4@SiO2-SO3H (S). More importantly, thermal filtration and reusability experiments confirmed the catalyst heterogeneous catalytic behavior and good reusability. The involved reaction mechanism was also interpreted, in which the Fe3O4@SiO2-SO3H (S) acid catalyst was determined to be favorable for accelerating oleic acid conversion to biodiesel via density functional theory (DFT) calculations. Finally, given economic and environmental perspective, by analyzing the potential of the industrial application of Fe3O4@SiO2-SO3H (S) and comparing its catalytic performance with other reported catalysts, its promising value in terms of transforming fatty acids and non-food oils into biodiesel could be anticipated.

In the present paper, the mechanisms of N

Molecular geometry, electronic structure, and possible reaction mechanism of a series of mono-transition-metal-substituted Keggin-type polyoxometalate (POM)–dinitrogen complexes [PW11O39M(N2)]n− (M...

The discrete anionic structure of polyoxometalates (POMs) at the interface is more like a separate small "island", which effectively prevents the diffusion of single atoms and prohibits the agglomeration and generation of metal particles; thus, POMs can enhance the sintering-resistant behavior and increase metal loading on the surface of single-atom catalysts (SACs). To explore the catalytic performance of POM-supported SACs for CO oxidation, we employed density functional theory (DFT) calculations to gain an understanding of some important aspects, including the CO adsorption, the formation of oxygen vacancies, and the activity of the surface oxygen species, of the catalytic system. Compared to previous theoretical studies, in which the catalytic behavior of POMs has been investigated based on the anionic unit with the highest negative charge, herein, we have constructed a model of the POM-supported SACs, which are neutral species. Our DFT calculations indicated that in the series of the SACs studied herein, (1) upon anchoring of a single metal atom on the POM surface, four key surface oxygen atoms were lifted from the POM surface to form a new interface, and thus, the surface oxygen species were activated; (2) CO adsorbed more strongly on the Ir, Os, Rh, Pt, and Ru sites than on the Fe, Mn, and Co sites; (3) it was easy to form an oxygen vacancy on the POM surface in the case of the Pt system when compared with the other systems; (4) the difference in the surface oxygen species for CO oxidation was remarkable, and the Oc atom at the catalyst interface had higher reactivity for CO oxidation as compared to the Ob atom in the Pt system studied herein; and (5) the single Pt atom served as an electron reservoir in the CO oxidation along the reaction pathway.

In general, reduction of N

The block copolymer solutions were prepared by dissolving polyethylene glycol/polybutylene terephthalate (PEG-b-PBT) with different intrinsic viscosities in chloroform. The composite ultrafine nanofibers of PEG-b-PBT and PEG-b-PBT-HA(hydroxyapatite) were obtained by gas-electrospun, and were characterized by scanning electron microscopy (SEM), horizontal attenuated total reflectance for Fourier transform infrared spectrometer (HATR-FTIR), dynamic contact angle measuring apparatus and differential scanning calorimetry (DSC). The gas-electrospun fibrous membranes, which were made of ultrafine fibers with average diameter 180-1200nm and well-interconnected pores, were possessed with high surface-to-volume ratio and excellent hydrophilicity. The above results strongly suggest that fibrous membranes combine advantages of synthetic biodegradable polymers and nanometer-scale dimension for mimicking the natural ECM, and may represent an ideal tissue engineering scaffold, particularly for soft tissue, such as skin and cartilage tissue engineering scaffold.

To investigate the prognostic factors for patients with thoracic ossification of the ligamentum flavum (OLF) and thoracic ossification of posterior longitudinal ligament (OPLL).Clinical information of 83 patients suffering from thoracic OLF and OPLL was reviewed retrospectively from January 2006 to June 2010. The related factors such as gender, age, preoperative and postoperative Japanese Orthopedic Association (JOA) score, pathological segment, type of thoracic OPLL, degree of thoracic kyphosis, anteroposterior diameter of OPLL, range of circumferential decompression, cerebrospinal fluid leakage or not and dysfunction or not and carotid lumbar disorders or not were analyzed by Chi-square and Logistic regression.All cases were classified into desirable group (58 cases) and undesirable group (25 cases) based on the postoperative JOA score improvement rate. Comparison of physical characteristics between two groups of age, preoperative JOA and the course of the disease had not statistically significant (P0.05). Two groups in pathological segment of thoracic OPLL (χ(2) = 6.290, P = 0.043), the ossification type of OPLL (χ(2) = 5.361, P = 0.021) and dysfunction or not in preoperative (χ(2) = 27.711, P = 0.000) had significant difference. Logistic regression analysis showed that the upper thoracic segments (P = 0.044), beak type ossification (P = 0.023) and with dysfunction in preoperative (P = 0.009) were risk factors. There were 24 patients (28.9%) with cerebrospinal fluid leakage, 3 patients with early postoperative deep infection and neurological deterioration of 2 cases in postoperative.Patients with ossification on the upper section of thoracic have a better prognosis, but the beaked localized longitudinal ligament ossification in patients and associated with preoperative dysfunction show a poor prognosis, combined jumping segmental ossification and cervical or lumbar severe disorders are the influencing factor for poor prognosis.