Local structure around platinum in Pt/C catalysts employed for liquid-phase dehydrogenation of decalin in the liquid-film state under reactive distillation conditions

摘要

The dehydrogenation of decalin to naphthalene in the liquid-film state has been investigated on Pt/C catalysts under reactive distillation conditions at 483 K.The catalysts were prepared from the following three procedures:(1) Pt/C with active carbon pretreated with aqueous NaOH solution,followed by NaBH_4 reduction;(2) Pt/C with the NaOH-pretreated active carbon,followed by H_2 reduction;(3) Pt/C with the support but not-pretreated with NaOH,followed by NaBH_4 reduction.The highest activity for evolution of hydrogen from the dehydrogenation of decalin to naphthalene was observed on Pt/C prepared using the procedure (1).The employment of H_2 reduction and the support not-pretreated with NaOH afforded lower activities.Extended X-ray absorption fine structure (XAFS) analyses revealed that the nature of platinum was strongly influenced by both the NaOH-treatment and the reduction procedures.The nearest-neighbor distance of Pt-Pt in the active catalyst was evidently shorter than those in metallic platinum and in the catalyst prepared from the support not-pretreated with the NaOH solution,while it was longer than the catalyst prepared from the employment of H_2-reduction for NaBH_4-reduction.However,the distances in those catalysts prepared in the present study were longer than those of Pt~(2+) and Pt~(4+).The high dispersion of Pt,which is established with the employment of NaBH_4-reduction and the support pretreated with NaOH,affords a more covalent nature for the platinum species,resulting in the highest activities for the dehydrogenation of decalin to naphthalene.