Hydrogen spillover in Pt-Sn catalysts supported on activated carbon cloth

The effect of the tin content and the reduction temperature on the ability of bimetallic platinum-tin catalysts supported on activated carbon cloth (ACC) to retain hydrogen after the reduction treatments has been analysed by temperature-programmed desorption of hydrogen (H₂-TPD). A series of Sn/ACC samples with different tin contents has been prepared by impregnation of ACC with a solution of tin (II) oxalate in diluted HNO₃ and subsequent heat-treatment at 623 K under flowing helium. Platinum (1wt.%) was then introduced by impregnation of the Sn/ACC samples with aqueous solutions of H₂PtCl₆. Catalysts have been characterised by temperature-programmed reduction under diluted hydrogen and X-Ray Photoelectron Spectroscopy (XPS). The extent of hydrogen spillover from the metallic particles to the support has been determined by H₂-TPD, the products being analysed by on-line mass spectrometry. The presence of tin oxide provides anchoring sites for hydrogen atoms spilt-over from platinum, although the ability of the latter to dissociate H₂ molecules seems to be influenced by the presence of tin, both in an oxidised state after reduction at low temperature (523 K) and in the metallic state (possibility of alloy formation) after reduction at higher temperatures (623 and 723 K).