Abstract
An attempt was carried out to improve the catalytic performance of alpha-NiMoO4 in partial oxidative dehydrogenation of alkanes. Different catalyst samples were reduced by hydride anion, H-, using CaH2 in the temperature range 100-450 degrees C. The catalytic performance of the resulting catalyst samples in the oxidative dehydrogenation of cyclohexane at different temperatures and at atmospheric pressure was investigated. The phase composition of iriolybdate and reduction products was analyzed by XRD. Reduction of alpha-NiMoO4 with CaH2 at temperatures above 200 degrees C yielded reduction products consisting of crystalline Ni and MoO2, intermetallic compounds between Ni and Mo, and incompletely reduced alpha-NiMoO4, whereas reduction of alpha-NiMoO4 with H-2 is not possible under the same conditions applied. Nickel molybdate catalyst, reduced 14 with CaH2 at 450 degrees C, showed a high selectivity toward cyclohexene at isoconversion (5%), in comparison with that of parent alpha-NiMoO4 and that of catalyst reduced with hydrogen. In view of the XRD results, the significant high selectivity of this catalyst toward cyclohexene was attributed to the fact that reduction by 14 CaH2 modified the crystal structure "cell dimensions" of the incompletely reduced alpha-NiMoO4. On the other hand, a synergetic effect between the new phases founded in this catalyst sample after reduction and the incompletely reduced alpha-NiMoO4 was proposed.