ABSTRACT
Abstract Carbon supported powdered palladium catalysts have been widely used in the chemical industry. In addition to activity and selectivity of those catalysts, the recovery rate of the incorporated precious metal has a major impact on the economic performance of the catalyst. In this study, the effects of catalyst age, oxidation state of the incorporated metal and temperature treatment on the palladium leaching resistance as well as on activity and dispersion of carbon supported palladium catalysts were investigated. Introduction Palladium-based precious metal powder catalysts are used for a wide variety of industrial hydrogenation reactions. In general, these catalysts are refined after use to capture the value of the incorporated metal. Due to attrition and metal leaching during the hydrogenation reaction, a significant part of the precious metal can be lost. Even though the majority of the leached metal can be recovered using metal scavengers like Degussa’s Deloxan®, the metal loss can have an important influence on the overall economics of the catalytic process. Aim of catalyst research is thus to minimize the amount of metal losses. As a continuation of a previous study, this work investigates the influence of the catalyst age, degree of reduction, wetness of the catalyst and type of metal deposition (egg shell and uniform) on the leaching resistance as well as on hydrogenation activity and dispersion of powdered carbon supported palladium catalysts. (1) The leaching resistance of the catalysts was investigated by stirring the catalysts in a solution of ammonium chloride, which is known to be a model system to mimic the precious metal leaching in hydrogenation reactions. (2) The resulting mixtures were filtered and the mother liquor was analyzed for Pd by inductively coupled plasma (ICP). Another part of our investigation deals with the effect of heat treatment on the leaching behavior of palladium on activated carbon catalysts. Heat treatment is a known technique to increase the performance of catalysts. (3) Therefore, standard carbon supported palladium catalysts were exposed to different temperatures ranging from 100 to 400 °C under nitrogen. The catalysts were characterized by metal leaching, hydrogenation activity and CO-chemisorption.
