Chemical looping oxygen transfer properties of Cu-doped lanthanum oxysulphate

Abstract

La2O2SO4 was investigated as a candidate high capacity oxygen carrier for Chemical Looping processes based on the occurrence of the redox cycle of sulphur from S+6 to S−2 leading to the reversible formation of the corresponding lanthanum oxysulphide (La2O2S). The effect of the addition of copper (1% wt.) on the redox properties and thermal stability of La2O2SO4 during high temperature reduction/oxidation cycles was also studied.Temperature Programmed Reduction and Oxidation experiments were carried out cyclically at temperatures up to 1027 °C respectively with 2% H2/Ar and 0.5% O2/He mixtures. Fresh and used carriers were characterized by ICP-MS, XRD, BET and SEM analysis. Regardless of copper doping the material reversibly changed from La2O2SO4 to La2O2S and vice versa restoring each time the corresponding crystalline structure with a complete oxygen recovery. Copper addition decreased the peak temperature for both reduction and oxidation, likely due to the enhanced oxygen mobility in the La-oxysulphate/oxysulphide structures.For comparison purposes, CaSO4 tested under identical conditions dramatically lost its Oxygen Storage Capacity across each redox cycle due to irreversible formation of CaO instead of CaS.