The hydrothermal stability of CuAPSO-34 microporous silicoaluminophosphates with chabasite structures has been investigated and compared to that of a copper-exchanged ZSM-5 zeolite by a combined XRD, FTIR, and catalytic study. CuAPSO-34 showed a higher hydrothermal structural stability (steaming 80 h at 600 degreesC), as found by XRD. Spectroscopic FTIR investigation of adsorbed CO revealed that upon this steaming procedure the concentration of monovalent copper ions in CuAPSO-34 was not significantly affected, whereas, even after a less severe steaming (60 h at 550 degreesC), these species dramatically decreased in CuZSM-5, and extraframework Al3+ ions were simultaneously formed. Consequently, the high activity in N2O decomposition shown by fresh CuZSM-5 was essentially lost after steaming, while CuAPSO-34 exhibited a significantly milder deactivation. (C) 2003 Elsevier Science (USA). All rights reserved.