ABSTRACT
In this study precious metal powder catalysts were prepared on wood-based carbons that underwent two different activation processes: 1) with phosphoric acid and 2) with steam. Reduced and unreduced catalysts were prepared on these carbons using chloride and nitrate precious metal (Pt, Pd) salts. Mother liquors and washing solutions collected during the catalyst preparations were analyzed by inductively coupled plasma (ICP) to determine the amount of soluble precious metal (PM). Temperature-programmed desorption (TPD) was used to characterize the functional groups on the carbon surface. The results presented suggest that palladium chloride is only strongly adsorbed on the steam-activated carbon, but not on the phosphoric acid-activated carbon. For two unreduced catalysts leaching was observed with palladium chloride on the phosphoric acid-activated carbon support (0.277wt.% Pd loss), whereas, little or no leaching was observed on the steam-activated carbon (0.005lwt.% Pd loss). To a lesser extent the same effect was also observed with reduced-type catalysts. Changing the precious metal precursor from palladium chloride to palladium nitrate or platinum ,chloride reduced the PM loss during the catalyst preparation. Pretreatment of the phosphoric acid-activated carbon by water washing or thermal treatment in inert gas minimized the PM loss problem. A specific type of C-0 functional group on the carbon surface is suspected to be responsible for PM loss during the catalyst preparation.
