Bimetallic RhIn/ZIF-8 for the Catalyic Chemoselective Hydrogenation of Nitrostyrene: Exploration of Natural Selectivity of Hydrogen Sources and Enhancing Intrinsic Selectivity

Chemoselective hydrogenation of nitrostyrene to aminostyrene still faces the trouble of low selectivity and poor activity. The bimetallic catalysts, which adjust the activity of noble metal nanoparticles through the doping of non-noble metals, are promising for selectively catalytic transfer hydrogenation (CTH). For another aspect, the hydrogen source also plays a vital role in selective CTH. Based on this, we prepared activity-inhibited bimetallic RhIn/ZIF-8 catalyst to study the catalytic performance towards different hydrogen sources (N2H4·H2O, NaBH4, NH3·BH3 and H2) and to explore the natural selectivity of these hydrogen sources. We found that the hydrazine hydrate was the most selective H-donor for the nitro group, while the H2 had the highest natural selectivity to olefins. The H2 produced from hydrazine hydrate is responsible for the formation of completely reduced products. The potential reduction by the intermediate imine did not occur to CC double bonds, this indicates controlling the decomposition of N2H4 will enhance the selectivity of nitroarenes. Based on this, the reaction system with the catalyst bimetallic RhIn/ZIF-8 and N2H4·H2O as the hydrogen source is established, which can fully reduce many nitrostyrenes with >98% selectivity to corresponding aminostyrenes.