The influence of addition of sliver ions on the redox properties and catalytic performance of molybdenum-phosphate catalyst in oxidative dehydrogenation (ODH) of propane has been investigated. MoO3 and AgMoO2PO4 have been detected in Ag-doped Mo-P-O catalysts. The redox properties have been characterized by H-2-temperature-programmed reduction (TPR), electronic paramagnetic resonance (EPR) and X-ray photoelectron spectroscopy (XPS). The catalytic performance of MoO3, Ag2O, AgMoO2PO4 and Ag-doped Mo-P-O catalysts has also been examined. The incorporation of Ag improved the number of Mo5+ species and the reducibility of the catalysts. The Ag-doped catalysts favor activity and selectivity in ODH of propane higher than the undoped catalyst. The best catalyst was obtained with Ag/Mo ratio of 0.3 and MoO3/AgMoO2PO4 ratio of 1.1. The influence of promoter Ag' on redox properties and catalytic performance is due to forming redox couple "Ag-0 + Mo6+ double left right arrow Ag+ + Mo5+" and the synergetic effect originating from "coherent interface" between MoO3 and AgMoO2PO4. (C) 2003 Elsevier B.V. All rights reserved.