MoO₃ Catalysed Hydrogenation of Nitrobenzene to Aniline at Near Room Temperature

MoO₃ with orthorhombic structure (α-MoO₃) was evaluated for its catalytic performance in the hydrazine-assisted transfer hydrogenation of nitrobenzene to aniline at near room temperature. The conversion of nitrobenzene, ca. 88.6% was obtained after 4 h reaction with >99% of selectivity to aniline. The activation energy from the Arrhenius plot was ca. 120.6 kJ/mol. In this system, hydrazine (N₂H₄) did not only act as a hydrogen donor but also as a reducing agent to generate an active catalytic phase as supported by the existence of an induction period at the early stages of the reaction. XRD and XPS characterisations of the hydrazine treated catalyst revealed the phase transformation from α-MoO₃ to (NH₄)_0.23H_0.08MoO₃ containing Mo⁵⁺ species, a possible adsorption site for hydrazine decomposition to produce active hydrogen species for the transfer hydrogenation of nitrobenzene. Based on the Hammett plot, an anionic intermediate was indicated to be involved in the rate-determining step.