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• Replicated SCR runs on a Cu-SAPO catalyst show progressive loss of deNO x efficiency. • Non-oxidizing conditions in heating-cooling transients are responsible for deactivation. • High O 2 concentration at high T enables recovery of almost the initial activity. A Cu-SAPO catalyst for NH 3 -SCR applications showed a significant loss of deNO x performance after exposure to oxygen-free conditions. The present work aims at elucidating the causes of the observed progressive deactivation by comparing different experimental procedures for the SCR activity tests. The adoption of an experimental protocol, which avoids the exposure to a non-oxidizing environment, ensured a stable activity of the Cu-SAPO catalyst. Moreover, treatment of the deactivated catalyst with an oxidizing mixture at 550 °C for 5 h enabled to partially recover the deNO x activity. [ABSTRACT FROM AUTHOR]