PLATINUM-TIN CATALYSTS SUPPORTED ON SILICA HIGHLY SELECTIVE FOR N-HEXANE DEHYDROGENATION

Citation
J. Llorca et al., PLATINUM-TIN CATALYSTS SUPPORTED ON SILICA HIGHLY SELECTIVE FOR N-HEXANE DEHYDROGENATION, Journal of catalysis, 166(1), 1997, pp. 44-52
Citations number
24
Categorie Soggetti
Chemistry Physical
Journal title
ISSN journal
00219517
Volume
166
Issue
1
Year of publication
1997
Pages
44 - 52
Database
ISI
SICI code
0021-9517(1997)166:1<44:PCSOSH>2.0.ZU;2-3
Abstract
Silica-supported Pt-Sn catalysts were prepared by two-step impregnatio n from [PtCl2(PPh(3))(2)] and SnCl2 solutions of appropriate concentra tions to yield Pt/Sn atomic ratios ranging from 0.2 to 5.0. In these s ystems, the presence of true Pt-Sn alloys was confirmed by X-ray diffr action, transmission electron microscopy, energy dispersive X-ray anal ysis and electron nanodiffraction. Pt and PtSn ahoy phases were found on catalysts with Pt/Sn > 1, PtSn alloy alone on the catalyst with Pt/ Sn = 1 and PtSn and PtSn2 alloys, together with Sn in the catalysts wi th Pt/Sn < 1. All these catalysts were tested in the skeletal reaction s of n-hexane at 753 K and atmospheric pressure. The selectivity of Pt changed significantly when alloyed with tin. For Sn-rich compositions a segregation of tin toward the catalyst surface was shown by photoel ectron spectroscopy, and high hydrogenolysis selectivity and fast deac tivation were observed. In contrast, Pt-rich catalysts, in which a wel l defined PtSn alloy was observed, were much more stable and exhibited high selectivity to dehydrogenation reaction while maintaining low co nversions to benzene and hydrogenolysis products. This selectivity pat tern can be interpreted in terms of a change in adsorption properties due to differences in the number of adjacent Pt atoms required for the various reaction pathways. (C) 1997 Academic Press.