Abstract
Pd‐active carbon‐type catalysts are used in a wide variety of processes, typical examples of which are liquid‐phase hydrogenation reactions. In the case of these catalysts, a loss of their catalytic activity is observed. The aim of the present work was to assess the possibility of regenerating spent Pd/AC catalysts using supercritical fluid extraction. The following Pd/AC catalyst samples were investigated and compared: a commercial 10 wt % Pd catalyst (Aldrich) (denoted by CC), a spent catalyst (SC), SC subjected to supercritical fluid–CO~2~ extraction (SC/SFE/C), SC subjected to supercritical fluid–CO~2~–ethanol extraction (SC/SFE/C‐Et), and SC subjected to supercritical fluid–ethane–propane extraction (SC/SFE/E‐P). The last three catalysts were additionally subjected to heating in a hydrogen atmosphere at 410 K for 3 h. These were denoted by SC/SFE/C/H, SC/SFE/C‐Et/H, and SC/SFE/E‐P/H, respectively. The spent Pd/AC catalyst (SC) consists of mixed CC samples used in the reduction with hydrogen of various organic compounds. The catalysts CC, SC/SFE/C, SC/SFE/C/H, SC/SFE/C‐Et/H, and SC/SFE/E‐P/H were tested in the reduction of octanoylbenzene with hydrogen. The activity of the catalysts was estimated by measuring the reaction time and also the amount of hydrogen used in relation to the theoretical quantity required for the reaction. XPS and XRD methods were used to evaluate the changes occurring in the form of the palladium present on the Pd/AC catalyst surface during the regeneration processes. It was found that supercritical fluid‐CO~2~ extraction followed by heating in a hydrogen atmosphere is the most effective method for regenerating that catalyst. The results of our investigations indicate that regeneration of a spent Pd/AC catalyst, irrespective of the reaction in which it has been used, should be based on the complete removal of byproducts, the purification of the catalyst surface, and the restoration of the original form of the palladium. The procedure proposed in this paper, i.e. SFE (CO~2~) and heating in H~2~, fulfils both the conditions mentioned above. © 2007 American Institute of Chemical Engineers Environ Prog, 2007