INDUCED SURFACE HETEROGENEITY AS AN AUTOCATALYTIC WAY TO PROMOTE ACID-BASE HETEROGENEOUS REACTIONS

Alkaline hydrides MH are insoluble in all known solvents. Dispersed in strictly anhydrous solvents, KH has an extraordinary behavior with re spect to Bronsted acids HA: it reacts with difficulty with strong acid s, but reacts readily with weak acids. The reason for this behavior is ascribed to the fact that the reaction K+H(s-) + HA((sol)) --> K(+)A( (s)(-)) + H-2(g) does not occur via an acid-base pathway, but via elec tron transfer from H- to HA. A model is proposed for the autocatalytic activation of acid-base reaction due to the presence of a superficial layer of adsorbed K+ A(-) ionic pairs. The effect of these ionic pair s is to reduce the activation energy for the acid-base pathway. This m odel predicts that in some conditions the production rate of H-2 forme d via the acid-base pathway oscillates with time.