THE ROLE OF CARBONACEOUS DEPOSITS AND SUPPORT IMPURITIES IN THE SELECTIVE HYDROGENATION OF ETHYNE

In order to elucidate the role of carbonaceous deposits, the hydrogena tion of ethyne over silica supported Pt and Pd catalysts has been stud ied in a micro-pulse reactor. When a pure silica support (Aerosil) was used, the conversion decreased with an increasing number of ethyne pu lses led over the reactor. Simultaneously, the selectivity towards eth ene increased. When less pure silica (Kieselgel) was used as a support , the opposite effect was observed. These results are explained by ass uming that the carbonaceous deposits are not active, but influence the selectivity of the uncovered metal surface by diminishing the average ensemble size available for the reaction. Impurities in the support c an alter the behaviour of the catalysts.