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81.
The kinetics of the methanation of carbon dioxide was investigated using an alumina supported Ni-La2O2 catalyst in a differential and integral reactor. In the differential reactor the molar ratio of H2 to CO2 was varied from 0.6 to 30. In the integral reactor the rates were measured with up to 90% conversion. Both reactor tests were carried out at temperatures between 513 and 593 K. The experimental results were described by a Langmuir-Hinshelwood type equation. The kinetics can be explained by assuming equilibrium of dissociative carbon dioxide and hydrogen adsorption, and assuming hydrogenation of surface carbon as the rate determining step. 相似文献
82.
Phosphorus modification of ZSM-5 leads to extra framework P5+ and probably incorporation of +3 valence state of P in the framework. The resulting system has increased Brønsted acidity. Theoretical calculations also favour the postulate that phosphorus in +3 valence state can be incorporated into the lattice. 相似文献
83.
Mixed oxide catalyst prepared by co-precipitating magnesium oxide and calcium oxide showed an excellent activity for the oxidative coupling of methane. The high performances were presumed to arise from the high basicity of the mixed oxide. 相似文献
85.
Amorphous anodic titania, stabilised by incorporation of silicon species, is shown to grow to high voltages on sputter-deposited, single-phase Ti-Si alloys during anodizing at a constant current density in ammonium pentaborate electrolyte. The films comprise two main layers, with silicon species confined to the inner layers. An amorphous-to-crystalline transition occurs at ∼60 V on the Ti-6 at.% Si alloy, while the transition is suppressed to voltages above 140 V on alloys with 12 and 26 at.% silicon. The crystalline oxide, nucleated at a depth of ∼40% of the film thickness, is associated with the presence of a precursor of crystalline oxide in the pre-existing air-formed oxide. The modified structure of the air-formed oxide due to increased incorporation of silicon species suppresses the amorphous-to-crystalline transition until the onset of dielectric breakdown. The transport numbers of cations and anions during growth of the anodic oxides are independent of the concentration of silicon species in the inner layer, despite the marked change in the field strength. 相似文献
86.
87.
Shoko Yoshikawa Toshitaka Ota Robert Newnham Ahmed Amin 《Journal of the American Ceramic Society》1990,73(2):263-267
Composite materials composed of randomly dispersed semiconducting ceramic particles in an insulating polymer matrix show a pronounced change in resistivity with pressure. Different amounts of iron oxide (Fe3 O4 ) powder and antimony-doped tin oxide (SnO2 :Sb) powder were dispersed in an epoxy polymer matrix to form pressure-sensitive composites. In each family of materials, an insulator-to-semiconductor transition is observed in agreement with percolation theory. Composites within a certain range of filler content showed substantial piezoresistive effect under both uniaxial and hydrostatic pressure in which sensitivity is controlled by the choice of filler material and the volume fraction. The effect of temperature on the piezoresistance effect was also examined. Piezoresistors made from Fe3 O4 composites showed larger temperature changes than those filled with Sb-doped SnO2 . 相似文献
88.
Ammoxidation of toluene over the perovskites YBa2Cu3O6.1, YBa2Cu2CoO6.7 and YBaCuCoO4.9 was investigated at 400 °C. At low partial pressures of O2 benzonitrile was selectively formed, while CO2 was the main product at high pressures of O2. Systematic differences in activity were observed for the three phases and are related to the crystal contents of Cu and Co. At low O2 pressures, Cu-sites are active for nitrile formation, while Co-sites give CO2. At high O2 pressures, the activity for CO2 of Cu-sites increases more than that of Co-sites due to filling of near-surface oxygen vacancies. 相似文献
89.
电石渣在环氧丙烷生产中的循环利用 总被引:1,自引:0,他引:1
总结了电石渣生产环氧丙烷工艺中的设计与应用。运行情况表明,该工艺具有明显的经济效益和社会效益。 相似文献
90.
Composites consisting of a fine-grained, polycrystalline zinc oxide matrix and <10 vol% coarse, rigid silicon carbide inclusions were prepared by the same mixing procedure and then compacted to produce samples with matrix densities of 0.45 and 0.68 of the theoretical. The samples were sintered under identical temperature profiles in separate experiments that employed either a constant rate of heating of 4°C/min or near isothermal heating at 735°C. The ratio of the densification rate of the composite matrix to the densification rate of the unreinforced zinc oxide was found to be independent of the initial matrix density. This ratio increased significantly with temperature in the constant-heating-rate experiments but was relatively constant in the isothermal experiments. The results indicate that microstructural coarsening may be an important mechanism for explaining the reduced sinterability of polycrystalline matrix composites. 相似文献