A Mössbauer Spectroscopy Study of Platinum-Tin Reforming Catalysts

Mössbauer spectroscopy measurements were made to observe alloy formation and interaction of tin with the alumina support in two Pt-Sn/alumina catalysts. The catalysts were rich in tin with an atomic ratio of Pt : Sn = 0.7 : 1. One was prepared by coimpregnation and the other by a sequential impregnation technique. Spectra of samples reduced in a stream of 10% H2 in argon gave evidence of a solid solution of tin in platinum with a composition approaching Pt3Sn for most reduction conditions. A large fraction of the tin, 70-80%, interacted strongly with the alumina and did not alloy with the platinum. Two stannous species were identified in the nonalloyed fraction. One was produced by strong interaction with the alumina and the other was a surface ion. Steaming produced large stable crystallites including the intermetallic, Pt3Sn, and SnO2. The spectroscopic data were supported by TPR measurements. The results show that platinum and some of the tin reduce between 400 and 700°K with formation of the alloy. The remaining tin reduces to the stannous state between 800 and 850°K.