Layered double hydroxide-derived copper-based oxygen carriers for chemical looping applications: Oxygen release kinetics and impact of loading on long-term performance

Abstract

Chemical looping with oxygen uncoupling, a variant of chemical looping combustion, requires chemically and physically stable oxygen carriers over long-term redox cycling. Copper-based oxygen carriers are characterised by high oxygen release rates but experience sintering at high temperatures. The use of layered double hydroxides (LDHs), prepared via co-precipitation, as oxygen carrier precursors has been shown to effectively limit deactivation of copper-based mixed metal oxides (MMOs) over extended redox cycling. The LDH-derived MMOs have highly dispersed metal oxide within a stable support; the high dispersion of metals is due to the LDH precursor structure. In this work, a fluidised bed reactor (FBR) was used to study the intrinsic kinetics of oxygen release from CuO/MgAl₂O₄ oxygen carriers synthesised via the LDH-MMO design strategy. The long-term performance of MMOs with higher loadings of CuO, calcined from LDHs with higher Cu contents, was also investigated using an FBR. The intrinsic kinetics were determined using a kinetic model incorporating an effectiveness factor. By minimising the effects of intra- and inter-particle mass transfer, the activation energy and the pre-exponential factor of the lower loading MMOs were determined to be 51 ± 3 kJ mol⁻¹ and 0.0567 s⁻¹, respectively. All MMOs showed excellent stability over 100 redox cycles in a thermogravimetric analyser. However, the pH during co-precipitation of the LDHs affected the stability of the MMOs in an FBR. The MMOs calcined from LDHs synthesised at pH 9.5 disintegrated during operation, whilst those produced from LDHs synthesised at pH 11 maintained high conversion and physical integrity over 100 redox cycles. © 2023 The Authors. Greenhouse Gases: Science and Technology published by Society of Chemical Industry and John Wiley & Sons Ltd.