CuO/ZrO2 modified by WO3 oxygen carriers for chemical looping with oxygen uncoupling

The use of mixed metal oxides as oxygen carriers for chemical looping with oxygen uncoupling (CLOU) applications has shown great potential compared to single metal oxide-based oxygen carriers. In this work, the effects of adding WO3 to CuO/ZrO2 oxygen carriers on the oxygen capacity and rate indices for CLOU applications are investigated using nitrogen gas environment. Two synthesis methods were used to prepare the CuO-WO3/ZrO2 oxygen carriers, namely the coimpregnation and sequential impregnation, to evaluate the role of the oxygen carriers' preparation method. The resulting oxygen carriers were thoroughly characterized using XRD, ICP-OES, SEM-EDS and H2-TPR characterization techniques to evaluate the physicochemical properties of the mixed oxide oxygen carriers. The oxygen transport capacity was found to significantly increase for the WO3-modified oxygen carriers compared with the single metal oxide CuO/ZrO2 which was due to the formation of a Cu-W intermediate phases that was found to enhance the redox characteristics of the oxygen carriers. Moreover, the sample synthesized via coimpregnation method displayed higher oxygen release capacity than the sequentially impregnated sample. This was ascribed to the formation a Cu-rich intermediate phase (Cu3WO6) possessing higher Cu/W ratio on the coimpregnated sample compared with a CuWO4-x phase with lower Cu/W ratio and larger crystallite structure formed on the sequentially impregnated oxygen carrier. The mixed metal oxide oxygen carriers also showed a stable redox performance which highlights the potential of WO3 as a modifier to Cu-based oxygen carriers to enhance the oxygen capacity and subsequently decrease the solids inventory. The proposed WO3-based promotors offer significant trait to synthesize Cu-based oxygen carriers with excellent properties for CLOU applications.