Characterization, kinetics and stability studies of NiO and CuO supported by Al2O3, ZrO2, CeO2 and their combinations in chemical looping combustion

Abstract

This study investigates the synthesized NiO- and CuO-based carriers supported by Al2O3, CeO2, ZrO2 and their combinations in chemical looping combustion (CLC). The oxygen carriers were tested in a thermogravimetric analyzer (TGA), where the results showed that the oxygen capacity increased using mixed support oxides in both NiO-based and CuO-based samples. The reducibility of CeO2 played a role in the increase of oxygen capacity and in the case of NiO-based samples, the reduction of NiAl2O4 phase as promoted by the formation of CeAlO3 played a role, as well. For NiO-based samples, a significant increase of carbon deposition occurred for mixed support oxides (Al2O3-ZrO2, Al2O3-CeO2 and Al2O3-ZrO2-CeO2) at 750 °C in comparison with the use of one support while the differences were negligible at 950 °C. To examine the structure and properties of the oxygen carriers, they were characterized by XRD, SEM/EDX and XPS. Comparison of fresh and used samples revealed sintering of active-sites particles on the surface of supports as evident of EDX mapping images and the decrease in active-site to support ratio in the XPS analysis. NiO/Al2O3-ZrO2-CeO2 was found to be a potential oxygen carrier for further CLC studies and scaleup.