Hydrogen production via chemical looping steam reforming of ethanol by Ni-based oxygen carriers supported on CeO2 and La2O3 promoted Al2O3

Abstract

This work studies the effects of Ce4+ and/or La3+ on NiO/Al2O3 oxygen carrier (OC) on chemical looping steam reforming of ethanol for hydrogen production - alternating between fuel feed step (FFS) and air feed step (AFS). Suitable amount of Ce- and La-doping increases OC carbon tolerance. The solubility limit is found at 50 mol% La in solid solution. At higher La-doping, La2O3 disperses on the surface and adsorbs CO2 forming La2O2CO3 during FFS. From the 1st cycle, 12.5 wt%Ni/7 wt%La2O3-3wt%CeO2–Al2O3 (N/7LCA) displays the highest averaged H2 yield (3.2 mol/mol ethanol) with 87% ethanol conversion. However, after the 5th cycle, 12.5 wt%Ni/3 wt%La2O3-7wt%CeO2–Al2O3 (N/3LCA) exhibits more stability and presents the highest ethanol conversion (88%) and H2 yield (2.7 mol/mol ethanol). Amorphous coke on the OCs decreases with increasing La3+ content and can be removed at 500 °C during AFS; nevertheless, fibrous coke and La2O2CO3 cannot be eliminated. Therefore, after multiple redox cycles, highly La-doped OCs exhibits rather low stability.