Efficient Metal-Organic Framework-Derived Cu-Zr Oxygen Carriers with an Enhanced Reduction Reaction Rate for Chemical Looping Air Separation

As a key to realize the chemical looping air separation (CLAS) process, CuO is a good oxygen carrier candidate because of its high oxygen transport capacity and excellent thermodynamic characteristics. However, it is hampered by easy deactivation during redox cycles. In this work, a Cu-Zr oxygen carrier is developed via a metal-organic framework (MOF) self-templated method to realize high redox reactivity and favorable thermal stability for the CLAS process. The physicochemistry property and reduction kinetics are investigated through isothermal redox cycles, material characterizations, and reduction kinetic modeling. Compared to the coprecipitated oxygen carrier (Copr.), the MOF-derived oxygen carrier (MOFD) obtains a 35% faster average reaction rate at the temperature interval of 800-900 degrees C, especially a 60% reduction rate increase at 850 degrees C. This enhanced reaction rate is mainly ascribed to the lower intrinsic activation energy (126.3 kJ center dot mol(-1) for MOF-D vs 157.3 kJ center dot mol(-1) for Copr.) rather than the amount of active oxygen species. The oxygen-releasing mechanisms for the MOF-derived and coprecipitated oxygen carriers follow the nucleation and nuclei growth model with a transition of one-dimensional growth to two-dimensional nucleation at two temperature ranges (800-825 and 850-900 degrees C). This study offers a new route to develop an efficient oxygen carrier for the CLAS process.