The direct synthesis of dimethyl ether from syngas over hybrid catalysts with sulfate-modified γ-alumina as methanol dehydration components

A series of γ-Al₂O₃ samples modified with various contents of sulfate (0–15 wt.%) and calcined at different temperatures (350–750 °C) were prepared by an impregnation method and physically admixed with CuO–ZnO–Al₂O₃ methanol synthesis catalyst to form hybrid catalysts. The direct synthesis of dimethyl ether (DME) from syngas was carried out over the prepared hybrid catalysts under pressurized fixed-bed continuous flow conditions. The results revealed that the catalytic activity of SO₄²⁻/γ-Al₂O₃ for methanol dehydration increased significantly when the content of sulfate increased to 10 wt.%, resulting in the increase in both DME selectivity and CO conversion. However, when the content of sulfate of SO₄²⁻/γ-Al₂O₃ was further increased to 15 wt.%, the activity for methanol dehydration was increased, and the selectivity for DME decreased slightly as reflected in the increased formation of byproducts like hydrocarbons and CO₂. On the other hand, when the calcination temperature of SO₄²⁻/γ-Al₂O₃ increased from 350 °C to 550 °C, both the CO conversion and the DME selectivity increased gradually, accompanied with the decreased formation of CO₂. Nevertheless, a further increase in calcination temperature to 750 °C remarkably decreased the catalytic activity of SO₄²⁻/γ-Al₂O₃ for methanol dehydration, resulting in the significant decline in both DME selectivity and CO conversion. The hybrid catalyst containing the SO₄²⁻/γ-Al₂O₃ with 10 wt.% sulfate and calcined at 550 °C exhibited the highest selectivity and yield for the synthesis of DME.     

Defect mitigation using d-penicillamine for efficient methylammonium-free perovskite solar cells with high operational stability

Trap-dominated non-radiative charge recombination is one of the key factors that limit the performance of perovskite solar cells (PSCs), which was widely studied in methylammonium (MA) containing PSCs. However, there is a need to elucidate the defect chemistry of thermally stable, MA-free, cesium/formamidinium (Cs/FA)-based perovskites. Herein, we show that d-penicillamine (PA), an edible antidote for treating heavy metal ions, not only effectively passivates the iodine vacancies (Pb²⁺ defects) through coordination with the –SH and –COOH groups in PA, but also finely tunes the crystallinity of Cs/FA-based perovskite film. Benefiting from these merits, a reduction of non-radiative recombination and an increase in photoluminescence lifetime have been achieved. As a result, the champion MA-free device exhibits an impressive power conversion efficiency (PCE) of 22.4%, an open-circuit voltage of 1.163 V, a notable fill factor of 82%, and excellent long-term operational stability. Moreover, the defect passivation strategy can be further extended to a mini module (substrate: 4 × 4 cm², active area: 7.2 cm²) as well as a wide-bandgap (∼1.73 eV) Cs/FA perovskite system by delivering PCEs of 16.3% and 20.2%, respectively, demonstrating its universality in defect passivation for efficient PSCs.

Iodine vacancy defects in MA-free perovskite are effectively passivated through the interaction between Pb²⁺ and the functional groups in d-penicillamine, resulting in an impressive efficiency of 22.4% along with excellent operational stability.     

Design and Synthesis Strategies: 2D Materials for Electromagnetic Shielding/Absorbing

Two-dimensional (2D) materials possess special physical and chemical properties. They have been proved to have potential application advantage in the microwave absorption (MA) and electromagnetic interference (EMI) shielding. Particularly, they exhibit positive shielding and absorbing response to EMI. Here, the research progress of preparation, electromagnetic performance and microwave shielding/absorbing mechanisms of 2D composite materials are introduced. Effective preparation routes including introducing heteroatoms, constructing unique structures and 2D composite materials are described. Furthermore, the application prospects and challenges for the development of novel EMI materials are expatiated.     

分子筛硅／铝比对Cu-ZnO-Al2O3／HMCM-22催化合成二甲醚反应性能的影响

以六亚甲基亚胺为模板剂,采用动态水热晶化法合成了不同硅/铝比的HMCM-22分子筛,并以其为甲醇脱水活性组分与铜基甲醇合成活性组分(Cu-ZnO-Al2O3)组成双功能催化剂,在连续流动加压固定床微型反应器上考察了其对合成气直接制二甲醚反应的催化性能. 结果表明,随着HMCM-22分子筛硅/铝比的增大, CO转化率变化不大,但CO2和烃类副产物的生成量逐渐减少,从而导致目的产物二甲醚的选择性和收率均逐渐升高. 氨程序升温脱附和吡啶吸附红外光谱表征结果表明,随着分子筛硅/铝比的增大, HMCM-22分子筛的酸中心的数量逐渐减少.     

聚磷酸铵的疏水改性及聚丙烯阻燃性能

首先以γ-氨丙基三乙氧基硅烷(KH550)对聚磷酸铵(APP)进行表面化学修饰,然后用水解后的正硅酸四乙酯在其表面引发原位聚合,最后用十七氟癸基三乙氧基硅烷(氟硅烷)进行外表面修饰,制备了疏水聚磷酸铵(M-APP).M-APP的静态接触角为134°,表明M-APP具有很好的疏水性.通过傅里叶变换红外光谱(FTIR)和X射线光电子能谱(XPS)对M-APP的结构及表面元素进行分析,结果表明,M-APP即为目标产物.将M-APP与三嗪成炭发泡剂(CFA)以质量比4∶1复配制备改性膨胀型阻燃剂(M-APP/CFA),并添加到聚丙烯(PP)中,制备阻燃PP(PP/M-APP/CFA).通过极限氧指数(LOI)和垂直燃烧(UL-94)研究了其阻燃性能,用热重分析(TGA)研究了材料的热降解行为,通过耐水测试研究了耐水性能,通过拉伸、弯曲和冲击强度研究了材料的力学性能,通过扫描电子显微镜(SEM)研究了改性膨胀型阻燃剂与聚合物的相容性.结果表明,当m IFR的添加量为23%时,PP/M-APP/CFA通过UL-94 V-0级,LOI值达到30.8%,且经过耐水测试后,依然能通过UL-94 V-0级,PP/M-APP/CFA的失重率仅为0.92%.在相同实验条件下,由APP制备的PP/M-APP/CFA材料在耐水测试后UL-94测试无级别,失重率达2.45%,表明APP的表面疏水改性大大提高了PP/M-APP/CFA材料的耐水性能.M-APP/CFA的加入提高了材料的热稳定性及成炭性能,燃烧时形成的膨胀炭层能很好地保护内部材料的降解和燃烧,从而提高了材料的阻燃性能.APP的改性提高了M-APP/CFA与PP的相容性,从而提高了材料的力学性能.     

Improvement of chiral stationary phases based on cinchona alkaloids bonded to crown ethers by chiral modification

To improve the chiral recognition capability of a cinchona alkaloid crown ether chiral stationary phase, the crown ether moiety was modified by the chiral group of (1S, 2S)‐2‐aminocyclohexyl phenylcarbamate. Both quinine and quinidine‐based stationary phases were evaluated by chiral acids, chiral primary amines and amino acids. The quinine/quinidine and crown ether provided ion‐exchange sites and complex interaction site for carboxyl group and primary amine group in amino acids, respectively, which were necessary for the chiral discrimination of amino acid enantiomers. The introduction of the chiral group greatly improved the chiral recognition for chiral primary amines. The structure of crown ether moiety was proved to play a dominant role in the chiral recognitions for chiral primary amines and amino acids.     

氢氟酸后处理对Silicalite-1催化环己酮肟气相Beckmann重排反应性能的影响

 研究了氢氟酸后处理对 silicalite-1 催化环己酮肟气相Beckmann重排反应性能的影响. 结果表明,经适当浓度的氢氟酸溶液处理后,催化剂的选择性和稳定性都明显改善. 其中, silicalite-1 原粉先经硝酸铵预处理后再进行氢氟酸后处理所得到的催化剂催化性能最好,反应53 h后环己酮肟的转化率仍保持在96%左右,己内酰胺的选择性高达96.1%. XRD, FT-IR和 29Si MAS NMR的结果表明,较高的具有氢键相互作用的硅羟基与孤立硅羟基的比例值对环己酮肟气相Beckmann重排反应有利,同时, silicalite-1 表面硅原子的排布方式对该反应也有重要影响.     

基于改进卷积神经网络的数控机床旋转轴热误差建模方法

为对五轴数控机床旋转轴的热误差进行更精确地预测,解决变工况条件下预测精度不佳与热误差数据获取困难的问题,提出了基于改进卷积神经网络的热误差建模方法.采用激光干涉仪与热成像仪采集不同温度下的角度定位误差与热图像,对热误差进行傅里叶函数拟合,将预测目标由不同角度下的热误差转变为拟合函数参数.在VGG网络模型架构上,引入SKNet注意力机制,以提高模型对变工况下的热图像特征提取水平,并采用全局平均池化代替全连接层,以改善过拟合情况.将建立的模型用于热误差预测,结果表明,旋转轴热误差预测RMSE在升温状态下为8.36″,降温条件下为9.57″,预测精度达90%以上,优于普通卷积神经网络模型.结果证实了所提方法在旋转轴热误差建模中的有效性.     

Strain-Gradient-Induced Modulation of Carrier Density and Mobility at the LaAlO3/SrTiO3 Heterointerface

A strain gradient induced by mechanical bending on a SrTiO₃ substrate is demonstrated, and has a pronounced influence on the carrier density and mobility of the interfacial 2D electron gas at the LaAlO₃/SrTiO₃ heterointerface. Tensile and compressive strain gradients represent two states of upward and downward bending. Under the tensile strain gradient, the carrier density decreases and the mobility has about 200% increase. Conversely, under the compressive strain gradient, the mobility decreases and the carrier density increases by up to 107%. These results demonstrate a range of opportunities to modulate the carrier density and mobility at oxide heterointerface and open up a promising way for further research on application of oxide devices.     

十二烷基硫酸钠辅助制备高电容性能多孔碳

本工作通过一步水浴法制备高氮/氧含量密胺树脂(MF),引入阴离子型表面活性剂十二烷基硫酸钠(SDS)改变聚合物的反应历程,使进入SDS胶束中的三聚氰胺与甲醛在盐酸催化条件下进行聚合反应,高温碳化后成功制备MF衍生多孔碳材料.对MF衍生多孔碳材料分别进行了扫描电镜、比表面积等表征,结果表明,其具有多孔互穿网络结构,比表面...