Studies on the catalysis by the molten metal. XI. An analysis of an anomalous catalytic activity of In-Sn liquid alloy in the dehydrogenation of 2-butanol

Measurements of the rate of 2-butanol dehydrogenation over the In-Sn liquid alloy catalyst have been carried out. In addition, the surface tension of the liquid alloy has been measured at high temperatures and under the atmosphere of 2-butanol vapor. It has been found that the catalytic activity vs catalyst composition curve has a maximum at In/Sn ≒ 1. Furthermore, interesting information about the adsorption of 2-butanol has been obtained from the surface tension data. By assuming a surface unimolecular reaction mechanism, the Hinshelwood-Lindemann's theory has been applied to analyze the experimental data. Thus, it has been shown that the curious relation between the catalytic activity and the catalyst composition is ascribed to the following reasons. (i) The admolecules at In/Sn ≒ 1 have the largest effective internal freedom. (ii) The admolecules with the largest internal freedom must have the smallest chance to be activated. (in) If activated, however, such admolecules are brought to the most strongly energized state. (iv) Hence the admolecules at In/Sn ≒ 1 are able to have the shortest lifetime and decompose with the highest rate.