Efficient conversion of syngas to linear α-olefins by phase-pure χ-Fe5C2.

Oil has long been the dominant feedstock for producing fuels and chemicals, but coal, natural gas and biomass are increasingly explored alternatives1-3. Their conversion first generates syngas, a mixture of CO and H2, which is then processed further using Fischer-Tropsch (FT) chemistry. However, although commercial FT technology for fuel production is established, using it to access valuable chemicals remains challenging. A case in point is linear α-olefins (LAOs), which are important chemical intermediates obtained by ethylene oligomerization at present4-8. The commercial high-temperature FT process and the FT-to-olefin process under development at present both convert syngas directly to LAOs, but also generate much CO2 waste that leads to a low carbon utilization efficiency9-14. The efficiency is further compromised by substantially fewer of the converted carbon atoms ending up as valuable C5-C10 LAOs than are found in the C2-C4 olefins that dominate the product mixtures9-14. Here we show that the use of the original phase-pure χ-iron carbide can minimize these syngas conversion problems: tailored and optimized for the process of FT to LAOs, this catalyst exhibits an activity at 290 °C that is 1-2 orders higher than dedicated FT-to-olefin catalysts can achieve above 320 °C (refs. 12-15), is stable for 200 h, and produces desired C2-C10 LAOs and unwanted CO2 with carbon-based selectivities of 51% and 9% under industrially relevant conditions. This higher catalytic performance, persisting over a wide temperature range (250-320 °C), demonstrates the potential of the system for developing a practically relevant technology.

Systematic investigation on the rational design and optimization of bi-based metal oxide semiconductors in photocatalytic applications.

To address the global energy shortage and mitigate greenhouse gas emissions on a massive scale, it is critical to explore novel and efficient photocatalysts for the utilization of renewable resources. Bi-based metal oxide (BixMOy) semiconductors composed of bismuth, transition metal, and oxygen atoms have demonstrated improved photocatalytic activity and product selectivity. The vast number of element combinations available for BixMOymaterials provides a huge compositional space for the rational design and isolation of promising photocatalysts for specific applications. In this study, we have systematically investigated the electronic and optical properties over Bi2O3and a series of selected BixMOygroup materials (BiVO4, BiFeO3, BiCoO3, and BiCrO3) by calculating band structure, basic optical property features, mobility and separation of charge carriers. It is clearly noted that the band gap and band edge position of the BixMOygroup materials can be tuned in a wide range in comparison to Bi2O3. Similarly, the light response of BixMOyalso can be broadened from the ultraviolet to the visible light region by adjusting the selection of transition metals. Additionally, the analysis of the effective mass of charge carriers of these materials further confirms their possibility in photocatalytic reaction applications because of the appropriate separation efficiency and mobility of carriers. A selection of experimental investigations on the crystal structure, composition, and optical properties of Bi2O3, BiVO4, and BiFeO3as well as their catalytic performance in the degradation of methylene blue over was also conducted, which agree well with the theoretical predictions.

Nanoscale Valley Modulation by Surface Plasmon Interference.

Excitons in two-dimensional (2D) materials have attracted the attention of the community to develop improved photoelectronic devices. Previous reports are based on direct excitation where the out-of-plane illumination projects a uniform single-mode light spot. However, because of the optical diffraction limit, the minimal spot size is a few micrometers, inhibiting the precise manipulation and control of excitons at the nanoscale level. Herein, we introduced the in-plane coherent surface plasmonic interference (SPI) field to excite and modulate excitons remotely. Compared to the out-of-plane light, a uniform in-plane SPI suggests a more compact spatial volume and an abundance of mode selections for a single or an array of device modulation. Our results not only build up a fundamental platform for operating and encoding the exciton states at the nanoscale level but also provide a new avenue toward all-optical integrated valleytronic chips for future quantum computation and information applications.

All-polymer monolithic resonant integrated optical gyroscope.

Resonant integrated optical gyroscopes (RIOGs) can integrate discrete optical components as a promising candidate for high-performance micro-optical gyroscopes. However, the current RIOG still consists of discrete elements due to the difficulty and complexity of heterogeneous integration of resonator and modulators. This paper presents on-chip integration of optical functional components including modulator, resonator, beam splitter, and coupler for the organic-polymer-based RIOG. Simple integrated optical processes such as spin coating, lithography, and etching can realize RIOG chips with low cost, size, weight, and power (CSWaP) features. Thereinto, the electro-optic modulator (EOM) fabricated by self-synthesized electro-optic (EO) polymer (side chain bonded polyurethane imide) exhibits less than 2 V half-wave voltage, which is half of the lithium niobate (LiNbO3) modulator. With respect to the resonator, a quality factor of approximately million was achieved using low-loss fluorinated polymer. In addition, the angular velocity sensing of RIOG was also investigated. By demonstrating the monolithic integration of the resonator and modulators, such an all-polymer RIOG chip prototype builds the technical foundation for the precision fully integrated optical gyroscope.

Selective and Stable Non-Noble-Metal Intermetallic Compound Catalyst for the Direct Dehydrogenation of Propane to Propylene.

A non-noble intermetallic compound catalyst consisting of Ni3Ga nanoparticles supported on Al2O3 that exhibits high selectivity (∼94%), comparable activity (TOF = 4.7 × 10-2 s-1), good stability (∼94% to 81% over the 82 h test), and regenerability in the direct dehydrogenation of propane to propylene at 600 °C has been developed. Through synthesis techniques that stabilize the Ni3Ga phase, the surface composition of the catalytic nanoparticles could be tuned by Ni and Ga loading such that improved selectivity toward propylene may be achieved. Comparisons with well-defined silica-supported Ni3Ga and NiGa catalysts and Ni3Ga/Al2O3 with a range of Ni:Ga loading suggested that a specific surface composition range was most promising for propylene production. The presence of Ni at the active particle surface was also found to be critical to drive dehydrogenation and enhance conversion, whereas the presence of Ga was necessary to attenuate the reactivity of the surface to improve selectivity and catalyst stability.

Fabrication of light, flexible and multifunctional graphene nanoribbon fibers via a 3D solution printing method.

Graphene oxide nanoribbons (GONRs) are one of the most promising carbon based materials. The integration of 2D GONR sheets into macroscopic materials, such as continuous fibers or film, leads the way in translating the good properties of individual GONR sheets into macroscopic and ordered materials for future applications. In this study, we first report the fabrication of GONR fibers utilizing GONR sheets as the raw material without any supporting surfactant or polymer. The method of fabricating fibers is referred to as '3D solution printing'. GONR fibers exhibit good mechanical and electrical properties, whose tensile strength and electrical conductivity could reach up to 95 MPa and 680 S cm-1, respectively. Hence, the fabricated 3D integrated circuits are lighter and smaller compared to traditional metal circuits, and with high electrical properties. The 3D integrated circuits, therefore, have a bright future prospect.

Synthesis of silver nanostructures by multistep methods.

The shape of plasmonic nanostructures such as silver and gold is vital to their physical and chemical properties and potential applications. Recently, preparation of complex nanostructures with rich function by chemical multistep methods is the hotspot of research. In this review we introduce three typical multistep methods to prepare silver nanostructures with well-controlled shapes, including the double reductant method, etching technique and construction of core-shell nanostructures. The growth mechanism of double the reductant method is that different favorable facets of silver nanocrystals are produced in different reductants, which can be used to prepare complex nanostructures such as nanoflags with ultranarrow resonant band bandwidth or some silver nanostructures which are difficult to prepare using other methods. The etching technique can selectively remove nanoparticles to achieve the aim of shape control and is widely used for the synthesis of nanoflowers and hollow nanostructures. Construction of core-shell nanostructures is another tool to control shape and size. The three methods can not only prepare various silver nanostructures with well-controlled shapes, which exhibit unique optical properties, such as strong surface-enhanced Raman scattering (SERS) signal and localized surface plasmon resonance (LSPR) effect, but also have potential application in many areas.

Development of supported intermetallic compounds: advancing the Frontiers of heterogeneous catalysis.

Intermetallic compound (IMC) catalysts have garnered significant attention due to their unique surface and electronic properties, which can lead to enhanced catalytic performance compared to traditional monometallic catalysts. However, developing IMC materials as high-performance catalysts has been hindered by the inherent complexity of synthesizing nanoparticles with well-defined bulk and surface compositions. Achieving precise control over the composition of supported bimetallic IMC catalysts, especially those with high surface area and stability, has proven challenging. This review provides a comprehensive overview of the recent progress in developing supported IMC catalysts. We first examine the various synthetic approaches that have been explored to prepare supported IMC nanoparticles with phase-pure bulk structures and tailored surface compositions. Key factors influencing the formation kinetics and compositional control of these materials are discussed in detail. Then the strategies for manipulating the surface composition of supported IMCs are delved into. Applications of high-performance supported IMCs in important reactions such as selective hydrogenation, reforming, dehydrogenation, and deoxygenation are comprehensively reviewed, showcasing the unique advantages offered by these materials. Finally, the prevailing research challenges associated with supported IMCs are identified, including the need for a better understanding of the composition-property relationships and the development of scalable synthesis methods. The prospects for the practical implementation of these versatile catalysts in industrial processes are also highlighted, underscoring the importance of continued research in this field.

Three-dimensional hidden phase probed by in-plane magnetotransport in kagome metal CsV3Sb5 thin flakes.

Transition metal compounds with kagome structure have been found to exhibit a variety of exotic structural, electronic, and magnetic orders. These orders are competing with energies very close to each other, resulting in complex phase transitions. Some of the phases are easily observable, such as the charge density wave (CDW) and the superconducting phase, while others are more challenging to identify and characterize. Here we present magneto-transport evidence of a new phase below ~ 35 K in the kagome topological metal CsV3Sb5 (CVS) thin flakes between the CDW and the superconducting transition temperatures. This phase is characterized by six-fold rotational symmetry in the in-plane magnetoresistance (MR) and is connected to the orbital current order in CVS. Furthermore, the phase is characterized by a large in-plane negative magnetoresistance, which suggests the existence of a three-dimensional, magnetic field-tunable orbital current ordered phase. Our results highlight the potential of magneto-transport to reveal the interactions between exotic quantum states of matter and to uncover the symmetry of such hidden phases.

Nematic Ising superconductivity with hidden magnetism in few-layer 6R-TaS2.

In van der Waals heterostructures (vdWHs), the manipulation of interlayer stacking/coupling allows for the construction of customizable quantum systems exhibiting exotic physics. An illustrative example is the diverse range of states of matter achieved through varying the proximity coupling between two-dimensional (2D) quantum spin liquid (QSL) and superconductors within the TaS2 family. This study presents a demonstration of the intertwined physics of spontaneous rotational symmetry breaking, hidden magnetism, and Ising superconductivity (SC) in the three-fold rotationally symmetric, non-magnetic natural vdWHs 6R-TaS2. A distinctive phase emerges in 6R-TaS2 below a characteristic temperature (T*) of approximately 30 K, which is characterized by a remarkable set of features, including a giant extrinsic anomalous Hall effect (AHE), Kondo screening, magnetic field-tunable thermal hysteresis, and nematic magneto-resistance. At lower temperatures, a coexistence of nematicity and Kondo screening with Ising superconductivity is observed, providing compelling evidence of hidden magnetism within a superconductor. This research not only sheds light on unexpected emergent physics resulting from the coupling of itinerant electrons and localized/correlated electrons in natural vdWHs but also emphasizes the potential for tailoring exotic quantum states through the manipulation of interlayer interactions.

Microstructure and physical properties of two charge density wave states in NbSe3 nanowires.

The whisker-like niobium triselenide (NbSe3) nanowires were synthesized using the traditional solid state reaction. X-ray diffraction experiment suggested the monoclinic structure (P2(1)/m), and crystal morphology analysis indicated that the band-like shape is the stable morphology. Two charge density wave (CDW) states were observed at around 140 K and 50 K, respectively, and the nonlinear effect was detected in the CDW states from the R-T and I-V measurements. The doped Fe atoms, as pinning centers, play an important role in the nonlinear properties of the CDW state. Electron diffraction and HRTEM experiments were carried out at different temperatures in order to investigate the structural features and their evolution. The sets of incommensurate modulation spots with modulation vector q1 - (h, k +/- 0.243, l) appeared below 145 K, and other sets of complex superstructure spots with modulation vector q2 - (h, k + 0.3, l + 1.3424), q3 - (h, k - 0.3137, 1.5685), q4 = (1/3, k, 1) and q5 = (0.5, 0.25, 0.5) were observed at [1 0 0] and [3 0 1] zone axis at about 20 K, respectively, suggesting the complex incommensurately modulated structures in this material.

Giant electrically tunable magnon transport anisotropy in a van der Waals antiferromagnetic insulator.

Anisotropy is a manifestation of lowered symmetry in material systems that have profound fundamental and technological implications. For van der Waals magnets, the two-dimensional (2D) nature greatly enhances the effect of in-plane anisotropy. However, electrical manipulation of such anisotropy as well as demonstration of possible applications remains elusive. In particular, in-situ electrical modulation of anisotropy in spin transport, vital for spintronics applications, has yet to be achieved. Here, we realized giant electrically tunable anisotropy in the transport of second harmonic thermal magnons (SHM) in van der Waals anti-ferromagnetic insulator CrPS4 with the application of modest gate current. Theoretical modeling found that 2D anisotropic spin Seebeck effect is the key to the electrical tunability. Making use of such large and tunable anisotropy, we demonstrated multi-bit read-only memories (ROMs) where information is inscribed by the anisotropy of magnon transport in CrPS4. Our result unveils the potential of anisotropic van der Waals magnons for information storage and processing.

High precision, low excitation capacitance measurement methods from 10 mK to room temperature.

Capacitance measurement is a useful technique in studying quantum devices, as it directly probes the local particle charging properties, i.e., the system compressibility. Here, we report one approach that can measure capacitance from mK to room temperature with excellent accuracy. Our experiments show that such a high-precision technique is able to reveal delicate and essential properties of high-mobility two-dimensional electron systems.

Aharonov-casher effect in Bi2Se3 square-ring interferometers.

Electrical control of spin dynamics in Bi(2)Se(3) was investigated in ring-type interferometers. Aharonov-Bohm and Altshuler-Aronov-Spivak resistance oscillations against a magnetic field, and Aharonov-Casher resistance oscillations against the gate voltage were observed in the presence of a Berry phase of π. A very large tunability of spin precession angle by the gate voltage has been obtained, indicating that Bi(2)Se(3)-related materials with strong spin-orbit coupling are promising candidates for constructing novel spintronic devices.

A simple and efficient route for preparing 2,3,5,6-tetraaminopyridine hydrochloride salt.

A simple and efficient route for preparing 2,3,5,6-tetraaminopyridine hydrochloride salt (TAP x 3HCl x H(2)O) was introduced in this paper. The title compound was synthesized, as usual, in two steps (nitration and hydrogenation) with a total yield of 90%. The use of an oleum and fuming nitric acid mixture in the nitration step improved the yield and purity of the intermediate product. A highly efficient hydrogenation using a H(2)/Pd/C/C(2)H(5)OH system was developed. The products were characterized by TG, IR, (1)H-NMR, (13)C-NMR, HPLC and elemental analysis.

Porous Pt-NiO x nanostructures with ultrasmall building blocks and enhanced electrocatalytic activity for the ethanol oxidation reaction.

Oxidized species on surfaces would significantly improve the electrocatalytic activity of Pt-based materials. Constructing three-dimensional porous structures would endow the catalysts with good stability. Here, we report a simple strategy to synthesize porous Pt-NiO x nanostructures composed of ultrasmall (about 3.0 nm) building blocks in an ethanol-water solvent. Structure and component analysis revealed that the as-prepared material consisted of interconnected Pt nanocrystals and amorphous NiO x species. The formation mechanism investigation revealed that the preformed amorphous compounds were vital for the construction of porous structure. In the ethanol oxidation reaction, Pt-NiO x /C exhibited current densities of 0.50 mA cmPt -2 at 0.45 V (vs. SCE), which were 16.7 times higher than that of a commercial Pt/C catalyst. Potentiostatic tests showed that Pt-NiO x /C had much higher current and better tolerance towards CO poisoning than the Pt/C catalyst under 0.45 V (vs. SCE). In addition, the NiO x species on the surface also outperformed an alloyed Ni component in the test. These results indicate that the Pt-NiO x porous nanomaterial is promising for use in direct ethanol fuel cells.

Influence of Carbon Deposits on the Cobalt-Catalyzed Fischer-Tropsch Reaction: Evidence of a Two-Site Reaction Model.

One of the well-known observations in the Fischer-Tropsch (FT) reaction is that the CH4 selectivity for cobalt catalysts is always higher than the value expected on the basis of the Anderson-Schulz-Flory (ASF) distribution. Depositing graphitic carbon on a cobalt catalyst strongly suppresses this non-ASF CH4, while the formation of higher hydrocarbons is much less affected. Carbon was laid down on the cobalt catalyst via the Boudouard reaction. We provide evidence that the amorphous carbon does not influence the FT reaction, as it can be easily hydrogenated under reaction conditions. Graphitic carbon is rapidly formed and cannot be removed. This unreactive form of carbon is located on terrace sites and mainly decreases the CO conversion by limiting CH4 formation. Despite nearly unchanged higher hydrocarbon yield, the presence of graphitic carbon enhances the chain-growth probability and strongly suppresses olefin hydrogenation. We demonstrate that graphitic carbon will slowly deposit on the cobalt catalysts during CO hydrogenation, thereby influencing CO conversion and the FT product distribution in a way similar to that for predeposited graphitic carbon. We also demonstrate that the buildup of graphitic carbon by 13CO increases the rate of C-C coupling during the 12C3H6 hydrogenation reaction, whose products follow an ASF-type product distribution of the FT reaction. We explain these results by a two-site model on the basis of insights into structure sensitivity of the underlying reaction steps in the FT mechanism: carbon formed on step-edge sites is involved in chain growth or can migrate to terrace sites, where it is rapidly hydrogenated to CH4. The primary olefinic FT products are predominantly hydrogenated on terrace sites. Covering the terraces by graphitic carbon increases the residence time of CH x intermediates, in line with decreased CH4 selectivity and increased chain-growth rate.

Synthesis of stable and low-CO2 selective ε-iron carbide Fischer-Tropsch catalysts.

The Fe-catalyzed Fischer-Tropsch (FT) reaction constitutes the core of the coal-to-liquids (CTL) process, which converts coal into liquid fuels. Conventional Fe-based catalysts typically convert 30% of the CO feed to CO2 in the FT unit. Decreasing the CO2 release in the FT step will reduce costs and enhance productivity of the overall process. In this context, we synthesize phase-pure ε(')-Fe2C catalysts exhibiting low CO2 selectivity by carefully controlling the pretreatment and carburization conditions. Kinetic data reveal that liquid fuels can be obtained free from primary CO2. These catalysts displayed stable FT performance at 23 bar and 235°C for at least 150 hours. Notably, in situ characterization emphasizes the high durability of pure ε(')-Fe2C in an industrial pilot test. These findings contribute to the development of new Fe-based FT catalysts for next-generation CTL processes.

Interconnected hierarchical NiCo2O4 microspheres as high-performance electrode materials for supercapacitors.

Herein, interconnected hierarchical NiCo2O4 microspheres (IH-NiCo2O4) were prepared via a solvothermal method followed by an annealing treatment. IH-NiCo2O4 possesses large tunnels and abundant mesopores, which are in favor of their applications in energy storage field. When employed as an electrode material for supercapacitors, IH-NiCo2O4 exhibits a high specific capacitance of 1822.3 F g-1 at a current density of 2 A g-1, an excellent rate property of 68.6% capacity retention at 20 A g-1, and an 87.6% specific capacitance retention of its initial value after 7000 cycles at a high current density of 10 A g-1, superior to those of IH-Co3O4. Furthermore, an optimal asymmetric supercapacitor (ASC) was also constructed with IH-NiCo2O4 as the positive electrode and graphene as the negative electrode. The ASC delivers a high energy density of 39.4 Wh kg-1 at a power density of 800 W kg-1. Even at a high power density of 8000 W kg-1, the energy density still reaches 27.2 Wh kg-1. Moreover, the ASC shows a good cycling stability with 80.1% specific capacitance retention after 5000 cycles at 6 A g-1. The excellent electrochemical performance of IH-NiCo2O4 makes it a promising electrode material in energy storage field.

An Investigation of the High Performance of a Novel Type of Benzobisoxazole Fiber Based on 3,3-Diaminobenzidine.

The mechanical and thermal properties of poly{2,6-diimidazo[4,5-b:4'5'-e] pyridinylene-1,4(2,5-dihydroxy) phenylene} (PIPD)-3,3-diaminobenzidine (DAB) fibers were analyzed. Compared to other types of benzimidazole fiber structures and properties, PIPD-DAB is distinguished by a unique combination of strength, tensile modulus, and thermal properties. The PIPD polymer was prepared from 2,3,5,6-tetra-aminopyridine (TAP) and 2,5-dihydroxyterephthalic acid (DHTA) in polyphosphoric acid (PPA). In order to enhance the tensile strength and modulus, a third comonomer, 3,3-diaminobenzidine (DAB), was incorporated into the PIPD molecular structure. The change in molecular structure was recorded using Fourier-transform infrared (FT-IR) spectroscopy, nuclear magnetic resonance (NMR) spectroscopy, and wide angle X-ray diffraction (WAXD). Compared to the PIPD fibers (average tensile strength of PIPD is 3.9 GPa, average tensile modulus of PIPD is 287 GPa), the tensile strength and modulus of PIPD-DAB increased to 4.2 and 318 GPa, respectively. In addition, the thermal decomposition temperature of the PIPD fibers is enhanced by 35 °C, due to the incorporated DAB. PIPD-DAB is a promising material for use under high tensile loads and/or high temperatures.