Abstract
The sulfur deactivation of 6% Pt/SiO2 (Europt-1) and 0.3% Pt/Al2O3 (Europt-3) catalysts for carbon monoxide, ethene, and ethyne adsorption and ethyne hydrogenation has been investigated, using sulfur-labeled hydrogen sulfide, 35S-H2S, and 14C-radiotracer of the corresponding adsorbate at 293-323K. Adsorption of 35S-H2S occurs in two stages. On Europt-1, it showed a non-linear primary region followed by a linear secondary region, while on Europt-3, it showed a linear primary region followed by a plateau region. A small fraction (ca. 5%) of the adsorbed sulfur species can be removed by evacuation. It is suggested that at high sulfur coverages, H2S < 0.5, these catalysts’ surfaces undergo some reconstruction.
It was observed that the effect of sulfur poisoning on the selectivity for ethene formation was beneficial for the alumina-supported catalysts. whilst detrimental to the silica-supported catalysts. Furthermore, sulphur promotes carbon monoxide and ethene adsorption on the Al2O3 acidic sites. In addition, it appears that the poisoning behavior of sulphur on the hydrocarbons adsorption and ethyne hydrogenation on these catalysts is simply due to a hydrocarbon site-blocking effect.
Evidence has been obtained to support our previous proposals that, on steady state catalysts and under the influence of hydrocarbon adsorption and ethyne hydrogenation reactions, a surface reconstruction process occurs and ethyne hydrogenation takes place in the secondary adsorption region. Collectively, the results indicate that Europt-1 and Europt-3 catalysts under clean and sulphur poisoning conditions exhibited a high thermodynamic selectivity but low mechanistic selectivity towards ethyne hydrogenation reaction.