Redox Kinetics Study of Fuel Reduced Ceria for Chemical-Looping Water Splitting

Chemical-looping water splitting is a novel and promising technology for hydrogen production with CO₂ separation. Its efficiency and performance depend critically on the reduction and oxidation (redox) properties of the oxygen carriers (OC). Ceria is recognized as one of the most promising OC candidates, because of its fast chemistry, high ionic diffusivity, and large oxygen storage capacity. The fundamental surface redox pathways, including the complex interactions of mobile ions and electrons between the bulk and the surface, along with the adsorbates and electrostatic fields, remain yet unresolved. This work presents a detailed redox kinetics study with emphasis on the surface ion-incorporation kinetics pathway, using time-resolved and systematic measurements in the temperature range 600–1000 °C. By using fine ceria nanopowder, we observe an order-of-magnitude higher hydrogen production rate compared to the state-of-the-art thermochemical or reactive chemical-looping water splitting studies. We show that the reduction is the rate-limiting step, and it determines the total amount of hydrogen produced in the following oxidation step. The redox kinetics is modeled using a two-step surface chemistry (an H2O adsorption/dissociation step and a charge-transfer step), coupled with the bulk-to-surface transport equilibrium. Kinetics and equilibrium parameters are extracted with excellent agreement with measurements. The model reveals that the surface defects are abundant during redox conditions, and charge transfer is the rate-determining step for H₂ production. The results establish a baseline for developing new materials and provide guidance for the design and the practical application of water splitting technology (e.g., the design of OC characteristics, the choice of the operating temperatures, and periods for redox steps, etc.). The method, combining well-controlled experiment and detailed kinetics modeling, enables a new and thorough approach for examining the defect thermodynamics in the bulk and at the surface, as well as redox reaction kinetics for alternative materials for water splitting

Web Service Discovery in a Semantically Extended UDDI Registry: the Case of FUSION

Service-oriented computing is being adopted at an unprecedented rate, making the effectiveness of automated service discovery an increasingly important challenge. UDDI has emerged as a de facto industry standard and fundamental building block within SOA infrastructures. Nevertheless, conventional UDDI registries lack means to provide unambiguous, semantically rich representations of Web service capabilities, and the logic inference power required for facilitating automated service discovery. To overcome this important limitation, a number of approaches have been proposed towards augmenting Web service discovery with semantics. This paper discusses the benefits of semantically extending Web service descriptions and UDDI registries, and presents an overview of the approach put forward in project FUSION, towards semantically-enhanced publication and discovery of services based on SAWSDL

Enhancing co-production of H[subscript 2] and Syngas via Water Splitting and POM on Surface-Modified Oxygen Permeable Membranes

In this article, we report a detailed study on co-production of H2 and syngas on La[subscript 0.9]Ca[subsvript 0.1]FeO[subscript 3−[delta] (LCF-91) membranes via water splitting and partial oxidation of methane, respectively. A permeation model shows that the surface reaction on the sweep side is the rate limiting step for this process on a 0.9 mm-thick dense membrane at 990°C. Hence, sweep side surface modifications such as adding a porous layer and nickel catalysts were applied; the hydrogen production rate from water thermolysis is enhanced by two orders of magnitude to 0.37 μmol/cm2•s compared with the results on the unmodified membrane. At the sweep side exit, syngas (H[subscript 2]/CO = 2) is produced and negligible solid carbon is found. Yet near the membrane surface on the sweep side, methane can decompose into solid carbon and hydrogen at the surface, or it may be oxidized into CO and CO[subscript 2], depending on the oxygen permeation flux. © 2016 American Institute of Chemical Engineers AIChE J, 62: 4427–4435, 2016Shell Oil CompanyKing Abdullah University of Science and Technolog

Design and Development of Superconducting Parallel-Bar Deflecting/Crabbing Cavities

The superconducting parallel-bar cavity is a deflecting/crabbing cavity with attractive properties that is being considered for a number of applications. We present the designs of a 499 MHz deflecting cavity developed for the Jefferson Lab 12 GeV Upgrade and a 400 MHz crabbing cavity for the LHC High Luminosity Upgrade. Prototypes of these two cavities are now under development and fabrication

Kinetic Effects of Non-Equilibrium Plasma-Assisted Methane Oxidation on Diffusion Flame Extinction Limits

The kinetic effects of plasma assisted fuel oxidization on the extinction of partially premixed methane flames was studied at 60 Torr by blending 2% CH 4 into the oxidizer stream. The experiments showed that the non-equilibrium plasma can dramatically accelerate the fuel oxidization at low temperature. The prompt fuel oxidization resulted in fast chemical heat release and extended the extinction limits significantly. The O production and the products of plasma assisted fuel oxidation were measured, respectively, by using twophoton absorption laser-induced fluorescence (TALIF) method, Fourier Transform Infrared (FTIR) spectrometer, and Gas Chromatography (GC). The product concentrations were used to validate the plasma assisted combustion kinetic model. The comparisons showed the kinetic model over-predicted the CO, H 2 O and H 2 concentrations and under-predicted CO 2 concentration. The O concentration prediction from the kinetic model intersected with experimental results. A path flux analysis showed that O was majorly generated by the discharge and dictated the plasma assisted fuel oxidization. So the deviation between experiments and simulations was caused by the inaccurate prediction of O. This is due to missing reaction pathways, such as those involving excited species (e.g. excited O) and the validity of radical consumption reactions with hydrocarbon species at low temperature range

Toward enhanced hydrogen generation from water using oxygen permeating LCF membranes

Hydrogen production from water thermolysis can be enhanced by the use of perovskite-type mixed ionic and electronic conducting (MIEC) membranes, through which oxygen permeation is driven by a chemical potential gradient. In this work, water thermolysis experiments were performed using 0.9 mm thick La[subscript 0.9]Ca[subscript 0.1]FeO[subscript 3−δ] (LCF-91) perovskite membranes at 990 °C in a lab-scale button-cell reactor. We examined the effects of the operating conditions such as the gas species concentrations and flow rates on the feed and sweep sides on the water thermolysis rate and oxygen flux. A single step reaction mechanism is proposed for surface reactions, and three-resistance permeation models are derived. Results show that water thermolysis is facilitated by the LCF-91 membrane especially when a fuel is added to the sweep gas. Increasing the gas flow rate and water concentration on the feed side or the hydrogen concentration on the sweep side enhances the hydrogen production rate. In this work, hydrogen is used as the fuel by construction, so that a single-step surface reaction mechanism can be developed and water thermolysis rate parameters can be derived. Both surface reaction rate parameters for oxygen incorporation/dissociation and hydrogen–oxygen reactions are fitted at 990 °C. We compare the oxygen fluxes in water thermolysis and air separation experiments, and identify different limiting steps in the processes involving various oxygen sources and sweep gases for this 0.9 mm thick LCF-91 membrane. In the air feed-inert sweep case, the bulk diffusion and sweep side surface reaction are the two limiting steps. In the water feed-inert sweep case, surface reaction on the feed side dominates the oxygen permeation process. Yet in the water feed-fuel sweep case, surface reactions on both the feed and sweep sides are rate determining when hydrogen concentration in the sweep side is in the range of 1–5 vol%. Furthermore, long term studies show that the surface morphology changes and silica impurities have little impact on the oxygen flux for either water thermolysis or air separation.Shell Oil CompanyKing Abdullah University of Science and Technolog