MgO or gadolinium-doped ceria (GDC, Ce0.9Gd0.1O2-δ) was added as a promoter to improve the oxygen transfer kinetics of MgMnO3 oxygen carrier material for chemical looping combustion. Neither MgO nor GDC reacted with MgMnO3, even at the high temperature of 1100 oC. The average oxygen transfer capacities of MgMnO3, 5 wt% MgO-MgMnO3, and 5 wt% GDC-MgMnO3 were 8.74, 8.35, and 8.13 wt%, respectively. Although the addition of MgO or GDC decreased the oxygen transfer capacity, no further degradation was observed during their use in 5 redox cycles. The addition of GDC significantly improved the conversion rate for the reduction reaction of MgMnO3 compared to the use of MgO due to an increase in the surface adsorption process of CH4 via oxygen vacancies formed on the surface of GDC. On the other hand, the conversion rates for the oxidation reaction followed the order 5 wt% GDC-MgMnO3 > 5 wt% MgO-MgMnO3 >> MgMnO3 due to morphological change. MgO or GDC particles suppressed the grain growth of the reduced MgMnO3 (i.e., (Mg,Mn)O) and increased the specific surface area, thereby increasing the number of active reaction sites.

Keywords: Chemical looping combustion, Oxygen carrier material, Oxygen transfer capacity, Conversion rate, Promoter