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71.
A vacuum-annealed La0.6Ca0.4CoO3−x was consecutively oxygenated in air at temperatures decreasing from 800 to 100 °C, and its electrocatalytic activities for oxygen reduction and evolution were then measured as a function of the oxygenation temperature. The valence of Co cation, changing between +2 and +3, was found susceptible to annealing either in vacuum or air. The catalytic activities initially decrease monotonically as the oxygenation temperature was decreased from 800 to 300 °C, as a result of increasing oxygen content, and then rise abruptly with the oxygen reduction activity reaching a maximum at 200 °C and the oxidation activity at 150 °C. X-ray photoelectron spectroscopy analysis indicated that the enhancements by the low-temperature oxygenation involved increased OH coverage and less charged cations at surface. The results clearly reveal the importance of the post-calcination annealing process for optimizing the performance of La0.6Ca0.4CoO3−x in air electrode applications. 相似文献
72.
Concrete interlocking blocks (CIBs) are utilized in a variety of commercial, municipal, and industrial applications. Superior engineering properties, low maintenance, ease of placement and removal, reuse of original blocks, aesthetic appeal, and immediate availability are the primary reasons for choosing concrete block pavement over other paving surfaces. It is a common practice to pigment building materials, such as mortar, concrete pavers, concrete roof tiles, and prefabricated concrete products; CIBs are colored using iron oxide pigments. This article presents experimental results detailing the properties of CIBs dyed with pigments. The results of these experiments are as follows: Because the particles of iron oxide pigments are finer than those of brown iron oxide, interlocking blocks mixed with the former acquired higher color strength than with the latter. Additional analysis determined a definite relationship between the flexural strength and the absorption ratio of pigment-dyed blocks; the correlation coefficient (R2) of interlocking blocks at 91 days was .90. It is suggested that if iron oxide pigments are to be used to color CIBs, the pigment-to-cement ratio should be below 4%. 相似文献
73.
74.
采用浸渍法制备了Nb2O5/α-A l2O3催化剂(简称催化剂)并用于环氧乙烷水合制乙二醇的反应,通过控制α-A l2O3载体中致孔剂的含量来调变载体的孔径、孔分布及比表面积;采用吡啶吸附红外光谱、氨程序升温脱附法研究了载体的比表面积及孔径对催化剂酸性及反应性能的影响。实验结果表明,产物的选择性受扩散因素及催化剂酸性的影响,而催化剂的酸量、酸密度可以通过载体的孔径及比表面积的变化加以调控。比表面积较小及孔径较大的载体对催化剂催化环氧乙烷水合制乙二醇的反应较为有利。当载体的比表面积小于0.80m2/g、孔径为4.00~8.00μm时,在反应温度160℃、反应压力1.5M Pa、n(H2O)∶n(EO)=22、液态空速25h-1的条件下,环氧乙烷的转化率大于99.8%,乙二醇的选择性超过89.9%。 相似文献
75.
76.
溶剂对环氧乙烷催化水合制乙二醇的影响 总被引:1,自引:1,他引:0
研究了NY催化剂催化环氧乙烷水合制乙二醇(EG)过程中,溶剂、催化剂添加量和水与环氧乙烷的摩尔比(简称水比)对EG选择性的影响。实验结果表明,以丙三醇作为溶剂使催化剂进行循环,能提高EG的选择性,效果好于以生成的EG作为溶剂循环催化剂。催化剂添加量、水比和溶剂添加量对EG选择性具有较大影响,其中溶剂添加量对EG选择性的影响最显著。在低水比(1.0~4.0)条件下,EG质量分数小于30%、催化剂质量分数大于7.2%时,EG选择性稳定在95.63%~97.92%,平均值为96.80%,此结果对于进一步降低EG合成工艺的能耗具有指导意义。 相似文献
77.
G. Murali Dhar B. N. Srinivas M. S. Rana Manoj Kumar S. K. Maity 《Catalysis Today》2003,86(1-4):45-60
Support effects form important aspect of hydrodesulfurization (HDS) studies and mixed oxide supports received maximum attention in the last two decades. This review will focus attention on studies on mixed oxide supported Mo and W catalysts. For convenience of discussion, these are divided into Al2O3 containing mixed oxide supports, TiO2 containing mixed oxide supports, ZrO2 containing mixed oxide supports and other mixed oxide supports containing all the rest. TiO2 containing mixed oxides received maximum attention, especially TiO2–Al2O3 supported catalysts. A brief discussion about their prospects for application to ultradeep desulfurization is also included. An overview of the available literature with emphasis on research carried out in our laboratory form the contents of this publication. 相似文献
78.
聚丙烯酰胺/氧化石墨纳米复合材料的研究 总被引:4,自引:0,他引:4
氧化石墨具有良好的层状结构,其层间具有丰富的官能团,能与有机聚合物形成插层纳米复合材料进而改善材料的性能.采用层离吸收-原位聚合法制备了聚丙烯酰胺/氧化石墨纳米复合材料,并采用XRD、HREM及DSC等对其结构和性能进行了表征。结果表明,聚丙烯酰胺与氧化石墨两者之间存在着较强的相互作用,材料的玻璃化转变温度得到提高,层离吸收-原位聚合法是获得聚丙烯酰胺/氧化石墨层纳米复合材料的有效途径,聚丙烯酰胺在氧化石墨中存在着多种排列方式,不同层间距(1.6nm和2.8nm)的聚丙烯酰胺/氧化石墨纳米复合结构同时存在。 相似文献
79.
80.
Nitric oxide reduction and carbon monoxide oxidation over carbon-supported copper-chromium catalysts 总被引:1,自引:0,他引:1
S. Stegenga R. van Soest F. Kapteijn J. A. Moulijn 《Applied catalysis. B, Environmental》1993,2(4):257-275
Carbon supported copper-chromium catalysts are shown to be very active for both the reduction of nitric oxide with carbon monoxide and the oxidation of carbon monoxide with oxygen. Mixed copper-chromium oxide active phases have good activity in the simultaneous removal of nitric oxide and carbon monoxide from exhaust gases. The influence of several catalyst variables has been investigated. The activity per volume of catalyst increases with increasing loading, while the intrinsic activity shows a maximum around C/M=100−50. An optimum catalyst for nitric oxide reduction and carbon monoxide oxidation has a copper/chromium ratio of 2/1. The apparent activation energy for the carbon monoxide oxidation over carbon supported copper-chromium catalysts is 77 kJ/mol, suggesting that the Cu---O bond rupture is the rate-limiting process. The reduction of nitric oxide takes place at higher temperatures. Since all catalysts have a low selectivity for molecular nitrogen formation at lower temperatures, the dissociation of nitric oxide is probably rate determining, resulting in a slightly reduced catalyst system. In an excess of carbon monoxide the reaction is first-order in nitric oxide and zero-order in carbon monoxide. Moisture inhibits the reaction by reversible competitive adsorption, whereas carbon dioxide does not. Oxygen completely inhibits the reduction of nitric oxide due to the more rapid reoxidation of the catalytic sites compared to nitric oxide. Therefore, the reduction of nitric oxide takes place only when all oxygen has been converted and, hence, is shifted to higher temperatures. As a possible consequence, the production of nitrous oxide is reduced. Nitric oxide and molecular oxygen react preferentially with carbon monoxide, so, in an excess of oxidizing component, gasification of the carbon support occurs at higher temperatures after carbon monoxide has been completely consumed. 相似文献