Chemical looping gasification of digestate: Investigation on the surface and lattice oxygen of perovskite oxygen carrier

Chemical looping gasification (CLG) offers an attractive route for utilizing digestate. The development of oxygen carrier (OC) is crucial to CLG. In this work, LaFeO3 was employed as the basic OC, and it was doped with different metals at the B site to form LaB0.5Fe0.5O3 (B = Cr, Co, Cu). During the CLG of digestate, LaCu0.5Fe0.5O3 showed the best performance that the gasification efficiency reached 84.71%. OCs were characterized by SEM, XRD, H-2-TPR and EPR, respectively. Results showed that metal doping in the B site increased the surface oxygen content and the mobility of lattice oxygen. It was further confirmed by the DFT calculation. The lowest oxygen vacancy formation energy of LaCu0.5Fe0.5O3 was 5.71 eV, indicating the oxygen in LaCu0.5Fe0.5O3 was easily to migrate. 8-cycles CLG with LaCu0.5Fe0.5O3 was performed to evaluate the stability during the long-term use. With the increase of the cycle, the slight sintering and ash deposition was occurred, which reduced the surface oxygen content and the lattice oxygen migration. Even though, gasification efficiency with LaCu0.5Fe0.5O3 still achieved 72.69% after 8 cycles. This study provides an effective treatment of the digestate, and puts an insight into the oxygen migration of OC.