Effect of CeO2 and La2O3 promoters on Ni/Al2O3 oxygen carrier performance in chemical looping steam reforming of ethanol for hydrogen production

Abstract

The effects of Ce and/or La on NiO/Al2O3 were studied in chemical looping steam reforming of ethanol. Oxygen carriers (OCs) were prepared by wet impregnation method and characterized by various techniques. The redox test was performed by alternating between fuel feed (FFS) and air feed step (AFS) at 500oC. It was found that Ce- and La-doped improved the OCs’ properties. A suitable amount of Ce- and La-doping helped increase carbon tolerance due to oxygen storage capacity and mobility. The solubility limit was found at 50 mol% La in solid solution. At higher La-doping, La2O3 dispersed on the surface and adsorbed CO2 to form La2O2CO3 during the FFS. From the 1st cycle, N/7LCA displayed the highest H2 yield (3.2 mol/mol ethanol-min). However, after the 5th cycle, N/3LCA exhibited more stability and presented the highest ethanol conversion (88%) and H2 yield (2.5) at 180-min TOS, which decreasing from the 1st cycle 7% and 5%, respectively. Amorphous coke on the OCs decreased with increasing basicity and could be removed at 500oC during AFS, while fibrous coke and La2O2CO3 could not decompose at 500oC. Therefore, after multiple redox cycles, highly La-doped OCs exhibited rather low stability – suggesting that for La-doped OCs, higher regeneration temperature in AFS should be considered while Ni sintering at elevated temperature should be concerned.