Bifunctional metal-organic frameworks for the hydrogenation of nitrophenol using methanol as the hydrogen source.

This work reports the reduction of 4-nitrophenol to 4-aminophenol using UiO-66(Zr) as a bifunctional photocatalyst and hydrogenation catalyst using methanol as the hydrogen source. In particular, a series of UiO-66(Zr)-X (X: NH2, NO2 and H) and MIL-125(Ti)-NH2 catalysts have been screened as bifunctional catalysts for this process. UiO-66(Zr)-NH2 was found to be the most active material to promote light-assisted nitro hydrogenation under both UV-Vis and simulated sunlight irradiation. The tandem reaction occurs via hydrogen generation from a water/methanol mixture in the first step and, then, reduction of 4-nitrophenol to 4-aminophenol. UiO-66(Zr)-NH2 acts as a truly heterogeneous catalyst and can be reused several times without significant loss of activity, maintaining its crystallinity. This work shows the possibility of using MOFs as solar-driven bifunctional catalysts to promote the hydrogenation of organic compounds using methanol as the hydrogen source.