The oxidative dehydrogenation of n-hexane over Ni–Mo–O catalysts

Abstract

The effect of chemical composition on nickel–molybdenum catalysts in the oxidative dehydrogenation of n-hexane was studied. The catalysts consisted of the following phases: nickel oxide, molybdenum trioxide, nickel molybdate (α-NiMoO 4 and β-NiMoO 4) and a solid solution of nickel in a lattice of nickel molybdate. Characterization of the catalysts was carried out using ICP-OES, BET, XRD, FTIR, SEM, TPR and XPS techniques. The effect of phase composition of the catalysts on their catalytic activity and selectivity to the products obtained in the temperature range 300–500 °C was also studied. The most selective catalyst for the synthesis of hexenes was the pure β-NiMoO 4, which gave 25% selectivity to 1-hexene and 10% selectivity to 2-hexenes and 3-hexenes at 9% conversion. The pure phases NiO and MoO 3, although active in hexane ODH, showed poor selectivity to hexenes, particularly to 1-hexene at comparable conversions suggesting that they are not responsible for the catalytic activity of the NiO–MoO 3 system. The pure β-phase was more selective towards the hexenes than the α-phase with the difference in the molybdenum coordination believed to be the reason for the different activities and selectivities of the two modifications of NiMoO 4. The α-phase with MoO 3 was more active, suggesting that a synergetic effect plays an important role in modifying catalytic activity.