Deactivation of polymer supported palladium catalysts in the hydrogenation of 4-nitrotoluene

The deactivation of palladium catalysts supported on commercially available sulfonated polystyrene-divinylbenzene resins (DOWEX) in the hydrogenation of 4-nitrotoluene was studied. Catalysts were prepared from 4 and 8 mole % crosslinked polymers, with particle size between 0.04 and 0.80 mm and palladium contents ranging from 0.25 to 1 wt.% (dry state). The catalytic tests were carried out in a batch reactor vigorously shaken, at 30-50 °C, and 0.25 and 0.5 MPa. The analysis of the conversion curves showed that three factors are mainly responsible for the relatively high deactivation rates: (i) the concentration of hydrogen in the neighbourhood of palladium crystallites, (ii) temperature, (iii) the nanomorphology of the support. Some practical advice concerning the employment of polymeric hydrogenation catalysts and relevant operational conditions can be achieved from the results presented herein.