DEACTIVATION OF POLYMER-SUPPORTED PALLADIUM CATALYSTS IN THE HYDROGENATION OF 4-NITROTOLUENE

The deactivation of palladium catalysts supported on commercially avai lable sulfonated polystyrene-divinylbenzene resins (DOWEX) in the hydr ogenation of 4-nitrotoluene was studied. Catalysts were prepared from 4 and 8 mole % crosslinked polymers, with particle size between 0.04 a nd 0.80 mm and palladium contents ranging from 0.25 to 1 wt.% (dry sta te). The catalytic tests were carried out in a batch reactor vigorousl y shaken, at 30-50 degrees C, and 0.25 and 0.5 MPa. The analysis of th e conversion curves showed that three factors are mainly responsible f or the relatively high deactivation rates: (i) the concentration of hy drogen in the neighbourhood of palladium crystallites, (ii) temperatur e, (iii) the nanomorphology of the support. Some practical advice conc erning the employment of polymeric hydrogenation catalysts and relevan t operational conditions can be achieved from the results presented he rein.