Chemical looping combustion (CLC) is an energy conversion technology capable of producing energy from fossil fuels while capturing CO₂. The technology is based on using a metal oxide as an oxygen carrier (OC), which undergoes cyclic oxidation and reduction operations. The performance of OCs can be enhanced by the support on which they are deposited.
In this work, we investigate and compare the synergetic effect of two different supports of TiO₂ and MgO on the NiO oxygen carrier reduction reaction with H₂ by periodic density functional theory (DFT) calculations. Not only the synergetic effect of support but also the oxygen vacancy-support interactions are considered in this study.
Reactivity of OC is affected by the addition of support, as the surface charge distribution of the OC that undergoes the reduction reaction is controlled by charge transfer between metal oxide and support. Oxygen vacancy formation energy is also affected by the addition of support and charge transfer at the interface. This charge transfer is proportional to the difference between the electronegativity (the Fermi level relative position) of the support and metal oxide. A more electron enriched or deficient reaction site can change the energetics of the reaction. In this work, a more by adding TiO₂ support, the positively charged surface of NiO enhances the reduction reaction as a result of higher electron donation by H₂ to the surface. This behavior is also observed by the addition of MgO support to NiO. However, the different nature of these supports and the difference in charge transfer at the interface causes different changes in the energetics of the reaction.
An in-depth understanding of the effect of support is carried out by analyzing the Bader charge and DOS analysis of the system, which can help us for the selection of appropriate support.

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