Development of promotors for fast redox reaction of MgMnO3 oxygen carrier material in chemical looping combustion

Abstract

MgO or gadolinium-doped ceria (GDC, Ce0.9Gd0.1O2-δ) was added as a promoter to improve the oxygen transfer kinetics ofMgMnO3 oxygen carrier material for chemical looping combustion. Neither MgO nor GDC reacted with MgMnO3, even atthe 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 oxygentransfer capacity, no further degradation was observed during their use in 5 redox cycles. The addition of GDC significantlyimproved the conversion rate for the reduction reaction of MgMnO3 compared to the use of MgO due to an increase in thesurface adsorption process of CH4 via oxygen vacancies formed on the surface of GDC. On the other hand, the conversionrates for the oxidation reaction followed the order 5 wt% GDC-MgMnO3 > 5 wt% MgO-MgMnO3 >> MgMnO3 due tomorphological change. MgO or GDC particles suppressed the grain growth of the reduced MgMnO3 (i.e., (Mg,Mn)O) andincreased the specific surface area, thereby increasing the number of active reaction sites.