FTIR study of bimetallic Pt-Sn/Al2O3 catalysts

Abstract

A series of Pt-Sn/Al2O3 catalysts supported on Degussa nonporous alumina were characterized by infrared spectroscopy of adsorbed CO. The nominal platinum loading was kept constant in the catalysts at 1 wt% and the nominal amount of tin was varied from 0 to 5 wt%. At room temperature it was found that there was a general trend for the linearly adsorbed CO band to shift to lower frequencies with increasing amounts of tin in the catalyst, except for one of the catalysts (1.0 Pt-1.0 Sn/Al2O3) where a particle size effect seemed to be dominant. The amount of bridge-bonded CO species was very small and became undetectable in the case of large tin loadings (1 and 5 wt% Sn). Thermal desorption infrared spectroscopy was used to determine the vibration frequency of the isolated CO molecule and hence observe if there were any indications of electronic interactions between tin and platinum. For the monometallic 1.0 Pt/Al2O3 sample the singleton vibration frequency was 2041 cm-1. For all the Pt-Sn bimetallic samples it was found that the singleton vibration frequency lay within the range 2041 +/- 6 cm-1. This suggests that the electronic effect of Sn on Pt in our Pt-Sn/Al2O3 catalysts is not very large.