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The effect of carburization of palladium catalysts on the hydrogenation of acetylene-ethylene mixtures

Borodziński A.

Polish Journal of Chemistry

1998

Vol. 72, nr 11

2455-2462

During the hydrogenation of acetylene-ethylene mixtures on palladium catalysts, the rate of acetylene disappearance and the concentration of carbon dissolved in the bulk palladium increase similarly for samples metal crystallite size<25nm. Such a positive correlation supports the hypothesis that carburization of palladium is responsible for the increase of the rate of acetylene disappearance during againg of the catalyst. The maximum concentration of carbon in palladium at the steady-state depends on the temperature of the reaction and on the crystallite size. This concentration increases with carburization temperature and decreases with the increase of Pd crystallite size. The presence of supersaturated solution of carbon in Pd at 50 degree C is possible, due to a diffusion-hindered frozen state in the bulk. The catalytic properties of such a sample match the behavior of partially carburized Pd catalyst at steady-state conditions. This result strongly suggests that, in both cases, concentrations of surface carbon are similar.