An organometallic approach for tin promotion Pt/y-Al203 alkane dehydrogenation catalysts

GERARDO F. SANTORI; MONICA L. CASELLA; GUILLERMO J. SIRI; OSMAR A. FERRETTI; JOSE LUIS GARCIA FIERRO

STUDIES IN SURFACE SCIENCE AND CATALYSIS

ELSEVIER SCIENCE BV

Año: 2000 vol. 130 p. 3897 - 3902

0039-3037

Pt catalysts supported on alumina and promoted by tin, were investigated. The dehydrogenation of isobutane was selected as test reaction. Tin was added using the Surface Organometallic Chemistry on Metals techniques and the atomic ratio Sn/Pt ranged from 0 to 1.6. Catalysts were characterized by FTIR of chemisorbed CO and NH3 on reduced samples.The band of CO chemisorbed on Pt at 2074 cm -~ shifts to higher wavenumbers upon Sn incorporation indicating an electronic interaction Sn-Pt which weakens the Pt-CO bond. The modification introduced by the addition of tin in the distribution of Lewis and Brrnsted acid sites, was put in evidence by FTIR spectra of adsorbed NH 3, being Brtinsted sites partially poisoned. The oxidation state of the metals after reduction was determined by XPS: Platinum is present as Pt ~ and tin is present both as Sn ~ and Sn n+. The fraction of metallic tin decreases as the amount of promoter increases. The addition of Sn increases substantially the stability of the catalysts. Selectivities towards cracking and isomerization reactions diminish and dehydrogenation selectivity increases as the tin loading increases.