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Reversing the thermal induced sintering phenomenon and forming high temperature stable fine dispersed metallic centers with unique structural and electronic properties is one of the ever-lasting targets of heterogeneous catalysis. Here we report that the dispersion of metallic Ni particles into under-coordinated two-dimensional Ni clusters over γ-Mo2N is a thermodynamically favorable process based on the AIMD simulation. A Ni-4nm/γ-Mo2N model catalyst is synthesized and used to further study the reverse sintering effect by the combination of multiple in-situ characterization methods, including in-situ quick XANES and EXAFS, ambient pressure XPS and environmental SE/STEM etc. The under-coordinated two-dimensional layered Ni clusters on molybdenum nitride support generated from the Ni-4nm/γ-Mo2N has been demonstrated to be a thermally stable catalyst in 50 h stability test in CO2 hydrogenation, and exhibits a remarkable catalytic selectivity reverse compared with traditional Ni particles-based catalyst, leading to a chemo-specific CO2 hydrogenation to CO., Reversing the thermal induced sintering phenomenon and forming high temperature stable fine dispersed metallic centers is one of the ever-lasting targets in heterogeneous catalysis. Here the authors report the dispersion of metallic Ni particles into under-coordinated two-dimensional Ni clusters over γ-Mo2N.

In catalysis science, the electronic structure of the active site determines the structure-activity relationship of the catalyst to a large extent. Therefore, modulating the electronic structure has become a main route for the rational design of metal-based catalyst materials. In this work, we prepared a LaCoSiHx material that has more electronegativity and a lower workfunction than traditional supported Co-based catalysts. Using CO2 methanation as a model catalytic reaction, the facile dissociation of CO2 and CO (a key reaction intermediate) on the surface of the LaCoSiHx catalyst is observed by various experimental methods (e.g., in situ Raman and FTIR) at room temperature. Moreover, theoretical calculation results further show that LaCoSiHx has a much stronger capacity for carbon-oxygen bond activation than the Co surface. The intrinsic mechanism is attributed to the marked electron transfer from catalysts into the antibonding orbital of CO2 and CO.

Cobalt carbides nanoparticles have great potential as novel materials in magnetic fields. However, it is difficult to synthesize single phase cobalt carbides, especially Co3C. In this paper, we propose a one‐pot wet‐chemistry approach to synthesize single phase ferromagnetic Co3C without using any alkali as nucleation solvent. The particle size of Co3C nanoparticle is about 3 nm. The magnetic properties of Co3C nanoparticles are measured at 300 K from –30 to 30 kOe. Compared with Co2C, Co3C exhibits a large saturation magnetization of 46.1 emu g–1 and a high coercivity of 1.5 kOe. Small amount of carbon and small particle size of the Co3C nanoparticle are believed to contribute to large magnetization and high coercivity. Magnetic measurements also reveal the spin glass behavior caused by the small Co3C nanoparticle at the spin freezing temperature of 43 K. This work provides a facile method to synthesize single phase Co3C nanoparticle which is applicable in magnetic field.

Supramolecular interaction is a kind of intermolecular interaction with molecular recognition ability. Based on molecular recognition, the design, synthesis, and assembly of novel supramolecular fu...

The carbon deposition and permeation on nickel surfaces were investigated from thermodynamic and kinetic aspects by using density functional theory (DFT), ab initio atomic thermodynamics, and class...

The pressure-induced phase transition mechanisms of gold nanoribbons (Au-NRBs) from 4H phase to FCC phase with different surface ligands were studied theoretically. In bulk form, the 4H (hexagonal)...

The mechanisms of iridium-catalyzed nonoxidative conversion of light hydrocarbons have been computed on flat Ir(111) and stepped Ir(211) surfaces under given conditions. On Ir(111), CH4 dissociatio...

Metal nanoparticles (NPs) have been commonly introduced onto flexible platforms for improving their exploitation. However, such an introducing process of NPs is hard to achieve, and additional disp...

At present, the catalytic conversion of carbon-containing resources remains a major challenge faced during the economic growth and energy mix adjustment around the world. The development of catalys...

We explored the mechanism of ethylene combustion by combining a density functional tight-binding based nanoreactor molecular dynamic method (DFTB-NMD) and a hidden Markov model (HMM) based reaction network generator approach. The results demonstrate that the DFTB-NMD is a promising method to predict the mechanism of complicated combustion reactions.

To understand the metal–support interaction of oxide supported transition metal catalysts, we computed the reaction mechanisms of dry and steam reforming of methane on a tetragonal ZrO2(101) supported Ni catalyst. Based on the limited number of active sites on the surface, an irregular and non-ideal Ni13 cluster on ZrO2(101) is identified as a catalyst. A simple reaction mechanism is proposed, and the first direct dissociation step of CO2, CH4 and H2O is the most difficult based on the computed Gibbs free energies and no surface CHXO and CHXOH intermediates are involved, different from that on the flat Ni(111) surface. Analysis of other supported nickel catalysts shows that not only the support but also the size and shape of the metal clusters play an important role in the reaction mechanisms and kinetics.

Cobalt is an important catalyst for the Fischer–Tropsch synthesis (FTS) reaction. We present a pretreatment process to enhance the activity of cobalt catalyst by carburizing it with an intermediate time. Cobalt catalyst carburized for 0.5 h showed higher activity than the cobalt catalyst without carburization and cobalt catalyst carburized for 2 h. TEM analysis revealed the existence of different phases of Co3C, Co, and Co2C for these catalysts, with Co3C showing high activity for the FTS reaction. With the help of DFT calculations, we assessed the structure–performance relationships among the Co3C, Co, and Co2C, and found that Co3C was more active for CO activation. Our study provides a new idea to rationally design Co-based FTS catalysts with high activity.

Periodic density functional theory calculations were employed to study the mechanisms of H2O dissociative adsorption on the Ni(211) surface at different coverages. Due to stronger H-bonding, H2O cl...

In order to understand the effect of in-situ carbon deposition and permeation process on cobalt-catalyzed heterogeneous reactions, the thermodynamics and kinetics of the carburization process of te...

Using our proposed structure prediction algorithm coupled with first-principles calculations, we performed crystal structure prediction on a series of iron-rich iron carbide phases (FexCy, 1 ≤ y ≤ ...

Appropriate electronic structure is vital to promote the catalytic performance of active species. In this work, TiO2–x was employed to regulate active Fe species to the electron-rich state, causing...

Deep insights into the chemical nature of surface free energy are important to achieve a rational design of solid materials with desired morphologies and functionalities such as electronic properti...

Hierarchically mesoporous iron oxide/graphene oxide (GO) composites have been synthesized by a facile, one-step hydrothermal method and utilized as Fischer–Tropsch synthesis (FTS) catalysts. The ca...

The in situ formation and removal of coke is a critical problem in heterogeneous catalysis, but its mechanism is not well understood. This work investigates the mechanism of carbon deposition and hydrogenation on an Fe cluster under high-temperature conditions with the density functional tight-binding (DFTB) based nanoreactor molecular dynamics (NMD) method. Our study shows that successive formation of carbon chains, rings, and fused rings occurred during the carbon deposition on Fe clusters. Hydrogenation of activated carbon happens through direct C-H coupling, while the hydrogenation of graphitic carbon involves hydrogenation of the edge carbon, ring-opening reaction, and dealkylation reaction. The main function of the Fe catalyst is to provide the active sites for H2 dissociation and dissociated H spillover, while its activity toward C-C bond breaking is limited. These results highlight the role of the DFTB-NMD method as an effective tool to investigate reaction mechanisms under operating conditions in heterogeneous catalysis.

Ultrasound-assisted dispersive liquid-liquid microextraction (UA-DLLME) was combined with thermospray flame furnace atomic absorption spectrometry (TS-FF-AAS) for the first time to develop a highly...

A new method for the determination of bismuth was established by combining ultrasound-assisted dispersive micro solid phase extraction (UA-DMSPE) with thermospray flame furnace atomic absorption spectrometry (TS-FF-AAS) for the first time in this work. Nanometer-sized titanium dioxide (nano-TiO2) was used as the adsorbent, and the unpacked extraction pattern simplified the operation procedure. The extraction process was assisted by ultrasound. With the application of slurry sampling, the on-line method combining UA-DMSPE with TS-FF-AAS was developed. Problems of nebulization associated with previous methods based on the coupling of FAAS and solid phase microextraction (SPME) were overcome. The combination significantly improved the analytical performance of the modified FAAS instrument. Under the optimal conditions, the limit of detection (LOD) was 0.34 μg L−1, with a sensitivity enhancement factor (EF) of 67. Compared with direct FAAS, the EF was as high as 736. The method was applied to analyze environmental water and geological samples with good agreement with certified values of the standard materials or with values obtained using ICP-MS, which demonstrated its reliability for the determination of traces of Bi in environmental samples. The proposed method provides a promising, simple and low-cost approach to develop a sensitive detection method for Bi based on FAAS.

Core–shell MFI@TON composites were designed and synthesized as a highly shape-selective catalyst for toluene alkylation with methanol by passivating the nonselective acid sites and tuning the diffusion behavior. The synthesis parameters were comprehensively investigated, indicating the importance of the Si/Al ratio compatibility of the ZSM-5 and ZSM-22 components on the formation of a core–shell structure. The synthesis process was systemically traced, which allowed the formulation of a crystallization mechanism involving the oriented crystal growth and selective fusion steps during the secondary crystallization. As a result, the MFI zeolites as the core were fully covered by the TON zeolites as the shell, yielding spherical morphology. When applied to toluene alkylation with methanol, the core–shell MFI@TON composite exhibited significantly improved para-xylene selectivity in comparison with the original, unattached, and physically mixed catalysts. The enhanced catalytic behaviors of the core–shell MFI@TON composite could be ascribed to the effective suppression of para-xylene isomerization as a result of the passivated acid sites on the external surface and the improved diffusion time and distance for the intermediates inside the channels due to the unique structure. The synthesis method for the MFI@TON composite described herein may provide a generic platform for the design of core–shell zeolites with potentially broader applicability to other porous materials with advanced applications.

Experimentally observed magnetic properties are usually statistically averaged from bulk materials and information associated with the local chemical environment cannot be specified. Against this backdrop, we propose a theoretical strategy to provide an in-depth understanding of the multi-role for metrics that may contribute to the apparent magnetic moment of iron borides. In particular, we demonstrate this strategy through systematic manipulation of the iron/boron stoichiometry of six prototype iron borides to tune their associated local structural and electronic environment to further modulate the resultant magnetic moment. The local coordinative structures of the six iron borides were resolved utilizing bond valence analysis by taking the different coordination shells into account. Furthermore, the local electronic properties of each Fe atom in these iron borides, such as charge transfer, electronic distribution, bonding feature and orbital energy level, were carefully analyzed by Bader analysis, density of states analysis and Crystal Orbital Hamilton Population analysis. From the combination of analyses of both the coordinative and electronic properties of the prototype iron borides, a linear relationship between the local magnetic moment and the bond valence as well as the average energy of the Fe 3d orbitals has been confirmed.

Spin polarized density functional theory computations were performed to elucidate electronic effects based on first-row transition metal doped Fe(100) and Fe5C2(100) surfaces for CO dissociation. Both Mn and Cr doped Fe(100) and Fe5C2(100) surfaces can enhance the dissociation of CO, while the Co, Ni and Cu doped ones are unfavorable for the dissociation of CO. Besides the BEP relationship, a linear relationship between activation energy and the electronegativity of the dopant atom is established. It can be deduced that the metals with lower electronegativity are favorable for the activation of CO. The reason has been analyzed by density of states and crystal orbital Hamilton population. The metals with lower electronegativity relative to Fe could donate electrons to doped sites and then activate CO with a more delocalized O 2p orbital. The electronic effects revealed herein are helpful for the understanding of the CO activation process and for the design of catalysts with desired activity.

Because of the structural complexity and inhomogeneity, the effect of the coordination environment on the catalytic properties is underexplored in heterogeneous catalytic systems. To address this c...

A single longitudinal mode (SLM) fiber laser with a ring cavity based on Sagnac interferometer (SI) for temperature sensing in the 2-μm band is proposed and demonstrated. The simulation and experimental results show that the transmission spectrum of the SI filter is sensitive to temperature change. Based on this distinguishing feature, the correlation between the laser wavelength drift and temperature variation can be established. Experimental results show that the proposed laser operates stably at the resonant wavelength of 1988.21 nm and the optical signal-to-noise ratio is approximately 55 dB at ambient temperature. Through continuous measurement for 100 min, the fluctuation of the output laser power is lower than 0.74 dB, and the resonant wavelength shift is less than the minimum resolution of the spectrometer of 0.05 nm. This indicates that it has good stability for a certain period of time. At the same time, the laser operates stably in SLM state. A temperature sensitivity of 2.09 nm/°C is obtained in experiment. Notably, the proposed fiber laser sensor possesses the merits including high sensitivity, low cost and simple structure, which are beneficial to its practical application.

The design of cheap, non-toxic, and earth-abundant transition metal catalysts for selective hydrogenation of alkynes remains a challenge in both industry and academia. Here, we report a new atomically dispersed copper (Cu) catalyst supported on a defective nanodiamond-graphene (ND@G), which exhibits excellent catalytic performance for the selective conversion of acetylene to ethylene, i.e., with high conversion (95%), high selectivity (98%), and good stability (for more than 60 h). The unique structural feature of the Cu atoms anchored over graphene through Cu-C bonds ensures the effective activation of acetylene and easy desorption of ethylene, which is the key for the outstanding activity and selectivity of the catalyst., It is highly desired to explore cheap, non-toxic transition metals catalysts for semihydrogenation of acetylene. Here, isolated Cu atoms anchored onto a defective nanodiamond-graphene support exhibit robust catalytic performance in acetylene semihydrogenation in comparison with supported Cu clusters.

In this work, the application of organic phase chemical vapour generation (CVG)-atomic fluorescence spectrometry (AFS) was extended, firstly investigating the feasibility and analytical performance...

Effects of a novel carbon/phenolic (CF/PR) ablator filled with acidified graphitic carbon nitride (ag-C3N4) on ablative resistance were evaluated. Ablative properties of CF/PR composites were significantly enhanced by 69.23% with incorporating 0.2 wt% ag-C3N4, ascribing to the formation of the dense carbon layer over the fibers, increased graphitization degree and more pyrolysis gases. Molecular dynamics simulations of ag-C3N4 inside the matrix confirm the origins of improved ablation resistance arising from the fact that ag-C3N4 alters the breaking patterns and spatial distribution of the polymer fragments, and reduces the graphitic growth temperature by 400 K. And the decomposition of ag-C3N4 and phenolic at the fiber-matrix interface collides the fibers' surfaces to undermine the structural integrity, which induces the phase transformation from short-range to long-range order of the matrix carbon because of the templating effect (transverse) and the interlayer π-π stacking (longitudinal) of the fibers at extremely high temperature.

Conversion of straight-chain paraffins into aromatics is particularly attractive but extremely challenging in the oil refining industry. Constructing the Pt-supported catalysts with high aromatic selectivity is vital. Here, we report a strategy to use Fe-modified KL zeolites to improve the Pt atom utilization efficiency and anchor them inside KL zeolite channels via atomic-layer deposition technique. A combination of highly dispersed single-atom Pt and electron-rich Pt clusters is fabricated on the KL zeolite through the creation of proper nucleation sites. The resulted catalyst (PtFe-1/KL) exhibits excellent performance for the n-heptane aromatization (90.1% aromatic selectivity) with an apparent activation energy of 131 kJ/mol and much enhanced stability at a relatively lower temperature (420 °C). Experimental analysis and density functional theory calculation demonstrate that the single-atom Pt might play a key role in the initial dehydrogenation of n-heptane to 1-heptene, and the superior stable Pt clusters encapsulated inside Fe-decorated KL zeolite channels accelerate the 1-heptene dehydrocyclization to aromatics. The synergetic interaction between single-atom Pt and Pt clusters enables the PtFe-1/KL catalyst to be one of the most effective n-heptane aromatization catalysts reported to date.

Iron sulfides have emerged as a fascinating class of materials in electromagnetics and catalysis areas, which however are challenging in first-principles modeling because of the strongly-correlated interactions between Fe 3d and S 3p electrons. Here, we assess the performances of 14 density functionals on the structural, electronic, and magnetic properties of five iron sulfides. The PBE + U with Ueff = 2.0 eV has the overall best performance. After evaluating functionals and obtaining reliable properties, our final goal is from predicting to correlating in order to do high throughput screening for the systems since the complex structures and phases of iron sulfides, to put it in another way, to hunting a reliable descriptor for predicting their properties. In the work, we demonstrate that the crystal orbital Hamilton population (COHP) and Bader charge of Fe atoms presents a good correlation with the empirical bond valence. Our results open a new avenue to effectively investigate phases and properties for various structures of iron sulfides. Indeed, the correlations between COHP/Bader charge and bond valence can be extended to other systems.

The surface energies and the morphologies of three iron oxides (α-Fe2O3, Fe3O4, and FeO) are systematically investigated by Density Functional Theory (DFT) employing PBE and PBE+U methods. The surface energies are computed under various O chemical potential which is directly related to atmosphere condition. Compared with available experimental observations, PBE provides reasonable prediction on surface stability of all three oxides while the results of PBE+U are not well consistent with experiments for Fe2O3. Based on the Wulff construction and calculated surface energies, the micro-crystal morphologies of three iron oxides are predicted at various oxygen chemical potential. Subsequently, on basis of the data of surface energies, the effect of surface free energies on phase equilibrium of iron oxides nanoparticles are investigated. These results suggest that particle sizes of nanometer have a significant influence on the thermodynamic equilibrium shifting due to their large surfaces energies contributions. This principle can guide people control the phase transition of iron oxides by adjusting surface energies contributions by changing the sizes of particles.

An extremely large displacement of the indium site in In–S6 octahedra in LnOInS2 (Ln = La, Ce, and Pr) was found in synchrotron X-ray diffraction. LaOInS2 with off-center indium in In–S6 octahedra exhibited a wider optical band gap than CeOInS2 and PrOInS2 with on-center indium. Therefore, the electronic structure of LnOInS2 is governed by the indium site with an extremely large displacement. All LnOInS2 produced H2 gas under visible light irradiation in the presence of sacrificial electron donors.

The properties from both bulk phases (magnetism and thermal stability) and surface (composition, orientation, and stability) of iron silicide model compounds were evaluated by a theoretical study w...

Tin-assisted fully exposed Pt clusters are fabricated on the core–shell nanodiamond@graphene (ND@G) hybrid support (a-PtSn/ND@G). The obtained atomically dispersed Pt clusters, with an average Pt a...

Metal nanoparticle (NP), cluster and isolated metal atom (or single atom, SA) exhibit different catalytic performance in heterogeneous catalysis originating from their distinct nanostructures. To maximize atom efficiency and boost activity for catalysis, the construction of structure–performance relationship provides an effective way at the atomic level. Here, we successfully fabricate fully exposed Pt3 clusters on the defective nanodiamond@graphene (ND@G) by the assistance of atomically dispersed Sn promoters, and correlated the n-butane direct dehydrogenation (DDH) activity with the average coordination number (CN) of Pt-Pt bond in Pt NP, Pt3 cluster and Pt SA for fundamentally understanding structure (especially the sub-nano structure) effects on n-butane DDH reaction at the atomic level. The as-prepared fully exposed Pt3 cluster catalyst shows higher conversion (35.4%) and remarkable alkene selectivity (99.0%) for n-butane direct DDH reaction at 450 °C, compared to typical Pt NP and Pt SA catalysts supported on ND@G. Density functional theory calculation (DFT) reveal that the fully exposed Pt3 clusters possess favorable dehydrogenation activation barrier of n-butane and reasonable desorption barrier of butene in the DDH reaction. Direct dehydrogenation has been a thematic research area resulting from the energy shortage and petroleum gas upgrading scenario. Here, the authors fabricate fully exposed Pt3 clusters and correlate dehydrogenation activity with average coordination number of Pt-Pt bond.

Cotton is often modified to minimize its disadvantages during textile processing. However, most finishing methods suffer from difficulties in finding finishing reagents and chemical aids. Here, we report a novel strategy based on a combination of the pad-dry-cure method and the construction of surface coating to expand the scope of the finishing reagent and simplify the finishing process. Polyacrylic acid (PAA) oligomer was first grafted onto cotton fiber surfaces via esterification between the carboxyl groups of PAA and the hydroxyl groups of the cellulose molecules on the cotton fiber surface. Hexadecanol was then reacted with the residual carboxyl groups of the PAA to build a lipid layer on the cotton fiber surfaces. The enhanced adsorption capability for hydrophobic molecules was verified via three reagents: stearyl trimethyl ammoium bromide (STAB), 9,10-dihydro-9-oxaco-10-phospho-10-oxide (DOPO), and 3,5-di-tert-butyl-4-hydroxybenzoic acid hexadecyl ester (Cyasorb 2908), which they offered bacterial-, flame-, and UV-resistance to the cotton fabrics, respectively. This strategy can lead to finishing technologies suitable for scale-up in the textile industry.

Most of the existing models of structural life prediction in early carbonized environment are based on accelerated erosion after standard 28 days of cement-based materials, while cement-based materials in actual engineering are often exposed to air too early. These result in large predictions of the life expectancy of mineral-admixture cement-based materials under early CO2-erosion and affecting the safe use of structures. To this end, different types of mineral doped cement-based material test pieces are formed, and early CO2-erosion experimental tests are carried out. On the basis of the analysis of the existing model, the influence coefficient of CO2-erosion of the mineral admixture Km is introduced, the relevant function is given, and the life prediction model of the mineral admixture cement-based material under the early CO2-erosion is established and the model parameters are determined by using the particle group algorithm (PSO). It has good engineering applicability and guiding significance.

Enhancing the intrinsic activity and space time yield of Cu based heterogeneous methanol synthesis catalysts through CO2 hydrogenation is one of the major topics in CO2 conversion into value-added liquid fuels and chemicals. Here we report inverse ZrO2/Cu catalysts with a tunable Zr/Cu ratio have been prepared via an oxalate co-precipitation method, showing excellent performance for CO2 hydrogenation to methanol. Under optimal condition, the catalyst composed by 10% of ZrO2 supported over 90% of Cu exhibits the highest mass-specific methanol formation rate of 524 gMeOHkgcat−1h−1 at 220 °C, 3.3 times higher than the activity of traditional Cu/ZrO2 catalysts (159 gMeOHkgcat−1h−1). In situ XRD-PDF, XAFS and AP-XPS structural studies reveal that the inverse ZrO2/Cu catalysts are composed of islands of partially reduced 1–2 nm amorphous ZrO2 supported over metallic Cu particles. The ZrO2 islands are highly active for the CO2 activation. Meanwhile, an intermediate of formate adsorbed on the Cu at 1350 cm−1 is discovered by the in situ DRIFTS. This formate intermediate exhibits fast hydrogenation conversion to methoxy. The activation of CO2 and hydrogenation of all the surface oxygenate intermediates are significantly accelerated over the inverse ZrO2/Cu configuration, accounting for the excellent methanol formation activity observed., Enhancing the intrinsic activity and space time yield of Cu based heterogeneous methanol synthesis catalysts is one of the major topics in CO2 hydrogenation. Here the authors develop a highly active inverse catalyst composed of fine ZrO2 islands dispersed on metallic Cu nanoparticles.

CO adsorption on the perfect Ir(111) as well as the unreconstructed Ir(100) and Ir(110) surfaces at different coverages has been computed at the level of periodic density functional theory. General...

The morphology change of metallic nanoparticles induced by the interaction of gas molecules with nanoparticles is a very important surface chemistry process in heterogeneous catalysis. Here, we performed a thorough study to provide understanding of the influence of CO adsorption on theoretically established Ru nanoparticle models through an approach combining density functional theory, Wulff construction, and ab initio atomistic thermodynamics. The morphology of constructed Ru nanoparticles undergoes significant evolution upon changing CO coverage, exposed temperature, and pressure. The contribution from flat facets becomes more significant in equilibrium morphology of nanoparticles as the surface CO coverage increases. Such morphological evolution has a consequential impact on the inherited catalytic performance of Ru NPs, as they were applied into three probe catalytic reactions, CO direct dissociation, HCO formation, and CH3 hydrogenation. This study enriches the current knowledge of the ruthenium nano...

For the long-term stable operation of the entrained flow gasifier in the coal chemical industry, the flux agents are generally adopted to adjust the fusibility of coal ash. Therefore, it is necessary to understand the underlying mechanism for the impact of typical oxide flux agents on viscosity temperature properties of coal ash from structures and thermodynamics. In this work, the role of calcium oxide, sodium oxide and ferrous oxide on viscosity temperature properties is investigated by a combination of molecular dynamics simulations and thermodynamic calculations. The variations of viscosity and temperature of critical viscosity are obtained for different ternary coal ash systems by thermodynamic calculation. Ternary phase diagrams are applied to evaluate the effect of different flux agents, which are also found to cause mineral transformation from high-temperature minerals to low-temperature minerals. Oxygen bond species are employed as the indicator of the structural evolution originating from addition of different flux agents. The sodium atoms may more readily weaken the tricluster oxygen bonds than calcium or ferrous atoms according to the results. Higher content of bridging oxygen bonds in the sodium oxide ternary coal ash system can enhance the stability of the structures and induce higher viscosity. Stability coefficients are defined here and a function to describe the relationship between the viscosity and flux agent content is established. The results from the current work are expected to provide new clues to find strategies controlling the fusion behaviour of coal ash systems.

Luminescent SnO2 material was synthesized by a hydrothermal assisted sol-gel method. X-ray powder diffraction analysis indicates that the as-synthesized SnO2 is a tetragonal phase and the calculated lattice parameters a and c are 0.474 and 0.318 nm, respectively. Scanning electron microscopy shows that the prepared tetragonal SnO2 particles have regular rhombic shape and are polydisperse without any agglomeration. Ultraviolet-visible absorption spectroscopy was used to study the light-absorbing properties and bandgap of tetragonal SnO2, and the value of bandgap is obtained to be 2.894 eV. The emission spectrum detected at λex = 230 nm showed two peaks located at 375 and 415 nm, the first having the strongest luminescence intensity. The fluorescence emission spectra also show that an emission peak at 510 nm is observed when the λex is 400 nm. Photocatalytic experiments indicate that the tetragonal SnO2 exhibits a strongly enhanced photocatalytic activity than commercial nano-SnO2 in photocatalytic degradation of various dyes under visible light irradiation. The photocatalytic mechanism is discussed on the basis of X-ray photoelectron spectroscopy (XPS) data, Fourier transform infrared (FTIR) spectra, electrochemical measurements and photocatalytic experiments results.

The effects of Zn-Pt interaction and Pt dispersion over a uniform compact cylindrical shape ZSM-5 (UZSM-5) on the catalytic octane aromatization performance are investigated. The comparison between different Pt- and Zn-modified ZSM-5 catalysts demonstrates the significance of ZSM-5 morphology and, more importantly, the metal distributions on it. For the UZSM-5 support, Pt atoms prefer to occupy the sites within its inner pores, resulting in high selectivity to xylenes during the octane aromatization. The Zn deposit in inner pores and higher dispersion of Pt lead to the spillover of Pt sites to the external surface, which is critical for the activation of octane to produce reaction intermediates that are further converted to aromatics over the inner pore catalytic sites. These effects are evidenced by a diffuse reflection infrared Fourier transform spectroscopy study of CO adsorbed on the catalyst surface. In situ X-ray absorption fine structure spectra are collected to probe the coordination number and the chemical environment of Pt and Zn atoms in the catalysts during the octane aromatization reaction. Pt and Zn are well dispersed and stable during the reaction, and a partial reduction of Pt during the reaction is observed. A theoretical study using the density functional theory method predicts that the reaction and transition-state intermediates upon octane activation are better stabilized by Pt(111) of Pt external surface sites with a smaller activation barrier, indicating their significance in C-H activation. This hypothesis is further evidenced by comparing the octane aromatization performance of various modified catalysts through varying Zn loading, blocking inner pores, and covering the external catalytic sites with SiO2.

Water adsorption and dissociation on clean and oxygen pre-covered Ni(111) surfaces have been computed systematically by using density functional theory and ab initio atomistic thermodynamics. The adsorption of H, O and OH prefers 3-fold faced centered cubic hollow sites, and that of H2O prefers the top site. For (H2O)n aggregation, direct O–Ni interaction and H-bonding synergistically determine the adsorption energy, which is structure insensitive for large adsorbed clusters. At low coverage (θ ≤ 0.25 ML), OH adsorbs perpendicularly and prefers remote distribution without H-bonding, and the OH saturation coverage should be 0.625 ML on the basis of H2O dissociative adsorption. The adsorption configuration for 4O (0.25 ML) prefers a p(2 × 2) structure, in agreement with the experiment, and the O saturation coverage should be 0.25 ML based on H2O dissociative adsorption. On the 0.25 ML O pre-covered Ni(111), H2O greatly prefers molecular adsorption [4O + 4H2O(s)] over dissociative adsorption [8OH] thermodynamically, and this is in agreement with the photoelectron spectroscopy results and in disagreement with previously and recently proposed results from single crystal adsorption calorimetry of D2O adsorption. It is noted that the computed bond energy and formation enthalpy of the supposed surface hydroxyls on the basis of the molecular adsorbed state [4O + 4H2O(s)] are much closer to the experimentally estimated results than those computed on the basis of the dissociatively adsorbed state [8OH]. Furthermore, the computed H2O desorption temperature on the basis of the molecular adsorbed state [4O + 4H2O(s)] is in excellent agreement with experimental results (284 vs. 275–300 K), while that from the dissociatively adsorbed state [8OH] differs strongly (197 K). All these support H2O molecular adsorption instead of dissociative adsorption, and this needs further experimental investigations and confirmations. The vibrational frequencies of 4O, 4O + 4H2O and 8OH adsorption configurations have been computed to aid experimental studies.

Constructing and understanding the doping effect of secondary metal in transition metal carbide (TMC) catalysts is pivotal for the design of low-cost hydrogen evolution reaction (HER) electrocatalysts. In this work, we developed a wet-chemistry strategy for synthesizing Co-modified Fe5C2 nanoparticles ((Fe1−xCox)5C2 NPs) as highly active HER electrocatalysts in basic solution. The structure of (Fe1−xCox)5C2 NPs was characterized by X-ray diffraction (XRD), extended X-ray absorption fine structure spectra (EXAFS) and scanning/transmission electron microscopy (S/TEM), indicating that the isomorphous substitution of cobalt in the lattice of Fe5C2. (Fe0.75Co0.25)5C2 exhibited the best HER activity (174 mV for j = −10 mA/cm2). Computational calculation results indicate that Co provides the most active site for HER. X-ray adsorption spectra (XAS) studies further suggested that the electron transfer in Fe-C bonds are enhanced by the substitution of Co, which modulates the hydrogen adsorption on the adjacent electronic-enriched carbon, and therefore promotes HER activity. Our results affirm the design of low-cost bimetallic TMCs based HER catalysts.

The effectiveness of graphene oxide (GO) on improving the ablation resistance of composite is investigated by incorporating a low concentration of GO (0.1 wt%) into the carbon/phenolic (CF/PR). The X-ray diffraction, Raman spectroscopy, scanning electron microscopy and transmission electron microscopy analyses reveal that the superiority of GO-filled composite over the neat in terms of thermal resistance is associated with the promoted char yield of PR and graphitization of fibers by the addition of GO. Molecular dynamics simulations identify the GO inside the matrix, even a small concentration, as a nuclei agent for the graphitized crystal growth of carbonized PR. And the GO at the fiber-matrix interface can bond to the fibers at extreme ablation temperatures, which promotes the formation of the Stone-Thrower-Wales defect (xy plane) and sp2 hybridization (z direction) at the graphene-fiber interface, and further increases the graphitization degree of fibers.