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

Abstract

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 NaBH4 reduction; (2) Pt/C with the NaOH-pretreated active carbon, followed by H2 reduction; (3) Pt/C with the support but not-pretreated with NaOH, followed by NaBH4 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 H2 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 H2-reduction for NaBH4-reduction. However, the distances in those catalysts prepared in the present study were longer than those of Pt2+ and Pt4+. The high dispersion of Pt, which is established with the employment of NaBH4-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.