The Effect of Diluents on the Initial Stages of Catalytic Action

Abstract

IT has been long known that the presence of diluent vapours in the reactants depresses the reaction velocity at a catalyst surface. The following quantitative treatment has been confirmed by experiments on the effect of water vapour on the initial stages of the dehydrogenation of alcohol by copper. Let p = the fractional partial pressure of the reactant A, hence 1 - p = the fractional partial pressure of the diluent B. Then the rate at which the reactant molecules arrive at the surface is proportional to, say. Thus the probability that a reactant molecule should bombard a given portion of a catalyst at a given instant is i.e. the fraction of A molecules in the impinging stream of A and B molecules. According to the conception of Langmuir and Frenkel, a molecule that hits another adsorbed molecule is immediately reflected, whereas when it strikes the bare surface it remains for the short period of time r. It is also known that chemical action occurs on definite centres on the catalyst surface.