Distribution of platinum particles in the bimodal micropore system of activated carbon

Platinum (Pt)/activated-carbon catalysts were prepared and characterized by pore-size distribution (PSD), propane-sorption dynamics, and activity of cyclohexane dehydrogenation to benzene. The batch-type frequency-response (FR) spectroscopic technique was applied to determine the mass-transport rate of propane sorption. Two parallel sorption processes of different time constants were distinguished, suggesting that adsorption proceeds in smaller and larger micropores that are not interconnected. Increasing Pt loading affected the propane mobility, but increased the dehydrogenation activity only up to ca. 1 wt-% of Pt content. It was concluded that clusters of metallic Pt-atoms are located preferentially at the narrowest pores. Blocking these micropores, the Pt reduces the carbon surface available for sorption; also, a significant fraction of the metal becomes inaccessible for the reactant.