Wenting Hu

Inhibiting the interaction between FeO and Al 2 O 3 during chemical looping production of hydrogen

Hydrogen of high purity can be produced by chemical looping using iron oxide as an oxygen carrier and making use of the reaction between steam and either iron or FeO. However, this process is viable only if the iron oxide can be cycled between the fully-oxidised and fully-reduced states many times. This can be achieved if the iron oxide is supported on refractory oxides such as alumina. Unfortunately, the interaction between alumina and oxides of iron to form FeAl2O4 hinders the kinetics of the reactions essential to the production of hydrogen, viz. the reduction of Fe(II) to metallic iron by a mixture of CO and CO2 prior to the oxidation by steam. Here, oxygen carriers containing Fe2O3 and Al2O3 were doped with Na2O and, or, MgO, in order to inhibit the formation of FeAl2O4 by forming NaAlO2 or MgAl2O4, respectively. The performance of the modified oxygen carriers for producing hydrogen, i.e. cyclic transitions between Fe2O3 (or Fe3O4) and metallic Fe at 1123 K were investigated. It was found that the interaction between FeO and Al2O3 was successfully mitigated in an oxygen carrier containing Mg, with an Al: Mg ratio of 2, resulting in consistently stable and high capacity for producing hydrogen by chemical looping, whether or not the material was oxidised fully in air in each cycle. However, the oxygen carrier without Mg only remained active when a step to oxidise the sample in air was included in each cycle. Otherwise it progressively deactivated with cycling, showing substantial interaction between Al2O3 and oxides of Fe.

Large scale in silico screening of materials for carbon capture through chemical looping

Chemical looping combustion (CLC) has been proposed as an efficient carbon capture process for power generation. Oxygen stored within a solid metal oxide is used to combust the fuel, either by releasing the oxygen into the gas phase, or by direct contact with the fuel; this oxyfuel combustion produces flue gases which are not diluted by N2. These materials can also be used to perform air-separation to produce a stream of oxygen mixed with CO2, which can subsequently be used in the conventional oxyfuel combustion process to produce sequesterable CO2. The temperature and oxygen partial pressures under which various oxide materials will react in this way are controlled by their thermodynamic equilibria with respect to reduction and oxidation. While many materials have been proposed for use in chemical looping, many suffer from poor kinetics or irreversible capacity loss due to carbonation, and therefore applying large scale in silico screening methods to this process is a promising way to obtain new candidate materials. In this study we report the first such large scale screening of oxide materials for oxyfuel combustion, utilising the Materials Project database of theoretically determined structures and ground state energies. From this screening several promising candidates were selected due to their predicted thermodynamic properties and subjected to initial experimental thermodynamic testing, with SrFeO3−δ emerging as a promising material for use in CLC. SrFeO3−δ was further shown to have excellent cycling stability and resistance to carbonation over the temperatures of operation. This work further advances how in silico screening methods can be implemented as an efficient way to sample a large compositional space in order to find novel functional materials.

The interaction between CuO and Al 2 O 3 and the reactivity of copper aluminates below 1000 °C and their implication on the use of the Cu–Al–O system for oxygen storage and production

The reversible decomposition of CuO into Cu2O and oxygen at high temperature, typically between 850 and 1000 °C, provides a means of separating pure oxygen from air. In such a process, the oxide generally has to be supported on a refractory oxide, e.g. alumina, to maintain its capacity when cycled many times between CuO and Cu2O. One problem is that if the CuO reacts with the alumina to form CuAl2O4, the latter releases oxygen too slowly to be of practical use so that the capacity for oxygen release of such a carrier falls progressively as more aluminate is formed. However, the reported temperatures at which CuAl2O4 forms are inconsistent so far. This work sets out to investigate the interaction between CuO and different aluminas (and precursors), which are commonly used as support materials, at temperatures between 700 and 1000 °C, as well as some chemical properties of the resulting copper aluminates. It was found that the formation of CuAl2O4 occurred at around 700 °C, 800 °C and 950 °C, when amorphous aluminium hydroxide, γ-alumina, and α-alumina were used as the source of alumina support, respectively. The decomposition of CuAl2O4 in an oxygen-lean environment can lead to the formation of α-alumina as well as γ-alumina, depending on the partial pressure of oxygen. Given that the α-form does not react with CuO around 900 °C, the typical operating temperature for the CuO/Cu2O couple, this observation can be used to partially regenerate CuO from CuAl2O4, for oxygen storage and production at this temperature by decomposing the spinel in a controlled atmosphere to form only α-alumina. However, during the decomposition of CuAl2O4, delafossite CuAlO2 is also formed, limiting the amount of Cu that could be recovered as CuO in a single process cycle.

Data supporting "The use of strontium ferrite in chemical looping systems"

A R T I C L E I N F O

Supporting Data for 'Large scale in silico screening of materials for carbon capture through chemical looping'

This data was generated as part of the EPSRC grant EP/K030132/1. It contains: 1. MaterialsProject-ScreenedOxidationReactions.xlsx: A spreadsheet with all the screened oxidation reaction obtained from the Materials Project database (www.materialsproject.org). Description of each column: a. Composition - Formula of reactant material b. O2 chemical potential - Chemical potential under which the reaction takes place. c. dE_EV - Change in energy of the reaction (calculated by DFT at 0 K) d. O2 capacity - gravimetric O2 capacity of the reaction, based on the stoichiometry e. Temp - temperature at which the equilbrium constant was calculated (here chosen to be 298.15 K, room temperature) f. Kp at T - calculated equilibrium constant g-j. T_oxidation at p_XXX - Temperature at which the oxidation reaction takes place under different partial pressures of O2 k. Reaction - Screened oxidation reaction (this is separated across several columns). 2. XRD.zip - folder containing raw x-ray diffraction data for the compounds presented in the paper. 3. SI-TGA.zip - folder containing raw TGA data for Figure S1 4. TGA.zip - folder containing raw TGA data (ForPaper.xlsx) and Matlab file (ForPaper.m) to produce figures.

Theoretical and experimental screening methods for functional materials design

Matthew Dunstan1, Cindy Lau2, Can Kocer1, Wenting Hu3, John Dennis4, Andrew Morris5, Stuart Scott2, Clare Grey1 1Department Of Chemistry, University Of Cambridge, Cambridge, United Kingdom, 2Department of Engineering, University of Cambridge, Cambridge, United Kingdom, 3School of Chemical Engineering and Advanced Materials, Newcastle University, Newcastle, United Kingdom, 4Department of Chemical Engineering and Biotechnology, University of Cambridge, Cambridge, United Kingdom, 5Department of Physics, University of Cambridge, Cambridge, United Kingdom E-mail: mtd33@cam.ac.uk

Research data supporting "The interaction between CuO and Al2O3 and the reactivity of copper aluminates below 1000°C and their implication on the use of the Cu-Al-O system for oxygen storage and production"

The data set contain the original research data presented in the paper corresponding to the relevant figures and table shown in the article and the accompanying supplementary information.