Catalysis of Organic..

476 Palladium LeachingResults and DiscussionThe influence of the catalyst age on the leaching resistance of precious metal powdercatalysts was investigated. Eggshell and uniform, reduced and unreduced, dry andwet type palladium on activated carbon catalysts were prepared and characterized bytheir hydrogenation activity, metal dispersion and palladium leaching. The testedcatalysts show a relatively high leaching in the first few days after preparation. Thisvalue drops remarkably in the first weeks after preparation. The hydrogenationactivity and palladium dispersion did not change significantly during the same timeperiod. The properties of the investigated catalysts of this study as well as theirhydrogenation activities and palladium dispersions are summarized in table 1 andtable 2.Table 1. Properties of investigated catalystsERD ERW END ENW URD URW UND UNWeggshell eggshell eggshell eggshell uniform uniform uniform uniformreduced reduced nonreducednonreducedreduced reduced nonreducednonreduceddry wet dry wet dry wet dry wetThe reduced catalysts show a significantly higher metal leaching compared to thecorresponding non-reduced catalysts. The amount of Pd detected when leaching thecatalysts four weeks after preparation was between 100 and 150 ppm for theinvestigated reduced catalysts and between 20 and 40 ppm for the non-reducedcatalysts. No significant differences between the egg-shell and the uniform typecatalysts were observed in this test.metal leached [ppm]A160.00140.00120.00100.0080.0060.0040.0020.000.00ERD ERW END ENW URD URW UND UNWdecrease in metal leaching [%]B60.0040.0020. 000. 00-20.00ERD ERW END ENW URD URW UND UNWFigure 1A, B. Leaching results one month after catalyst preparation and relativedecrease in Pd leaching compared to the leaching of a fresh catalystSimilar trends were found for the palladium leaching values when leaching freshcatalysts. However, the overall amount of palladium leached is higher in this case.The results of the leaching tests performed one day after the catalyst preparationshow values between 140 and 240 ppm for the reduced and of 30 to 60 ppm for thenon-reduced catalysts. A comparison of the decrease of metal leaching over timeshows different aging effects for the dry catalysts compared to the wet catalysts of