8The redox properties and oxygen buffering capacity of reducible oxides, such as ceria, make 9 them interesting support materials for oxygen carriers in chemical looping combustion (CLC), an 10 emerging clean combustion technology. However, the effectiveness of reducible oxides for redox 11 applications depends crucially on oxygen mobility in the oxide lattice. In the present work, we 12 demonstrate that addition of an aliovalent dopant (La) strongly enhances oxygen mobility in 13 ceria, resulting in multiple performance benefits. A series of La-doped ceria (La x Ce 1-x O 2-x/2 , 0 < 14 x < 0.3) were investigated as supports for low-cost Fe-based oxygen carrier materials. 15 Combining carrier synthesis and characterization with reactive tests, we demonstrate that La 16 doping of ceria not only results in a drastic improvements in carrier reactivity and oxygen 17 carrying capacity, but also strongly improved carrier stability during redox cycling. This is 18 consistent with the creation of oxygen defects, which stabilize the supported Fe particles and 19 facilitate oxygen transport in the ceria lattice. A balance between enhancement of oxygen 20 mobility and lowered reducibility upon formation of a lanthana phase results in a strongly 21 nonlinear dependence of carrier reactivity on the dopant concentration and gives rise to an 22 Corresponding Author: Götz Veser (gveser@pitt.edu) © 2016. This manuscript version is made available under the Elsevier user license http://www.elsevier.com/open-access/userlicense/1.0/ 2 optimum at low dopant concentrations. Overall, the results suggest that doping of reducible 23 supports constitutes a highly attractive, effective, and low-cost way to strongly enhance the 24 performance of oxygen carriers in chemical looping applications. 25 26 1. Introduction: 28Increasing supply of energy is imperative for continued growth of modern society, particularly in 29 the so-called developing world. The International Energy Agency (IEA) predicts that global 30 primary energy demand will increase by almost 20% over the next 15 years alone. Although the 31 share of fossil fuels is predicted to decrease slightly from 82% now to 76% by 2035, energy-32 related CO 2 emissions are expected to rise by 20% over the same time-frame 1, 2 . As the source of 33 two-thirds of the global greenhouse-gas emissions, technological advances in the energy sector 34 will be pivotal in abating CO 2 emissions. Given our dependence on fossil fuels, alternative 35 technology solutions for clean combustion of fossil fuels with simultaneous CO 2 capture should 36 hence have high priority in our energy R&D landscape. 37Chemical Looping Combustion (CLC) has emerged over the past decade as a particularly 38 promising technology in this context, offering a highly efficient route for clean combustion of 39 fossil fuels with inherent CO 2 capture 3-5 . In CLC, an oxygen carrier (typically a metal oxide) is 40 contacted with fuel in a first reactor (fuel reactor), undergoing reduction while providing the 41 necessary oxy...
A novel methodology combining mathematical optimization with DFT calculations is developed to determine highly cohesive transition metal nanoclusters.
Determining the energetically most favorable structure of nanoparticles is a fundamentally important task towards understanding their stability. In the case of bimetallic nanoclusters, their vast configurational space makes it especially...
We propose a novel computational framework for the robust optimization of highly nonlinear, non‐convex models that possess uncertainty in their parameter data. The proposed method is a generalization of the robust cutting‐set algorithm that can handle models containing irremovable equality constraints, as is often the case with models in the process systems engineering domain. Additionally, we accommodate general forms of decision rules to facilitate recourse in second‐stage (control) variables. In particular, we compare and contrast the use of various types of decision rules, including quadratic ones, which we show in certain examples to be able to decrease the overall price of robustness. Our proposed approach is demonstrated on three process flow sheet models, including a relatively complex model for amine‐based CO2 capture. We thus verify that the generalization of the robust cutting‐set algorithm allows for the facile identification of robust feasible designs for process systems of practical relevance.
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