Praseodymium doped ceria, a material of interest for electrochemical flue gas purification, was investigated with in situ X-ray Absorption Near Edge Structure spectroscopy between room temperature and 500°C in air and diluted nitrogen(II) oxide (NO/Ar) (1% NO in Ar). For temperatures above 400°C in NO/Ar a reversible energy shift towards lower energy was observed for the Pr edge, indicating a reduction of Pr4+ to Pr3+, while the edge position of Ce remained unchanged. The concentration of Pr3+ ions was quantified and obtained results are in good agreement with predictions from defect thermodynamic modeling.