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1.
CO_2由于热力学稳定性和动力学惰性,难以高效活化。采用并流沉淀法制备锆酸钡(BaZrO_3)催化剂并用于逆水煤气变换反应,结合物化表征和性能评价考察离子掺杂对催化活性、催化剂结构和还原性能的影响以及水热处理对催化剂结构和性能的影响。结果表明,过渡金属离子掺杂BaZrO_3催化剂产生晶格氧空位,提高CO_2转化率,以Mn离子掺杂的催化剂性能最好。晶格掺杂不会改变催化剂晶相结构,但增强晶格氧迁移能力,促进催化剂容易还原,进而显著提高逆变换催化活性。催化剂经水热处理可消除游离杂相,产物选择性提高至99.4%。优化条件下,Mn掺杂BaZrO_3催化剂上CO_2转化率大于48%,CO选择性大于99%,催化剂稳定性好,具有良好的应用前景。 相似文献
2.
Aiichiro Nagaki Yiyuan Jiang Hiroki Yamashita Naoshi Takabayashi Yusuke Takahashi Jun-ichi Yoshida 《化学工程与技术》2019,42(10):2113-2118
The lithiation of 5,5′‐dibromo‐2,2′‐bithiophene with one equivalent of an alkyllithium such as n‐BuLi or s‐BuLi was studied by varying the residence time in flow microreactors. With a short residence time, the product 2,2′‐bithiophene (3) derived from dilithiation was obtained preferentially and a significant amount of the starting material 5,5′‐dibromo‐2,2′‐bithiophene remained unchanged. An increase in the residence time caused a higher yield of the product 5‐bromo‐2,2′‐bithiophene derived from monolithiation with expense in the yields of 2,2′‐bithiophene and 5,5′‐dibromo‐2,2′‐bithiophene. The lithiation using MeLi gave the product 5‐bromo‐2,2′‐bithiophene preferentially even with a very short residence time. 相似文献
3.
Larry R. Falvello 《Crystallography Reviews》2020,26(3):117-140
This educational review postulates the importance of maintaining an adequate level of crystallographic education among structure-dependent scientists whose interests are not primarily in crystallography, at a time when automation and validation have made it possible to obtain high-quality structure analyses in many cases with a minimum of crystallographic background. The topics addressed are intended to form a second round of crystallographic education for a novice user whose first round involved hands-on experience with structure solution and an introduction to elementary concepts. The specific topics, chosen for their relevance as basic knowledge and their lack of emphasis in many formal treatments, are (1) crystallographic reference frames and the utility of the reciprocal cell in geometrical calculations; (2) the relationship between the two concepts that constitute our model of the crystal, namely the unit cell and the lattice; (3) the manner in which an atom is represented in concept and in practice; (4) the importance of interleaved symmetry elements required by the presence of additional symmetry on a lattice; (5) the harnessing of the natural properties of the crystalline state for the potential manipulation of properties of synthetic crystals; and (6) useful terminology for navigating a crystal structure. 相似文献
4.
5.
Sustainable agriculture has the potential to address some of the fundamental challenges facing agricultural practices in Africa especially in Sub-Saharan Africa (SSA). The agriculture sector plays an important role as the engine of economic growth in SSA. In this article, we ask the following key question: Can sustainable agriculture save Africa from poverty and food insecurity? To address this fundamental question, we examine and critique evidence of the benefits and challenges associated with the adoption of sustainable agricultural practices in Africa. Improving agricultural sustainability is fundamental to food security and poverty reduction, particularly in achieving elements of the sustainable development goals (SDGs) by 2030, but it will not solve all these problems alone. In consort, African governments and the international community must increase their efforts in tackling problems such as conflicts, civil war, political instability, and disease. Therefore, agricultural policy at the national, regional, and local levels and institutional reforms must be designed to benefit food security, poverty reduction, and income growth at the household level. 相似文献
6.
Sheng WANG Jun WANG Yingjie XU Weihong ZHANG Jihong ZHU 《Frontiers of Mechanical Engineering》2020,15(2):319-327
Frontiers of Mechanical Engineering - Lattice structures have numerous outstanding characteristics, such as light weight, high strength, excellent shock resistance, and highly efficient heat... 相似文献
7.
《Ceramics International》2020,46(9):13711-13723
Multi-track Ti-based wear-resistant composite coatings were fabricated on TC4 alloy surfaces using laser-clad TC4 + Ni45 + Co–WC mixed powders with different Y2O3 contents (0, 1, and 3 wt%). The microstructure, microhardness, and tribological properties of the coatings were characterised using X-ray diffraction, scanning electron microscopy, energy dispersive spectrometry, electron probe X-ray micro analyser, microhardness tester, and friction and wear testing apparatus. The results showed that the number of cracks on the coating surfaces gradually decreased with the addition of Y2O3 and that residual Co–WC powders existed in the coating subsurfaces. The phase composition of the coatings with different Y2O3 contents remained unchanged and was mainly composed of reinforcing phases of TiC, TiB2, Ti2Ni, and matrix α-Ti. With the addition of Y2O3, the coating microstructure was remarkably refined, the direction characteristic of the TiC dendrites obviously weakened, and the nucleation rate significantly increased. When the added Y2O3 was 3 wt%, a large amount of TiB2–TiC-dependent growth composite phases precipitated in the coating. The two-dimensional lattice misfit between (0001)TiB2 and (111)TiC was 0.912%, which indicated that TiB2 and TiC formed a coherent interface. When the amount of Y2O3 was increased, the microhardness of the coatings gradually decreased, and the wear volume of the coatings first increased and then decreased. Under the effect of the TiB2–TiC composite phases, the wear resistance of the 3 wt% Y2O3 coating was optimal. The 3 wt% Y2O3 coating friction coefficient was the lowest, and the wear mechanism was abrasive wear. 相似文献
8.
制备了具有不同疏水区宽度和面积分率的疏水-亲水间隔规则排列的组合表面。观测常压蒸汽在组合表面上冷凝时疏水区液滴的特性(液滴移除方式和最大液滴半径),利用格子Boltzmann方法模拟组合表面上凝液的运动。考察疏水区、亲水区宽度和表面过冷度对组合表面强化蒸汽冷凝传热的影响。利用滴状-膜状组合传热模型分析组合表面蒸汽冷凝传热性能的影响因素,并与实验结果比较。发现疏水区液滴自发地向亲水区定向迁移,精细设计的组合表面可以实现蒸汽滴状冷凝传热的强化,实验中强化因子可达1.20。疏水区宽度约为0.55 mm时组合表面的传热性能最大。表面过冷度越大,组合表面强化传热的效果越差,模型分析与实验结果吻合良好。 相似文献
9.
《中国有色金属学会会刊》2020,30(3):559-570
The formation of non-dendritic structures in the primary phase of an aluminum alloy solidified using low superheat pouring with a shearing field (LSPSF) machine was investigated by numerical simulation. The growth and motion of a dendrite during solidification was simulated by a combination of the lattice Boltzmann method and the phase field method. The simulation results indicated that enough shear flow helped homogenize the concentration fields, rotate crystals and altere microstructures from dendritic to non-dendritic. The interaction of grains was also discussed. A fragmentation criterion was established based on partial remelting of dendrite arms; fragmentation was enhanced by a strong shear flow and larger inclined angles. The simulation results were verified experimentally. 相似文献
10.
Channa Wang Ling Li Huihua Wang Tianpeng Qu Jun Tian Deyong Wang Zhenhui Kang 《加拿大化工杂志》2020,98(8):1784-1793
Cost-effective catalysts for hydrogen evolution reaction (HER) are attractive for sustainable production of H2 fuel. Herein, a series of tunable Ni/Fe-Mo carbide catalysts have been synthesized via a sol-gel method coupling with a subsequent high temperature carbonization process. The amount of nickel and iron was tuned in the Mo7/C precursors, accomplishing a favourable performance of noble-metal-free electrocatalysts for HER. As expected, the designed Ni10Fe4Mo7/C catalyst displays an enhanced catalytic activity toward hydrogen production with an ultralow overpotential (η10 = 110 mV) and striking kinetics (ηonset = 58 mV, k = 54 mV · dec−1) in the alkaline electrolyte (1 M KOH), which are comparable to those of the commercial 20% Pt/C catalyst. Such excellent performance of Ni10Fe4Mo7/C could be attributed to the high intrinsic activities of Ni-based alloys (NiMo4) and Mo2C, as well as to the lattice contraction in the Mo2C unit cell, in accordance with its high electrochemical surface area (~133 m2 · g−1) and low charge-transfer resistance (~31.5 Ω) for the associated electrode. 相似文献