Abstract

Chemical Looping represents a promising new technology for achieving cheap and efficient separation of CO2 in energy generation processes. The chemical looping technique is based on the redox cycle of an oxygen carrier, usually a transition metal oxide, which reacts endother- mically with a fuel, according to: (2n m)MyOx CnH2m → (2n m)MyOx−1 mH2O + nCO2. (1) The reduced metal oxide is then transferred to the air reactor where it is oxidised by the highly exothermic reaction: MyOx−1 + 1O2 → MyOx, (2) 2 where n, m, x and y are stoichiometric coefficients. Spin-polarized Density Functional Theory (DFT) calculations were performed for geometry optimization of ceria in Vienna Ab-initio Simulation Package (VASP) using the range sepa- rated hybrid functional HSE06 and GGA +U (PBE+U), where both methods are appropriately applied.[1] PBE +U was shown to accurately describe the electron localisation of the system while only calculating qualitatively correct energy differences, while the hybrid functionals (HSE) were considered a better choice to calculate both the lattice parameters and electronic properties (band gaps and density of states (DOS)) of such materials. The Fe-doped and Zn-doped cerium oxides were studied to increase the oxygen vacancy con- centration and concomitant oxide ion conductivity in CeO2 by Ce+4/Ce+3 substitution with metal ions of a lower valence.[2],[3] The effect of oxygen vacancies and different dopants on ceria will be discussed.

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