Development of promotors for fast redox reaction of mgmno₃ oxygen carrier material in chemical looping combustion

MgO or gadolinium-doped ceria (GDC, Ce_0.9Gd_0.1O_2-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.