Synergy of Rh Nanoparticles With Fe3O4 for Efficient Selective Catalytic Transfer Hydrogenation of Nitrostyrenes Using Stoichiometric Hydrazine Hydrate

Hydrazine hydrate as a hydrogen source has a good effect on nitro reduction, but overuse has environmental toxicity and is prone to over-hydrogenation, resulting in low selectivity. Herein, we report a magnetically separable Rh/Fe 3 O 4 (1.26 wt%) catalyst containing an optimal Rh content that can completely convert 3-nitrostyrene to 3-vinylaniline (> 99% selectivity) using a stoichiometric molar ratio of hydrazine hydrate (-NO 2 :N 2 H 4 ·H 2 O = 1:1.5). This is due to the synergy between Rh and Fe 3 O 4 and the natural selectivity of N 2 H 4 ·H 2 O for nitro. The synergy can reduce the activation energy of the reaction (36.6 kJ/mol), increasing the reduction rate of nitro group and avoiding the combination of active hydrogen species (H*) to H 2 as well as the hydrogenation of N 2 H 4 to NH 3 . Moreover, the active H* produced by N 2 H 4 ·H 2 O is different from that produced by H 2 , and excess dose of N 2 H 4 will inevitably yield H 2 thus decline the selectivity.