Additional States of Hydrogen

Additional States of Hydrogen. Temperature programmed desorption (TPD) of H from Pt blacks between 77 and 670 K revealed four peaks (a, P, y, 5) with of 170, 250, 360, and 570 K. A further peak (s, 470 K) has been reported  

Hegedus, G. Besenyei, and F. Nagy, Reaction Kinetics Catalysis Letters, 1976, 5, 73. 

This model is not consistent with recent experimental results. Single crystal data show that all hydrogen adsorbed above 150 K is atomic, and that the i 2. nd states are on geometrically equivalent sites. It is also difficult to see how y and 5 hydrogens can both be on the Pt surface and yet not be in equilibrium. It seems more probable that the y and 5 hydrogens are incorporated in different ways into the Pt, so that H transfer to and from these adsorption sites is a slow activated process. 

Stephen et al have also reported the slow formation of a type of hydrogen which subsequently desorbed at 330 K. The magnitude of the desorption peak was dependent on the time of adsorption at 78 K. About 1 % of a monolayer of extra hydrogen is adsorbed in 10 minutes. 

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