Pt-Sn/Al2O3 catalysts:: effect of catalyst preparation and chemisorption methods on H2 and O2 uptake

Pulse and static hydrogen and oxygen chemisorption techniques for determining the platinum dispersion in bimetallic Pt-Sn catalysts were carried out and compared for a monometallic Pt/Al2O3 catalyst and a series of coimpregnated Pt-Sn catalysts containing 1 wt.% of Pt. The pulse chemisorption method gave lower uptakes of hydrogen and oxygen compared to the static volumetric chemisorption method. The differences in hydrogen and oxygen gas uptake behavior can be attributed to the different equilibration times provided by the two chemisorption methods. In the coimpregnated catalyst series, the O/Pt ratio increased with increasing Sn content. The H/Pt ratio, on the other hand, reached the maximum value at 0.1 wt.% Sn. Pulse chemisorption was then used to evaluate how the preparation method affects platinum dispersion and chemisorption behavior. The alumina-supported catalyst series prepared by coimpregnation of Pt and Sn was compared with a series of catalysts prepared by sequential impregnation with tin first, followed by platinum as second component. Coimpregnation of the Al2O3 support with platinum and small amounts of tin facilitates high Pt dispersion, while sequential impregnation of the support with Sn first, followed by Pt, leads to much lower Pt dispersion. (C) 2003 Elsevier B.V. All rights reserved.