Liquid-phase chemoselective hydrogenation of 2-ethylanthraquinone over chromium-modified nanosized amorphous Ni-B catalysts

Liquid-phase hydrogenation of 2-ethylanthraquinone to 2-ethylanthrahydroquinone has been investigated over Raney Ni, nanosized amorphous Ni-B, and chromium-modified Ni-B catalysts. It has been found that the amorphous Ni-B and chromium-modified Ni-B catalysts exhibited superior selectivity, whereas the chromium-modified Ni-B catalysts had better activity and selectivity than unmodified Ni-B catalyst. Based on the characterizations, the higher selectivity of the amorphous catalysts is ascribed to the dominant population of the strongly bound hydrogen, which is not reactive for the hydrogenation of the aromatic ring, along with the repulsive interaction between the aromatic ring and the electron-rich Ni due to electron donation from alloying B. The addition of chromium decreased the particle size of the amorphous catalysts, which is beneficial for the improvement of activity. Moreover, surface chromium oxide can function as a Lewis acid, which lowers the πCO* orbital of the reactant, favoring a carbonyl group-bonded configuration. The best selectivity was achieved over the Ni-Cr-B2 catalyst, where the hydrogenation of the aromatic ring was thoroughly blocked before the saturation of the carbonyl groups.