- 标题
- 摘要
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Europium-Catalyzed Aerobic Oxidation of Alcohols to Aldehydes/Ketones and Photoluminescence Tracking
摘要： Europium is a lanthanide rare-earth metal and is known as a key element in luminophore development. Since europium has two relatively stable oxidation states, Eu2+ and Eu3+, which is exceptional among the various lanthanide elements, we have developed a europium-catalyzed aerobic oxidation with external oxidants utilizing the redox cycle of Eu2+/Eu3+. The reaction was performed under mild conditions with a wide substrate scope. The photoluminescence spectra clearly demonstrate the oxidation state changes that occur during the presented europium-catalyzed aerobic oxidation.
关键词： europium,oxidation,redox cycle,photoluminescence,homogeneous catalysis
更新于2025-09-23 15:22:29
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High efficiency solar chemical-looping methane reforming with ceria in a fixed-bed reactor
摘要： High ef?ciency solar chemical-looping methane reforming is demonstrated in a prototype reactor operated in a high-?ux solar simulator. The reactor includes six tube assemblies, which each comprise a ?xed-bed of ceria particles and a gas-phase heat recuperator. The cycle was accomplished by alternating the ?ow to one tube assembly between CH4 and CO2. In the initial series of experiments, temperature, CH4 concentration, reduction ?ow rate, and cycle duration were varied to minimize carbon accumulation and maximize ef?ciency. In the second set of tests, the reactor was operated at optimized conditions for ten cycles at 1228 and 1274 K. Higher temperature favors better performance. At 1274 K, CH4 conversion is 0.36, H2 selectivity is 0.90, CO selectivity is 0.82, CO2 conversion is 0.69, and the energetic upgrade factor is 1.10. Heat recovery effectiveness is over 95%. Solar-to-fuel ef?ciency is 7% and the thermal ef?ciency is 25%. Projected solar-to-fuel and thermal ef?ciencies are 31 and 67% for the full-scale reactor and 56 and 85% for a commercial reactor with lower thermal losses. The demonstrated ef?ciencies are the highest reported to-date for this process. The projected scaled-up ef?ciencies suggest solar chemical-looping methane reforming could be a competitive approach for production of solar fuels.
关键词： Reforming,Redox cycle,Solar thermochemical,Chemical-looping,Metal oxide,Ceria
更新于2025-09-23 15:22:29
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Experimental framework for evaluation of the thermodynamic and kinetic parameters of metal-oxides for solar thermochemical fuel production
摘要： The two-step metal oxide redox cycle is a promising and thermodynamically attractive means of solar fuel production. In this work, we describe the development of a high-temperature tubular reactor in which the fundamental thermodynamic and kinetic behaviour of thermochemical materials can be readily assessed. This reactor system is capable of operating at temperatures up to 1873 K, total pressures ranging from vacuum to ambient, and oxygen partial pressures (pO2) as low as 10-29 atm. Compared to off-the-shelf systems like thermogravimetric analyzers (TGA) or indirect conductivity-based measurement systems, this system has three inherent benefits: (1) the flexibility to control the sample morphology (e.g. powder, packed bed, reticulated porous ceramic, or pellet), (2) the potential for a well-developed and characterized flow, and (3) the ability to readily customize the system on demand (e.g. easy integration with a steam generator to control and operate at very low pO2). The reactor system and experimental methods were validated by performing isothermal relaxation experiments with undoped ceria, wherein the sample environment was rapidly altered by stepwise changes in the delivered H2O vapor concentration, and comparing measured oxygen nonstoichiometries with accepted data available in the literature. Data was measured at temperatures from 1173-1473 K and pO2 from 4.54×10-18-1.02×10-9 atm. The measured equilibrium data displayed strong agreement with the literature and the expected trends were preserved. Kinetic data was extracted by first transforming reactant concentrations measured downstream of the reaction zone using a tanks-in-series mixing model to account for gas dispersion. Next, a mechanistic kinetic model distinguishing surface and bulk species concentrations was fit to the data to extract pertinent thermodynamic and kinetic parameters. The model assumed a two-step reaction mechanism mediated by the formation of an intermediate hydroxyl species on the surface. Activation energies and defect formation enthalpies and entropies for the forward and reverse reactions were found to be in good agreement with previous modelling efforts, providing further validation of the use of this system to explore thermodynamic and kinetic behaviour of emerging thermochemical materials.
关键词： thermodynamic and kinetic parameters,undoped ceria,solar fuel production,metal oxide redox cycle,high-temperature tubular reactor
更新于2025-09-09 09:28:46