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The effect of moderate sintering of the platinum particles of a precoked Pt/SiO2 catalyst on the transformation of n-PB was investigated under reforming conditions (773 K, 5 bar, and H2/HC = 5). The results showed that the larger the platinum particles, the greater the formation of cyclic compounds. Furthermore, a concentration balance between the ethylbenzene and the cyclic compounds was revealed, suggesting a common reactive adsorbate for both reaction products. According to a previously proposed reactive adsorbate for ethylbenzene and the results of studies of Pt/SiO2 and PtSn/SiO2 catalysts, a reactive adsorbate was proposed for the formation of the cyclic compounds. This latter reactive adsorbate, which results from the reactive adsorbate leading to ethylbenzene, is consistent with either a decrease in the size of the Pt ensembles or an increase in the electron density of the platinum particles of the Pt/SiO2 catalyst sample with the smaller particles after coke deposition. It is still uncertain as to whether the concentration balance phenomenon is due to a geometric ensemble effect, a change in the electronic density of the platinum clusters, or both. The studies with a tin-promoted catalyst were discussed in relation to this new finding and a detailed reaction network for the transformation of n-PB over metallic sites is proposed. |
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