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The effects of various alkali metal promoters on the structure–performance relationship of cobalt–manganese (CoMn) catalysts for the Fischer–Tropsch synthesis (FTS) reaction have been investigated. The electronic promotion effects are correlated with the ionic potential (IP) of the alkali metals, which represents their electronic polarizability. The presence of alkali metal promoters in the CoMn catalysts is beneficial for the formation and stabilization of the Co2C phase. With an increase in the IP of the alkali metal promoters, the active phase was found to transition from Co2C nanospheres to Co2C nanoprisms and then to a mixture of fcc Co0 and Co2C nanospheres. In addition, the catalytic performance also changed with the transition in the active phase. For the Co2C nanospheres, high CH4 selectivity and low activity were observed. A promising catalytic performance for Fischer–Tropsch to olefins (FTO) with low CH4 selectivity and high C2–4= selectivity was achieved for the Co2C nanoprisms. However, low C2–4= selectivity with high activity was found for a mixture of fcc Co0 and Co2C nanospheres. It is suggested that the alkali metal promoters in the CoMn catalysts have two different promotion effects that are enhanced with IP: (1) the electronic effect to enhance the CO dissociation probability and benefit the formation of Co2C and (2) the facet stabilization effect to stabilize the Co2C nanoprisms with specific exposed (101) and (020) facets under the FTO reaction conditions.

The Fischer–Tropsch to olefins (FTO) reaction over Co2C catalysts is structure-sensitive, as the catalytic performance is strongly influenced by the surface structure of the active phase. The exposed facets determine the surface structure, and it remains a great challenge to precisely control the particle morphology of the FTO active phase. In this study, the controlling effect of the Mn promoter on the final morphology of the Co2C nanoparticles for the FTO reaction was investigated. The unpromoted catalyst and several promoted catalysts with Ce, La, and Al were also studied for comparison. For the Mn-promoted catalysts, the combination method of the Co and Mn components plays a crucial role in the final morphology of Co2C and thus the catalytic performance. For the CoMn catalyst prepared by coprecipitation, Co2C nanoprisms with specifically exposed facets of (101) and (020) can be obtained, which exhibit a promising FTO catalytic performance with high C2–4= selectivity, low methane selectivity, and high ...

A series of Co/SiO2 catalysts with different sodium (Na) loadings (0, 0.1, 0.2, 0.5 and 1 wt%) were prepared and evaluated for Fischer-Tropsch reaction to study the effect of Na on the catalyst structure and catalytic performance. The addition of Na was found to decrease the catalytic activity and hydrocarbon selectivity, but increase CO2 selectivity due to the enhanced WGS activity. The addition of Na also resulted in higher selectivity to oxygenates (alcohols and aldehydes) and O/P ratio as well as the shift of hydrocarbons to lower carbon numbers. Structure characterization revealed a decrease in the surface area and particles size for the calcined samples with the addition of Na. Co2C was formed during the reaction process for the Na-promoted catalysts. As a result, a new Co/Co2C bifunctional active sites were generated for oxygenates formation leading to increasing oxygenates selectivity. In addition, the Co2C nanoparticles alone may also act as dual active sites for oxygenate formation at high reaction pressure over the promoted catalysts with high Na loading.

The effects of a sodium (Na) promoter on the catalytic performance of cobalt-manganese (CoMn) catalysts for Fischer–Tropsch to olefin (FTO) reactions were investigated. For the sample without Na, Co0 was found to be the active phase for the traditional Co-based Fischer–Tropsch reaction with low CO2 selectivity. The olefin/paraffin (O/P) ratio was found to be low with a C2–4= selectivity of only 15.4 C%. However, with the addition of Na, cobalt carbide (Co2C) quadrangular nanoprisms with the (101) and (020) facets exposed were formed. The Co2C nanoprisms displayed a high C2–4= selectivity (54.2 C%) as well as a low methane selectivity (5.9 C%) under mild reaction conditions. The O/P ratio for C2–4 reached 23.9, and the product distribution deviated greatly from the classical Anderson–Schulz–Flory (ASF) distribution. Co2C nanoprisms were considered to be an effective FTO active phase with strong facet effects. The Na promoter played a key role in the evolution of the FTO catalysts. The addition of Na, which...

Fast radio bursts (FRBs) are millisecond-duration radio transients of unknown origin. Two possible mechanisms that could generate extremely coherent emission from FRBs invoke neutron star magnetospheres or relativistic shocks far from the central energy source. Detailed polarization observations may help us to understand the emission mechanism. However, the available FRB polarization data have been perplexing, because they show a host of polarimetric properties, including either a constant polarization angle during each burst for some repeaters or variable polarization angles in some other apparently one-off events. Here we report observations of 15 bursts from FRB 180301 and find various polarization angle swings in seven of them. The diversity of the polarization angle features of these bursts is consistent with a magnetospheric origin of the radio emission, and disfavours the radiation models invoking relativistic shocks., Published online in Nature on 29 Oct, 2020

Replacement of the cables that have reached the designed operation period is seriously concerned. The effect of annealing is discussed in this paper, and a possible method for considering the reusing of retired cables is presented. XLPE samples were obtained from two retired 110 kV cables and their spare cable by a coaxial cutting method. Firstly, the samples were annealed at 85, 90, 95 and 100°C. Then, the differential scanning calorimetry (DSC) and DC current were measured. The analysis was mainly conducted by watching the annealing temperature dependence of thermal performance and DC current. The DSC results revealed that the crystallinity, melting point, and lamellar thickness changed monotonously as the annealing temperature increased from 85 to 95°C, and the highest values were observed. When the annealing temperature reached 100 °C, these quantities changed the opposite trend. Similarly, the change in DC current showed a same trend as the DSC results, the smallest value of current appeared as the sample annealed at 95°C. Importantly, annealing at 95 °C did not result in further degradation of these samples but morphology and electric performance improvement.

A novel synthetic route to the layered material PLS-4 has been developed using amorphous silica as the silica source and ethyldimethylethanolammonium fluoride as the organic structure-directing agent. This reaction can proceed under high concentration conditions utilizing quaternary ammonium fluoride salt rather than ammonium fluoride or hydrofluoric acid. By introducing aluminum, alkali metal and alkaline earth metal into the aforementioned system, three new morphologies have been obtained. Products were fully characterized using powder X-ray diffraction (XRD), scanning electron microscopy (SEM), and nitrogen adsorption analyses.

采用高速摄影术准确记录聚焦脉冲Nd:YAG 激光水下诱导空化泡动态变化进程, 同时采用针式水听器探测空泡闭合或等离子体膨胀时辐射的冲击波信号. 实验结果表明, 当针式水听器端面和聚焦点间距逐渐减小时, 相同实验条件下, 探测到的声学信号个数增多且信号强度增强. 激光脉冲结构、能量、脉宽等激光参数直接决定单个激光脉冲诱导空泡个数、形貌以及等离子体膨胀和空泡闭合时辐射的声学信号特性. 实验结果可为短脉冲激光在临床医学上的运用提供理论与实践支持.

Two-dimension and three-dimension topography of pulsed lasers ablation of tissues were scanned by means of optical coherent microscopy,in order to analyze the ablation characteristics of pulsed Erbium:YAG lasers for hard biological tissues.Experimental results indicate that under the same laser parameters,ablation efficiency for gall-stone is higher than that for urinary stone.The higher the intensities of pulsed lasers are,the higher the ablation efficiency will be for both gall-stone and urinary stone.The higher ablation efficiency mainly embodies that wider surface diameter,deeper height,and bigger volume for craters will be obtained.Measurements for stone craters using the optical coherent microscopy are higher by about one order than those using the optical coherent tomography.Optical coherent microscopy system can contribute to quantitatively measure hard tissues irradiated by pulsed lasers much better than optical coherent tomography system.

A method for preparing a SiC coating on carbon fibers is presented. The SiC coating was generated from the reaction of silicon monoxide (SiO) with a pyrolytic carbon (PyC) layer deposited on the fibers. The influence of holding time on the microstructure of the SiC layer was discussed. The oxidation behaviors of the uncoated and SiC coated carbon fibers were compared. The formation mechanism of the SiC coating was evaluated. With increased reaction time, the SiC coating becomes thicker and its surface becomes rough. The oxidation resistance of the carbon fiber was improved by the SiC coating. The initial oxidation temperature of the SiC coated carbon fiber is about 200 °C higher than that of the uncoated carbon fiber. The growth of the SiC coating is mainly attributed to the indirect reactions of SiO with PyC in the SiO/SiC/C system, in which silicon is considered a critical intermediate product.