Hydrogen in aromatics. III. Chemisorption of hydrogen in graphite–alkali metal intercalation compounds

Abstract

The hydrogen chemisorption mechanism in the graphite–alkali metal intercalation compounds has been investigated by means of ESR and electrical resistivity under hydrogen atmosphere. In the first stage rubidium compound C8Rb, hydrogen molecules are dissociated into atoms which are stabilized in the interstices of Rb atoms in the gaps of the graphite layers. C8K has a two-stage hydrogen absorption. In the initial stage, the dissociated hydrogen atoms are transiently yielded and then, in the second stage, the formation of hydride ions H− takes place through the charge transfer from C8K to H. C8Cs shows no change in the ESR signal under hydrogen atmosphere. This finding suggests that its catalytic activity for an H–D exchange reaction is due to the surface activity. For the second stage compounds C24K and C24Rb, there exists a one-stage hydrogen absorption process, i.e., absorbed hydrogen directly becomes hydride ion H−. C24Cs shows no change in the ESR signal under hydrogen atmosphere. For the chemisorption activity, the order of the strength is K≳Rb≳Cs in both first and second stage compounds.