Deactivation of palladium catalyst supported on functionalized resins in the reduction of aromatic nitrocompounds

We report on the liquid phase hydrogenation (1 M solution in methanol) of 4-nitrotoluene and 4-nitrophenol over Pd catalysts supported on anionic resins (sulphonated 4% crosslinked poly {styrene-divinylbenzene}, 5 meq./g ion exchange capacity, particles size 0.16–0.32 mm) at room temperature and pressure 0.25–1 MPa. The initial reaction rate in the hydrogenation of 4-nitrotoluene was more than ten times higher than that of 4-nitrophenol. Recycled catalysts were strongly deactivated: whereas in the hydrogenation of 4-nitrotoluene the extent of deactivation was proportional to leaching of palladium, it was not so in the case of 4-nitrophenol. Hence, the structure of the palladium crystallites surface is likely to play an important role. The stability of palladium catalysts was improved by addition of cobalt, which not only suppresses the leaching of palladium, but in proper amount also enhances the rate of hydrogenation of 4-nitrotoluene.