Controlled preparation and characterization of plurimetallic Pt-Sn and Pt-Ir-Sn/Al2O3 reforming catalysts

The preparation of bimetallic 0.6 wt.% Pt-x wt.% Sn/Al2O3 and trimetallic 0.5 wt.% Pt-0.1 wt.% Ir-x wt.% Sn/Al2O3 and 0.3 v/t.% Pt-0.3 wt.% Ir-x wt.% Sn/Al2O3 catalysts (0 < x < 0.4) by surface redox reaction between hydrogen activated on a parent platinum or platinum-iridium catalyst and tin chloride (SnCl4) dissolved in hydrochloric medium ("catalytic reduction" method) was investigated. Elemental analysis of catalysts indicated that tin can be deposited by surface redox reaction, this reaction competing with the adsorption of the tin precursor on the alumina support. The deposition on the metal by redox reaction being more rapid than the one on the support by exchange, the reaction time was limited to 15 min. Moreover, the addition of citric acid in the acidic medium allowed to decrease both the tin deposit on the Support and the chloride content of the catalysts. The characterization of tin modified catalysts by temperature programmed reduction and by activity measurements for cyclohexane dehydrogenation showed that a large amount of tin is deposited on or close to the active metallic phase. (C) 2004 Elsevier B.V. All rights reserved.