YBa2Cu3O7 was prepared by means of the citric acid complexing method. The catalytic performances of N2O decomposition over fresh and 250 degreesC-reduced YBa2Cu3O7 have been evaluated. Techniques such as XRD, TGA, XPS, EPR, TPD, pulsing, in-situ DRIFT, and FT-Raman were employed to investigate the natures of active sites and to identify the possible reaction intermediates. A catalytic reaction mechanism has been proposed. The N2O decomposition activity over the fresh YBa2Cu3O7 is lower than that over the reduced one. Being reduced at 250 degreesC in H-2, YBa2Cu3O7 transformed from an orthorhombic to a tetragonal structure in which there were Cu2+, Cu2+ and oxygen vacancies. The redox action amongst Cu2+delta double left right arrow Cu2+ double left right arrow Cu2-delta over the fresh sample and that amongst Cu1+delta double left right arrow Cu+ double left right arrow Cu1-delta over the reduced sample are essential for N2O decomposition. Species such as N2O22-, O-2(-), O-2(2-), NO3-, NO2-, and [NO2O2](2-) are generated during N2O decomposition. The key step is the decomposition of N2O22-. (C) 2001 Elsevier Science B.V. All rights reserved.