“…Based on the reports from Valsamakis et el., [10,11] Masatoe tal., [12,13] and previous work from our group, [14,15] lanthanide oxysulfidesr evealeda similar redox mechanism in the WGS reaction (S 2À $S 6 + )a s CeO 2 (Ce 4 + $Ce 3 + ), but with eightt imes highero xygen storage than CeO 2 .T his categoryo fc atalyst functions well at ultrahigh temperatures (> 700 8C) for the WGS reaction, enabling fast hydrogen production rates as perovskite catalytic systems. [16,17] However,t heir catalytic activities, such as carbon monoxide (CO) conversion and hydrogen (H 2 )s electivity,s till need to be optimized. Therefore, given that occupying the Ln 3 + sites with Na + generates oxygen vacancies and possible lattice change, we hypothesize that sodium dopingm ay result in enhanced catalytic properties of lanthanide oxysulfides towards the WGS reaction, whereas maintaining desirable sulfur tolerance in both sulfur-free and sulfur-rich environments.…”