Hydrogen-bearing phases relationships

As has been seen, only on the transition metals can cathodic hydrogenation involving chemisorbed H atoms occur. Thus results obtained using cathode metals such as Hg or Pb, even if they numerically resembled gas-phase rates, would not be expected to bear any theoretical relationship to them. Only a small minority of cathodic hydrogenations on the transition metals have been reported, and of these almost none include the mechanistic and kinetic information needed to make a valid rate comparison. 

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