Vacancy Formation Energy Research Articles

New horizons of MBenes: highly active catalysts for the CO oxidation reaction.

The search for materials with high intrinsic carbon monoxide oxidation reaction (COOR) catalytic activity is critical for enhancing the efficiency of reducing CO contamination. COOR catalysts, however, have long relied heavily on noble metals and CeO2. Herein, in order to search for non-noble COOR catalysts that are more active than CeO2, 18 oxygen-functionalized MBenes with orthorhombic and hexagonal crystal structures, denoted as orth-M2B2O2 and hex-M2B2O2 (M = Ti, V, Cr, Zr, Nb, Mo, Hf, Ta and W), were investigated in terms of their COOR catalytic activity by high-throughput first-principles calculations. Hex-Mo2B2O2, orth-Mo2B2O2, hex-V2B2O2 and hex-Cr2B2O2 were found to be more active than CeO2 and possess structural stability below 1000 K, showing the potential to replace CeO2 as the substrates of COOR catalysts. Moreover, orth-Mo2B2O2, hex-V2B2O2 and hex-Cr2B2O2 exhibit even higher COOR catalytic activity than Pt-CeO2 and Au-CeO2, and are expected to be applied as COOR catalysts directly. Further investigations showed that the formation energy of oxygen vacancies could be used as the descriptor of COOR catalytic activity, which would help to reduce the amount of calculations significantly during the catalyst screening process. This work not only reports a series of 2D materials with high COOR catalytic activity and opens up a new application area for MBenes, but also provides a reliable strategy for highly efficient screening for COOR catalysts.

Resistive switching characteristics of HfO<sub><i>x</i></sub>-based resistance random access memory under photoelectric synergistic regulation

Cu/HfO<sub><i>x</i></sub>/Pt and Cu/HfO<sub><i>x</i></sub>-ZnO/Pt resistance random access memory (RRAM) devices are prepared by magnetron sputtering. The results show that the Cu/HfO<sub><i>x</i></sub>/Pt device has the stable bipolar resistive switching characteristics, good retention (as long as 10<sup>4</sup> s), and a switching ratio greater than 10<sup>3</sup>. The current conduction mechanism of HfO<sub><i>x</i></sub> device is ohmic conduction at low resistance, while space charge limited current (SCLC) mechanism dominates at high resistance, and the conductive filament is composed of oxygen vacancies. Owing to the low content and random distribution of oxygen defects in the HfO<sub><i>x</i></sub> film, the endurance and uniformity of the device are poor. Compared with HfO<sub><i>x</i></sub> device, HfO<sub><i>x</i></sub>-ZnO device exhibits lower operating voltage and better uniformity and stability. The main reason is that ZnO material has smaller formation energy of oxygen vacancy, which can produce more oxygen defects under electric field to participate in the resistive switching behavior of the device, thereby reducing the operating voltage and improving the uniformity of the device. In addition, owing to the existence of the interface between HfO<sub><i>x</i></sub> and ZnO film, the random distribution of oxygen defects is inhibited, that is, the random fracture and formation of conductive filament are inhibited, which is beneficial to improving the uniformity of the device. In addition, the resistive switching behaviors of Cu/HfO<sub><i>x</i></sub>/Pt and Cu/HfO<sub><i>x</i></sub>-ZnO/Pt RRAM devices under different intensities of 255 nm ultraviolet illumination are studied. For Cu/HfO<sub><i>x</i></sub>/Pt device, the light of 255 nm wavelength shows little effect on its resistive switching characteristics. For the Cu/HfO<sub><i>x</i></sub>-ZnO/Pt RRAM device, the operating voltage and stability of the device can be improved by increasing the light intensity. Although the switching ratio of the device decreases with the increase of light intensity, the device can exhibit multiple resistance states by adjusting different light intensities to achieve multi-level storage. Finally, the analysis of the <i>I</i>-<i>V</i> curves of the devices indicates that the two types of devices show similar resistive switching mechanisms under the illumination of light or no light, which can be explained by the resistive switching mechanism of oxygen vacancy conductive filament. Therefore, a physical model based on the oxygen vacancy conductive filament is established to explain the resistive switching behavior of the device in this paper.

Study of pnictides for photovoltaic applications.

For the transition into a sustainable mode of energy usage, it is important to develop photovoltaic materials that exhibit better solar-to-electricity conversion efficiencies, a direct optimal band gap, and are made of non-toxic, earth abundant elements compared to the state-of-the-art silicon photovoltaics. Here, we explore the non-redox-active pnictide chemical space, including binary A3B2, ternary AA'2B2, and quaternary AA'A''B2 compounds (A, A', A'' = Ca, Sr, or Zn; B = N or P), as candidate beyond-Si photovoltaics using density functional theory calculations. Specifically, we evaluate the ground state configurations, band gaps, and 0 K thermodynamic stability for all 20 pnictide compositions considered, besides computing the formation energy of cation vacancies, anion vacancies, and cation anti-sites in a subset of candidate compounds. Importantly, we identify SrZn2N2, SrZn2P2, and CaZn2P2 to be promising candidates, exhibiting optimal (1.1-1.5 eV) hybrid-functional-calculated band gaps, stability at 0 K, and high resistance to point defects (formation energies >1 eV), while other possible candidates include ZnCa2N2 and ZnSr2N2, which may be susceptible to N-vacancy formation. We hope that our study will contribute to the practical development of pnictide semiconductors as beyond-silicon light absorbers.

Neutron diffraction and DFT studies of oxygen defect and transport in higher-order Ruddlesden-Popper phase materials.

A series of higher-order Ruddlesden-Popper phase materials - La3PrNi3O10-δ , La2Pr2Ni3O10-δ and LaPr3Ni3O10-δ - were synthesised and investigated by neutron powder diffraction to understand the oxygen defect structure and propose possible pathways for oxygen transport in these materials. Further complimentary DFT calculations of the materials were performed to support the experimental analysis. All of the phases were hypostoichiometric and it was observed that the majority of the oxygen vacancies were confined to the perovskite layers, with a preference for equatorial oxygen sites. A particular preference for vacancies in O(1) and O(5) sites at high temperatures was observed from neutron diffraction measurements which were further complimented by DFT calculations wherein the vacancy formation energy was found to be lowest at the O(1) site. Also, a preference for a curved oxygen transport pathway around the NiO6 octahedra was observed which agrees with the published literature for Ruddlesden-Popper phase materials. Lattice parameters for all three compositions showed a linear increase with increasing temperature, but the increase was greatest in the c parameter while the b parameter showed only a slight increase when compared to the a parameter. The thermal expansion coefficient was calculated for all compositions and was found to be in the range 13.0-13.4 × 10-6 °C-1, which is compatible with the commonly used electrolyte materials for solid oxide fuel cells.

Fluorination Intensifying Oxygen Evolution Reaction for High-Temperature Steam Electrolysis

Solid oxide electrolysis cells (SOECs) have emerged as one of the most potent techniques for hydrogen production. As the restricted step for SOEC, as well as the most predominant obstacle to the scaled application, oxygen evolution reaction (OER) should be urgently accelerated by developing potent electrocatalysts. Despite inferior electrochemical activity to cobalt-based materials, perovskite ferrites exhibit great potential in the future with regard to good intrinsic stability and durability, abundant reserves, and good compatibility with other SOEC components. In this work, fluorination is introduced to the typical perovskite ferrite to further intensify the OER process. Ab initio calculations combined with physical–chemical characterizations are performed to reveal the mechanism. The doped F − leads to debilitating the strength of the metal–oxygen bond and then reduces the energy for oxygen vacancy formation and ion migration, which renders improvements to sub-processes of OER on the anode. The well-verified material, PrBaFe 2 O 5+δ F 0.1 (PBFOF), exhibited a low polarization resistance of 0.058 Ω cm −2 . Single cells based on PBFOF showed a high current density of 2.28 A cm −2 at 750 °C under 1.3 V. This work provides a clear insight into the mechanism of fluorination on perovskites and high-activity anode material for SOEC.

COMBINATION EFFECT OF TRANSITION METAL IMPURITIES ON THE OXYGEN VACANCY FORMATION ENERGETICS IN TIO2

The combination effect of substitutional impurities of group IVB-VIB transition metals on the oxygen vacancy formation energy in titania with rutile structure was studied by the projector augmented-wave method within the density functional theory. The pair interaction energy of impurity atoms was estimated depending on the interatomic distance. It was shown that the interaction in the Zr + Zr, Hf+Hf and Nb + Ta pairs leads to the energy preference of their orientation along the (100) direction at a distance of the lattice parameter a. The Mo + Mo and Nb + Mo pairs prefer to orient along the [001] direction at a distance of the lattice parameter c. If the impurity atoms are farther than the third neighbors, then their interaction can be neglected. It was found that the change in the formation energy of the oxygen vacancy due to doping with several impurities can be estimated as the sum of the energy changes due to single impurity divided by a coefficient whose value depends on the mutual arrangement of the impurity atoms.

DFT investigation of the dissolution trends of NiTi alloys with the B2 and B19' phases during the initial oxidation stage.

The selective corrosion of NiTi alloys was studied using density functional theory calculations, and the dissolution trends of the NiTi-B2 and NiTi-B19' phases in the initial oxidation stage were compared to predict their corrosion difference. The dissolution process of Ni and Ti was simulated by creating Ni or Ti vacancies on the unoxidized and oxidized NiTi alloy surfaces. The results show that the surface vacancy formation energy of Ti vacancies is higher than that of Ni vacancies, indicating that Ti is more difficult to dissolve than Ni. Furthermore, oxidation promotes and impedes the dissolution of Ni and Ti, respectively. This study improves the fundamental understanding of the corrosion mechanism of NiTi alloys.

Effect of low dissolved oxygen concentration on the defects and composition of regenerated passive film of Ti-6Al-4V alloy under continuous wear.

Tribocorrosion is one of the most common forms of failure of biomedical titanium alloys. As the passive film of titanium alloys is highly dependent on oxygen conditions, the passivation behavior and the microstructure of the passive film of Ti-6Al-4V under tribocorrosion in 1 M HCl with a low dissolved oxygen concentration (DOC) were studied by means of electron probe microanalysis (EPMA), Ar-ion etched X-ray photoelectron spectroscopy (XPS), focused ion beam (FIB) milling and high resolution transmission electron microscopy (HRTEM). The results showed that the protective ability of the regenerated passive film decreased sharply under low DOC. Al and V ions dissolved in excess, and a large number of oxygen atoms entered the matrix, leading to internal oxidation. Structural characterization indicated that Ti atoms occupied more metal lattice points in the regenerated passive film and that the high dislocation density in the deformed layer caused by wear facilitated the diffusion of Al and V. Finally, the first-principles calculation showed that Al had the minimum vacancy formation energy.

Hydrothermal aging mechanism of K/CeO2 catalyst in soot catalytic combustion based on the Ostwald ripening mechanism

The thermogravimetric analysis (TGA) experiment of CeO2 and K/CeO2 catalysts prepared with the incipient wetness impregnation method was carried out for the soot catalytic combustion at different K loadings before and after hydrothermal aging. The structure, morphology, and catalytic activity of CeO2 and K/CeO2 catalysts were thoroughly investigated with the means of N2 adsorption/desorption, XRD, XPS, and H2-TPR. The density functional theory (DFT) operation was applied to explain the mechanism of the decrease in catalytic activity of CeO2 and K/CeO2 catalysts after hydrothermal aging. TGA showed that the Tmax of the hydrothermal aging K/CeO2 catalyst was 505 °C, which was higher than CeO2 at 473 °C. After hydrothermal aging, CeO2 catalysts were less agglomerated than K/CeO2, and the ratio of Ce3+/Ce4+ decreases, but the mobile oxygen OII/OI ratio in the lattice were increased compared to CeO2 catalysts. DFT calculations showed that K doping significantly increases the surface energy and decreases the oxygen vacancy formation energy of (1 1 1), (2 0 0), (2 2 0), and (3 1 1) crystal planes, leading to enhanced catalytic combustion performance of the K/CeO2 catalyst soot based on the Mars-Van Krevelen mechanism. Furthermore, K doping decreased the adsorption energy of H2O and the energy barrier of K atoms diffusing near the surface of K/CeO2 catalyst crystals from 5.92 eV to 2.46 eV, which resulted in the loss of the active center number because of migration and coalescence (sintering) caused by crystal plane instability based on the Ostwald ripening mechanism.

Effect of Ta and Re on the fracture strength and creep strength of Ni/Ni<sub>3</sub>Al interface

The first principle method based on density functional theory and generalized gradient approximation is used to investigate the interaction of Ta and Re elements at Ni/Ni<sub>3</sub>Al interface and their influence on the interface strength. According to the calculations of the dissolution energy of these two alloying elements at 7 different positions, it can be concluded that in most of the stoichiometric ranges, Ta atoms preferentially occupy Ni sites in the <i>γ</i> phase, while Re atoms occupy preferentially Al sites in <i>γ'</i> phase. The doping positions do not change when these two atoms are co-alloyed. The calculation of Griffith fracture work of Ni/Ni<sub>3</sub>Al interface system shows that the doping of Ta atoms can improve the interface fracture strength of the phase boundary region between the <i>γ</i>/<i>γ'</i> coherent atomic layer and <i>γ</i> atomic layer. The interface is easier to fracture in the phase boundary area between <i>γ</i>/<i>γ'</i> coherent atomic layer and <i>γ'</i> atomic layer after Ta atoms have been doped. The doping of Re atoms can improve the interface fracture strength of the phase boundary region between <i>γ</i>/<i>γ'</i> coherent atomic layer and <i>γ'</i> atomic layer. The interface is easier to break in the phase boundary area between <i>γ</i>/<i>γ'</i> coherent atomic layer and <i>γ</i> atomic layer. The calculation results of the unstable stacking fault energy under the interface slip system <inline-formula><tex-math id="M1">\begin{document}$ [110](001) $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="6-20222103_M1.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="6-20222103_M1.png"/></alternatives></inline-formula> before and after Ta and Re alloying show that the doping of these two types of atoms increases the value of the unstable stacking fault energy of the interface, and the slip system<inline-formula><tex-math id="M2">\begin{document}$ [110](001)$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="6-20222103_M2.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="6-20222103_M2.png"/></alternatives></inline-formula> becomes difficult to start, which enhances the ability of the interface to block the movement of dislocations, thus enhancing the creep strength of the nickel base superalloy. When doping Re atoms, the effect is greater, and the unstable stacking fault energy of the interface increases by 11.1%, which is better for improving the creep strength of the system. By studying the influence of alloying atoms on the path of vacancy migration and the energy barrier, it is concluded that the doping of Ta and Re atoms can increase the vacancy formation energy and the potential barrier of vacancy migration at the interface. The doping of Re atoms increases the migration energy barriers on both sides of the interface, and the doping of Ta atoms increases the migration energy barriers of <i>γ</i> phase. The increase of the migration barrier hinders the emission and absorption of vacancies, thereby improving the creep capability of the alloy.

Fabrication of supported Pt/CeO2 nanocatalysts doped with different elements for CO oxidation: theoretical and experimental studies.

Supported Pt/CeO2 catalysts have been widely used in carbon monoxide (CO) oxidation; however, the high oxygen vacancy formation energy (Evac) in the process leads to the poor performance of these catalysts. Herein, we explored different element (Pr, Cu, or N) doped CeO2 supports using Ce-based metal-organic frameworks (MOFs) as precursors via calcination treatment. The obtained CeO2 supports were used to load Pt nanoparticles. These catalysts were systematically characterized by various techniques, and they showed superior catalytic activity for CO oxidation compared to undoped catalysts which could be attributed to the formation of Ce3+, and high amounts of Oads/(Oads + Olat) and Ptδ+/Pttotal. Moreover, density functional theory calculations with on-site Coulomb interaction correction (DFT+U) were performed to provide atomic-scale insights into the reaction process by the Mars-van Krevelen (M-vK) mechanism, which revealed that the element-doped catalysts could simultaneously reduce the adsorption energies of CO and lower reaction energy barriers in the *OOCO associative pathway.

Atomically Incorporating Ni into Mesoporous CeO2 Matrix via Synchronous Spray-Pyrolysis as Efficient Noble-Metal-Free Catalyst for Low-Temperature CO Oxidation

Low-temperature catalytic CO oxidation is an important chemical process in versatile applications, such as the H2 utilization for low-temperature H2 air fuel cells. Pt-group metal catalysts are efficient but highly cost-consuming. This work demonstrates an excellent and sixpenny catalyst with earth-abundant Ni and Ce, in which Ni ions are atomically incorporated into the CeO2 matrix (Ni-Ce-Ox) by synchronous spray-pyrolysis (SSP) of mixture nitrates of Ni and Ce. The Ni-Ce-Ox catalyst presents a mesoporous structure. Revealed by a model reaction of 1% CO, 1% O2, and 98% balance He at a space velocity of 13,200 mL/gcat/h, Ni-Ce-Ox catalysts display a typical volcano-shaped relationship between reactivity and Ni incorporation amount. The optimized Ni incorporation appears with a high Ni/Ce atomic ratio of 0.25, endowing the T50 (temperature corresponding to a CO conversion of 50%), which is lower-shifted by 165 °C than that of pristine CeO2 (266 °C). The density functional theory (DFT) calculations further indicate that the much-reduced oxygen vacancy formation energy at Ni-Ce single-atom sites boosted the adsorption activation of the CO molecule and therefore promoted the CO oxidation process. Besides, the2 Ni-Ce-Ox from the SSP method presents better performance than the counterparts from immersion and hydrothermal methods. This work paves a way to access efficient noble-metal-free catalysts for low-temperature CO oxidation.

Synergism between B and Nb Improves Fire Resistance in Microalloyed Steels

The long exposure of structural components to high temperatures (above 600 °C) negatively changes their mechanical properties, severely compromising the structural capacity of buildings and other structures in which safety is a primary concern. Developing new cheaper fire-resistant steels with better mechanical and thermal performances represents a challenging, cutting-edge materials science and engineering research topic. Alloying elements such as Nb and Mo are generally used to improve the strength at both room and high temperatures due to the formation of precipitates and harder microconstituents. This study shows that adding small amounts of boron in Nb-microalloyed fire-resistant steels may be crucial in maintaining mechanical properties at high temperatures. The widely used 66% yield-strength criteria for fire resistance was achieved at ≈574 °C for the B-added alloys. In contrast, for those without boron, this value reached ≈460 °C, representing a remarkable boron-induced mechanical strengthening enhancement. First-principles quantum mechanics calculations demonstrate that boron additions can lower 11.7% of the vacancy formation energy compared to pure ferrite. Furthermore, for Nb-added steels, the reduction in the vacancy formation energy may reach 33.2%, suggesting that the boron-niobium combination could act as an effective pinning-based steel-strengthening agent due to the formation of B-induced higher-density vacancy-related crystalline defects, as well as other well-known steel strengthening mechanisms reported in the literature. Adding boron and niobium may, therefore, be essential in designing better structural alloys.

Self-assembly CuO surface decorated with NiAl2O4 for high-temperature thermochemical energy storage: Excellent performance and strong interaction mechanism

High-temperature thermochemical energy storage materials with high energy density is the key technical support for the third generation concentrated solar power plants equipped with advanced energy storage system. CuO/Cu2O redox couple is one of the most promising systems due to its low cost and high energy density, but its application is limited by poor reaction performance. Herein, the self-assembly CuO surface decorated with 15 wt% NiAl2O4 is prepared with excellent redox reversibility and ultralong lifespan. Its reaction rate is increased by 4.2 times with re-oxidation degree increasing from 46 % to 99.9 %. The thermochemical energy density of storage and release reach −772.726 kJ/kg and 764.655 kJ/kg, respectively. After 1000 cycles, the degree of reduction and oxidation reaction can keep 99.9 % and 98 %. The material characterization shows that NiAl2O4 are uniformly and firmly loaded on the surface of CuO/Cu2O, which significantly increases the sintering temperature and improves the reaction performance. DFT studies further confirm that NiAl2O4 has a high binding energy with CuO/Cu2O and can increase the formation energy of copper vacancy. The study reveals the anti-sintering modification mechanism of CuO/Cu2O by introducing NiAl2O4, which provides a solution toward sintering resistance of high-temperature thermochemical energy storage materials.

Mechanism of Pt3Co nanocatalysts to improve the performance for oxygen reduction reactions: DFT study on oxygen adsorption and durability of different facets

Pt3Co nanocatalyst shows better oxygen reduction reaction (ORR) activity and durability toward Pt. In this paper, the oxygen adsorption, durability and the ORR mechanism of Pt3Co are investigated based on density functional theory (DFT) calculations by CASTEP code. The adsorption energy of O atom at each site on (100), (110), and (111) surfaces indicated that the adsorption strength of O atom on Pt3Co surface follows the order (100) > (110) > (111). In addition, the ORR mechanism is explored through the electron density difference, d-band center, and the ORR elementary reactions. The results are consistent with the tendency for adsorption energy and prove that the O hydrogenation step is the rate-determining step on Pt3Co (111). Furthermore, the calculation of surface Pt vacancy formation energy reveals that the Pt3Co (111) catalyst has the best durability. The results could guide the design of surface crystal orientation of Pt3Co nanocatalyst for ORR.

A Multifunctional "halide-Equivalent" Anion Enabling Efficient CsPb(Br/I)3 Nanocrystals Pure-Red Light-Emitting Diodes with External Quantum Efficiency Exceeding 23.

All-inorganic perovskite nanocrystals (NCs) are promising candidates for light-emitting diodes (LEDs) owing to their excellent optoelectronic properties. However, the pure-red perovskite LEDs (PeLEDs) available today made from mixed-halide CsPb(Br/I)3 NCs suffer from a compromise in their emission efficiency and spectral stability on account of severe trap-mediated nonradiative recombination loss, halide phase segregation, and self-doping effect, all of which are caused by the surface halide vacancies. Herein, we introduced a "halide-equivalent" anion of benzenesulfonate (BS- ) into CsPb(Br/I)3 NCs as multifunctional additive to simultaneously address the above challenging issues. Joint experiment-theory characterizations reveal that the BS- can not only passivate the uncoordinated Pb2+ related defects at surface of NCs, but also increase the formation energy of halide vacancies, resulting in substantially improved optical properties and phase stability of NCs. Moreover, electrons are expected to transfer from the CsPb(Br/I)3 NC to BS- because of the strong electron-withdrawing property of sulfonate group, which reduces the self-doping effect and alters the n-type behavior of CsPb(Br/I)3 NCs to near ambipolarity for balancing carrier injection in the device. Eventually, synergistic boost in device performance is achieved for pure-red PeLEDs with Commission Internationale del'Eclairage color coordinates of (0.70, 0.30) and a champion external quantum efficiency of 23.5%, which is a record value among the ever-reported red PeLEDs approaching to the Rec. 2020 red primary color. Moreover, the BS- -modified PeLEDs demonstrates robust spectral stability, showing negligible wavelength shift under different operating voltages. This strategy paves an efficient way for improving the efficiency and stability of pure-red PeLEDs. This article is protected by copyright. All rights reserved.

Toward a Consistent Prediction of Defect Chemistry in CeO2.

Polarizable shell-model potentials are widely used for atomic-scale modeling of charged defects in solids using the Mott-Littleton approach and hybrid Quantum Mechanical/Molecular Mechanical (QM/MM) embedded-cluster techniques. However, at the pure MM level of theory, the calculated defect energetics may not satisfy the requirement of quantitative predictions and are limited to only certain charged states. Here, we proposed a novel interatomic potential development scheme that unifies the predictions of all relevant charged defects in CeO2 based on the Mott-Littleton approach and QM/MM electronic-structure calculations. The predicted formation energies of oxygen vacancies accompanied by different excess electron localization patterns at the MM level of theory reach the accuracy of density functional theory (DFT) calculations using hybrid functionals. The new potential also accurately reproduces a wide range of physical properties of CeO2, showing excellent agreement with experimental and other computational studies. These findings provide opportunities for accurate large-scale modeling of the partial reduction and nonstoichiometry in CeO2, as well as a prototype for developing robust interatomic potentials for other defective crystals.

Strong electronic metal-support interactions on supported Pt catalysts for efficient perhydrogenation of polyaromatics to aviation fuels

Selective deep hydrosaturation of polyaromatics has attracted significant attention in reinforcing the utilization of heavy resources and decreasing the emission of harmful particulate matters. Herein, supported Pt catalysts on diverse oxide supports (SiO2, TiO2, CeO2) were prepared using an enhanced strong electrostatic adsorption tactics. Strong electronic metal-support interactions (EMSI) in Pt/TiO2 and Pt/CeO2 leaded to the well-dispersed electron-deficient Ptδ+ substances and intensified hydrogen spillover capacity, where the most Ptδ+ and spillover hydrogen were acquired on Pt/CeO2 ascribed to the maximal EMSI and lower oxygen vacancy formation energy heightened the adsorption of metallic Pt. Moreover, the Ptδ+ species displayed promoted H2 dissociation ability and boosted adsorption energy for aromatic. In phenanthrene hydrogenation, Pt/TiO2 presented better activity and selectivity to deep hydrosaturation products than Pt/SiO2 catalyst, indicating the enhancement of EMSI in hydrogenation. Meanwhile, the catalytic properties were further improved over Pt/CeO2 exhibiting the highest rate of 3.63 × 10−4 mol·kg−1·s−1. It delivered almost 100% conversion and selectivity to deep hydrogenation at 220 °C because of the maximal of Ptδ+ species with superb dispersion and hydrogen spillover. Furthermore, the DFT calculations manifested the enhanced adsorption of aromatic on Ptδ+ species promoting deep hydrogenation.

Development of a semi-empirical interatomic potential appropriate for the radiation defects in V-Ti-Ta-Nb high-entropy alloy

High-entropy alloys (HEAs) hold promise as candidate structural materials in future nuclear energy systems. Body-centred cubic V-Ti-Ta-Nb HEAs have received extensive attention due to their excellent mechanical properties. In this work, the Finnis-Sinclair interatomic potential for quaternary V-Ti-Ta-Nb HEAs has been fitted based on the defect properties obtained with the density functional theory (DFT) calculations. The new potential for Nb accurately reproduces the vacancy formation energy, vacancy migration energy and interstitial formation energy. The typical radiation defect properties predicted by the alloy potential were consistent with the DFT results, including the binding energies between substitutional solute atoms, the binding energy between substitutional atoms and vacancies, and the formation energy of interstitial solute atoms. In addition, the mixing enthalpies of the alloys were also consistent with the DFT results. The present potential can also describe reasonably the collision cascade process of quaternary V-Ti-Ta-Nb HEAs.

The role of crystalline phase of zirconia in catalytic conversion of ethanol to propylene

Zirconia catalysts can selectively convert ethanol to propylene and exhibit excellent catalytic stability. However, the effects of crystalline phase of ZrO2 on the catalyst active sites and catalytic performance have not been fully recognized. In this work, when Y or La was doped into ZrO2, the monoclinic to tetragonal phase transition occurred, and the propylene yields were improved to 44.0% and 42.3%, respectively. The effects of different crystalline phases of ZrO2 on the ethanol to propylene reaction were analyzed by density functional theory. Comparing the monoclinic, tetragonal and cubic phases of ZrO2, the tetragonal phase ZrO2 has the lowest oxygen vacancy formation energy and is likely to form oxygen vacancies to convert ethanol to propylene. Moreover, the adsorption energy of ethanol on tetragonal ZrO2 is moderate, which is not only beneficial to ethanol conversion, but also reduces catalyst deactivation caused by excessive adsorption. Therefore, tetragonal ZrO2 shows practical significance for catalyzing ethanol to propylene.