Nanoscience and Technology

Biography

Biography: Hayder Alalwan

Abstract

Transition metal oxide nanoparticles were used as oxygen carriers  chemical looping combustion (CLC), a promising indirect combustion process that facilitates carbon capture. The focus of the investigation was to identify the reduction mechanism of the transition metal oxides during CLC using a continuous flow through system and spectroscopic, microscopic, and thermo gravimetric analysis. The comparison of the reactivity of copper (CuO), iron (α-Fe2O3) and cobalt (Co3O4) oxides with methane (CH₄) in CLC reveals a link between the solid-state reduction mechanism of CLC oxygen carriers and their size-dependent reactivity toward CH₄. The results show that the reactivity of CuO and Co3O4 are independent of the particle size, with reduction following the nucleation and nuclei growth (NNG) model, whereas α-Fe2O3 shows increased reactivity with decreasing particle size and reduction follows the unreacted shrinking core (USC) model. Supported by density functional theory (DFT) calculations comparing relative energies of formation for surface and bulk oxygen defects, we propose a conceptual framework for the size-dependence of metal oxide oxygen carriers for CLC. For oxygen carriers that reduce via the NNG model, where reduction initiates within the particle core, there will be no size dependence. For reduction via the USC model, where reduction initiates on the particle surface, reactivity will increase for smaller particles. These findings can guide development of metal oxide oxygen carriers for CLC by establishing trends in size-dependent behavior.