Molecular Dynamics Simulation of the Microscopic Sintering Process of CuO Nanograins Inside an Oxygen Carrier Particle

CuO-based materials as oxygen carrier (OC) always exhibit a weak sintering resistance at high temperature, which leads to a significant decrease of reactivity in chemical looping processes. Inert component is usually added to enhance the thermal stability and increase the specific surface area of OC particles. Detailed knowledge on the sintering mechanism of CuO nanograins within the bulk of OC particles and the interactions between active component and inert support materials is thus of considerable importance. In this study, molecular dynamics (MD) method was conducted to explore the fundamental understanding of CuO sintering mechanism and the effects of different support materials (TiO2, ZrO2, and SiO2) on the sintering resistance of supported CuO nanograins. The sintering simulations of pure CuO nanograins show that CuO particle with smaller diameter or at higher temperature tends to be more amorphous. With respect to the sintering of two unsupported nanograins, it can be concluded that the neck growth during sintering is the joint effect of surface diffusion and grain boundary diffusion. Among these three composite OCs (CuO supported by TiO2, ZrO2, or SiO2), CuO/ZrO2 shows a better sintering resistance. The enlarged discrepancy on the surface area loss between different supported CuO nanograins with the rising of temperature emphasizes the importance of rational selection of support materials at high temperature.