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

A number of catalysts have been prepared by adsorption of H2PdCl4 and H2PtC l6 on activated carbons of different origin followed by drying and reductio n in flowing hydrogen. They were characterised by CO chemisorption and by l iquid-phase hydrogenation of cyclohexene, cyclooctene and nitrobenzene. A d ecisive influence of the pore structure of the support on the catalyst prop erties 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 dis persion, with the limit being dependent on the support used. This is attrib uted 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 fo r Pt catalysts on the activated carbons with the smallest micropores. (C) 2 000 Elsevier Science B.V. All rights reserved.