Sintering of platinum-black in hydrogen: Morphology and catalytic activity

Pt-black (Pt-473 and Pt-633) reduced in aqueous solution with HCHO was sintered at 473 and 633 K in hydrogen. Electron micrographs show a considerable sintering, especially at 633 K. High-resolution EM indicates the presence of agglomerates of rounded crystals; lattice fringes are also seen. Samples sintered at different temperatures show identical catalytic activity in ring opening and aromatization of alkylcyclopentanes; their activity was also similar in bond-shift isomerization of heptane isomers. On the other hand, aromatization, hydrogenolysis, and C5-cyclic isomerization were more rapid on Pt-473, while C5-cyclization was more rapid on Pt-633. These effects are discussed in terms of various active sites for these skeletal reactions and their abundance on two samples which have different morphology, hence different hydrogen retention ability; also the chemical state of their carbon impurity may be different