Understanding CuO-support interaction in Cu-based oxygen carriers at a microcosmic level

Abstract

Oxygen carrier (OC) which is able to release and absorb O2 repeatedly is the key issue of chemical looping with oxygen uncoupling (CLOU). Active component (typically, metal oxide) is usually supported by inert component to enhance the thermal stability and mechanical strength of OC particle. A clear understanding on the interactions of different phases (active material and support material) in OC particles could help rationalize the design of high-performance OC. In this work, periodical density functional theory (DFT) calculation, thermo-mechanical analysis (TMA), and isothermal decomposition experiments were jointly conducted to gain insight into the effects of different supports (TiO2, ZrO2, CuAl2O4 and MgAl2O4) on the Cu-based OC performance in terms of sintering resistance and decomposition reactivity. CuO nanocluster was positioned on support slab with periodical boundary condition to simulate the impregnation-derived OCs. First, the adsorption energies of CuO nanocluster on four supports, which can be used to assess the sintering resistance characteristics of the supports, were calculated via DFT. It was found that ZrO2 is most conducive to sintering resistance of OC particles, followed by CuAl2O4, MgAl2O4, and TiO2 (in that order). Then, the energy barriers of oxygen release process were examined to evaluate the effect of support on the OC decomposition reactivity. Results showed that the desorption of O2 molecule formed on the OC surface is the rate-determining step for all supported CuO. The O2 desorption energy barriers increases in the order of CuO/CuAl2O4<CuO/ZrO2<CuO/MgAl2O4<CuO/TiO2, showing CuAl2O4 as support is in best favor of CuO decomposition among four supports. The effects of support on OC performance were explained by the strong interactions between CuO nanocluster and support slab, resulting in significant electron redistribution and microstructure changes of CuO nanocluster. The microcosmic mechanism understandings to sintering resistance and decomposition reactivity were well supported by TMA and isothermal decomposition experiments, respectively.