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The coupling of reaction and diffusion between neighboring active sites in the catalyst pore leads to the spatiotemporal fluctuation in component concentration, which is very important to catalyst performance and hence its optimal design. Molecular dynamics simulation with hard-sphere and pseudo-particle modeling has previously revealed the non-stochastic concentration fluctuation of the reactant/product near isolated active site due to such coupling, using a simple model reaction of A → B in 2D pores. The topic is further developed in this work by studying the concentration fluctuation due to such coupling between neighboring active sites in 3D pores. Two 3D pore models containing an isolated active site and two adjacent active sites were constructed, respectively. For the isolated site, the concentration fluctuation intensifies for larger pores, but the product yield decreases, and for a given pore size, the product yield reaches a peak at a certain reactant concentration. For two neighboring sites, their distance (d) is found to have little effect on the reaction, but significant to the diffusion. For the same reaction competing at both sites, larger d leads to more efficient diffusion and better overall performance. However, for sequential reactions at the two sites, higher overall performance presents at a smaller d. The results should be helpful to the catalyst design and reaction control in the relevant processes. 相似文献
5.
Yuping Ji Kaixin Song Shiyu Zhang Zhilun Lu Ge Wang Linhao Li Di Zhou Dawei Wang Ian M. Reaney 《Journal of the European Ceramic Society》2021,41(1):424-429
Dense (1-x)wt%CaSnSiO5-xwt%K2MoO4 (CSSO-KMO) composite ceramics were fabricated by the cold sintering process at 180 °C under 400 MPa for 60 min. X-ray diffraction, Energy dispersive X-ray and Raman spectroscopy confirmed that CSSO and KMO coexisted without intermediate phases. As KMO weight fraction increased, relative permittivity (εr) and temperature coefficient of resonant frequency (τf) decreased and the microwave quality factor (Q×f, where f is resonant frequency) increased. Near-zero τf (-0.5 ppm/°C) was obtained for 65 wt%CSSO-35 wt%KMO with εr ~ 9.2 and Q×f ~ 6240 GHz. No chemical reaction between ceramic composites and silver was observed, demonstrating potential for cofiring with Ag-paste. A prototype antenna was fabricated from 65 wt%CSSO-35 wt%KMO composite ceramic with a bandwidth of 144 MHz @ -10 dB, a gain of 5.7 dBi and a total efficiency of 88.4 % at 5.2 GHz, suitable for 5 G mobile communication systems. 相似文献
7.
介绍了采用变温吸附技术对氯乙烯进行干燥脱水的工艺流程及运行效果,阐述了变温吸附装置运行过程中出现的问题及相应的解决方法。 相似文献
8.
提出了基于分区协调耦合推进的翼面热颤振时域研究方法,其中气动力和气动热采用有限体积法求解,且流场空间离散采用AUSM+格式,而结构温度场采用有限元法求解。采用模态叠加法进行结构瞬态响应的求解,在耦合面上采用基于虚拟空间的插值方法进行耦合变量的传递。研究了高超声速翼面的热颤振问题,获得了不同马赫数下的翼面温度场分布。根据“频率重合理论”获得了热环境下翼面一阶弯曲和一阶扭转频率的相互靠近导致了翼面临界颤振速度下降的结论。 相似文献
9.
Jincheng Yu Yabin Chang Ewa Jakubczyk Bing Wang Feridoon Azough Robert Dorey Robert Freer 《Journal of the European Ceramic Society》2021,41(9):4859-4869
Ca3Co4O9 is a promising p-type thermoelectric oxide material having intrinsically low thermal conductivity. With low cost and opportunities for automatic large scale production, thick film technologies offer considerable potential for a new generation of micro-sized thermoelectric coolers or generators. Here, based on the chemical composition optimized by traditional solid state reaction for bulk samples, we present a viable approach to modulating the electrical transport properties of screen-printed calcium cobaltite thick films through control of the microstructural evolution by optimized heat-treatment. XRD and TEM analysis confirmed the formation of high-quality calcium cobaltite grains. By creating 2.0 at% cobalt deficiency in Ca2.7Bi0.3Co4O9+δ, the pressureless sintered ceramics reached the highest power factor of 98.0 μWm?1 K-2 at 823 K, through enhancement of electrical conductivity by reduction of poorly conducting secondary phases. Subsequently, textured thick films of Ca2.7Bi0.3Co3.92O9+δ were efficiently tailored by controlling the sintering temperature and holding time. Optimized Ca2.7Bi0.3Co3.92O9+δ thick films sintered at 1203 K for 8 h exhibited the maximum power factor of 55.5 μWm?1 K-2 at 673 K through microstructure control. 相似文献
10.
通过对下肢3 个关节步态曲线建立具有共性控制点的数学模型,提出了以个体的局部形状参数作为区别同一关节中不同曲线的方法.实验采用Perception Neuron 动作捕捉系统,对正常组10 名健康男性青年,验证组2 名健康和3 名处于不同康复期的右腿踝关节损伤男性青年在正常步速下的步态数据进行实验测量以获得髋关节、膝关节和踝关节的上下位移轨迹曲线,并计算得出正常组步态曲线的局部形状参数作为判别步态正常与否的参考调整范围.经分析,验证组中健康被试者的局部形状参数大多属于该范围,而恢复较差的病人参数大多超出该范围,表明该参数化方法可有效辨别步态曲线差异,此外还可对康复评价的方法提供依据. 相似文献