Properties of Pt/C and Pd/C catalysts prepared by reduction with hydrogen of adsorbed metal chlorides: Influence of pore structure of the support

Abstract A number of catalysts have been prepared by adsorption of H 2 PdCl 4 and H 2 PtCl 6 on activated carbons of different origin followed by drying and reduction in flowing hydrogen. They were characterised by CO chemisorption and by liquid-phase hydrogenation of cyclohexene, cyclooctene and nitrobenzene. A decisive influence of the pore structure of the support on the catalyst properties has been found. By a proper choice of the preparation conditions, it proved possible to obtain a sufficiently high dispersion of the supported metal on any one of the activated carbons used. However, catalytic activity per mass of metal reached a maximum in the range of intermediate metal dispersion, with the limit being dependent on the support used. This is attributed to deposition of metal particles of high dispersion in narrow pores of the supports, which renders part of the metal surface inaccessible to the organic substrates. Such a blocking effect proved especially significant for Pt catalysts on the activated carbons with the smallest micropores.