An attempt has been made to stabilize the high temperature P-NiMoO4 phase which is catalytically more selective in oxidative dehydrogenation of alkanes at room temperature through irradiation by gamma-rays. Different samples of stoichiomertic alpha-NiMoO4 were subjected to different doses of gamma-irradiation in the range of 50-500 kGy. The effect of gamma-irradiation on the alpha- to beta-NiMoO4 transition temperature was studied using differential thermal analysis (DTA) technique with controlled rate of heating and cooling. The formation of beta-NiMoO4 phase was investigated by means of XRD and FT-IR techniques. The catalytic performance of the resulting catalyst samples in the oxidative dehydrogenation of cyclohexane at 500,C was investigated. The DTA investigation revealed that gamma-irradiation effectively lowers the temperature of the a 0 transition in NiMoO4 but did not affect the temperature of beta-to-alpha return transition. A new peak characteristic of beta-phase was detected at 2 theta = 26.3 degrees in the XRD patterns of gamma-irradiated samples. FT-IR analysis also confirmed the formation of beta-NiMoO4 where a new band characteristic of P-phase was observed at 879 cm(-1) in the spectra of these samples. In view of the XRD results, the observed change in the alpha- to beta-NiMoO4 transition temperature was attributed to the fact that radiation induced a strain in the alpha-NiMoO4 crystals. On the other hand, catalytic activity results indicated that gamma-irradiated nickel molybdate catalysts showed a high selectivity towards cyclohexene at isoconversion (5%) in comparison with that of unirradiated parent alpha-NiMoO4. (C) 2008 Elsevier B.V. All rights reserved.