Effect of Pd additive on the activity of monolithic LaMnO3-based catalysts for methane combustion

When the perovskites are calcined at 750 °C, the incorporation of Pd into LaMnO₃ enhances the activity of the catalyst in methane combustion at temperatures below 750 °C upon substitution of 0.1 mol La with Pd, and at temperatures below 600 °C when Pd is substituted for 0.1–0.15 mol Mn. Monolith catalysts based on La_1−xPd_xMnO₃ (x = 0.1, 0.15) display a higher activity in methane combustion than do LaMn_1−xPd_xO₃-based catalysts, which is due to the higher Pd/(Pd + Mn + La) ratio. The activities of the two perovskite types increase when calcination temperature is raised from 650 to 800 °C. With the increase in calcination temperature, an increase in the Pd content and a decrease in the La content is observed on the surfaces (X-ray photoelectron spectroscopy (XPS)). The rise in the temperature of perovskite calcination to 850 °C produces sintering which leads to the lowering in both the Pd content on the surfaces and the specific surface areas (SSAs) of the perovskites and, consequently, decreases catalytic activity.     

Effect of washcoat modification with metal oxides on the activity of a monolithic Pd-based catalyst for methane combustion

The deposition of Ni, Co, Ce or Fe oxides onto the washcoat surface in the 0.5%Pd/Al₂O₃ catalyst enhances conversion of CH₄. Catalytic activity of the Pd-catalysts containing cobalt oxide depends on the incorporated amount of cobalt oxide and the method of incorporation. The highest activities were those of the 0.5%Pd/0.3%Co/Al₂O₃ and 1%Pd/0.3%Co/Al₂O₃ catalysts (cobalt oxide deposited onto the surface of Al₂O₃) and the 0.5%Pd/5%Co₃O₄–Al₂O₃ catalyst (mixed washcoat). Total SSA, Pd dispersion and Pd crystallite size in the x%Pd/y%Co/Al₂O₃ catalysts depend on the incorporated amount of PdO and cobalt oxide. Pd dispersion in the 1%Pd/Al₂O₃ catalyst increases from 4% to 20% upon deposition of 14 wt.% Co₃O₄ (by mass Al₂O₃) onto the Al₂O₃ surface (1%Pd/0.3%Co/Al₂O₃). This increase in Pd dispersion influence the increase in the activity of the 1%Pd/Al₂O₃ catalyst. On the surface of the 0.5%Pd/5%Co₃O₄–Al₂O₃ catalyst Pd occurs mainly in the form of PdO and displays considerable mobility under conditions of temperature variations—cyclically undergoing reduction and oxidation. At 500 °C, in vacuo, the reduction was irreversible and parallelled by the agglomeration of metallic Pd crystallites. At room temperature, cobalt occurred on the catalyst surface in the form of Co⁺² ions (CoAl₂O₄) and was reduced to Co⁰ at 500 °C (in vacuo). Up to 500 °C, the reduction of Co was reversible.     

Y802型恒温烘箱温控系统的模糊设计

对国产Y802型恒温烘箱温控系统作了分析，指出原采用的“电接式水银温度计检测—继电／接触器控制”系统存在温度控制偏差大的缺陷，提出以单片机控制系统替代原接触器控制系统，并采用模糊逻辑控制规则对烘箱温度实行控制的方案。利用Matlab系统仿真功能建立了以模糊逻辑控制器为核心的温控系统模型，并进行了仿真运行。结果证明，采用单片/拟模糊逻辑控制系统大大优于原系统。     

Size-controlled synthesis and photoluminescence of porous monolithic α-alumina

A modified polyacrylamide gel route is used to synthesize porous monolithic α-alumina. X-ray powder diffraction analysis indicates that the as-prepared samples are rhombohedral α-alumina phase, suggesting that high-purity α-alumina can be prepared by using different chelating agents and sintering at about 1150 °C. The scanning electron microscopic images show that the macropore size of the α-alumina samples is related to the chelating agent. The photoluminescence spectra show that a major emission band around 365 nm and a weaker side band located at 330 nm are observed when the excitation wavelength is 228 nm. Interestingly, the intensity of emission peak at 365 nm decreases with the decreasing pore size. The pore-forming and luminescence mechanisms of porous alumina have been discussed based on the experimental results.     

微机控制在提升机恒减速制动系统中的应用

重点对恒减速安全制动进行了分析,提出用以单片机为核心部件、采用ＰＩＤ参数自寻优控制的数字式电路对原有的恒减速模拟器件控制装置实施改造,从而较好地解决了原有系统存在的控制精度不高和调试复杂等问题。     

非接触双路激光检测仪研究

本文介绍一种非接触式检测大直径 (94—2 2 6mm)回转体工件的直径误差的双路激光扫描检测仪的工作原理及总体构成。该仪器采用双路激光扫描检测新技术 ,通过电子学理论及单片机技术进行误差分离和数据处理 ,以实现对大直径回转体件的精确测量     

Combustion of volatile organic compounds in two-component mixtures over monolithic perovskite catalysts

Activity of monolithic perovskite catalysts in oxidation of selected hydrocarbons and oxy-derivatives, oxidized individually and in two-component mixtures, as well as the reaction selectivity were investigated. One bulk perovskite (LaMn₂O₃) catalyst and two catalysts based on LaMn₂O₃ with addition of silver (25 at.%) coated on cordierite support were prepared for the study. The efficiency of oxy-derivatives oxidation was higher than that of hydrocarbon oxidation, but some by-products (first of all aldehydes) were detected in the flue gases. Addition of silver to the active phase improved catalyst activity and selectivity to CO₂ and water. The “mixture effect” on catalyst activity and selectivity depended on composition of the reaction mixture and the catalyst used. The presence of oxy-derivative in the reaction mixture inhibited oxidation of hydrocarbons. Toluene inhibited the process of oxy-derivatives conversion and increased the concentration of incomplete oxidation products.     

便携式微机控制风速测量仪

本文主要阐述一种便携式微机控制风速测量仪的主要功能,硬件系统结构和工作原理。这种风速测量仪以高性能的８７５１单片机为核心,由存储器和Ｉ／Ｏ接口电路等部件组成,各部件之间的信息传递采用总线结构形式,面板采用键盘操作各功能由程序控制,从而实现测量、数据记录、数据处理、综合分析等全自动化功能,是一种智能化仪表。     

电气化铁路接触网支撑杆实时计数系统

本文介绍了采用数字滤波和定距采样技术构成的电气化铁路输电线支撑杆实时计数系统。