A comparison of the catalytic activity of liquid and solid surfaces. The decomposition of methanol on solid and liquid zinc

Abstract

On account of its importance from the theoretical and practical standpoints, there has been a great deal of speculation regarding the nature of catalyst surfaces. There is a considerable body of experimental evidence which has led to the assumption that catalyst surfaces are not uniformly active. The main lines of evidence which have led to this conclusion are ( a ) the ease with which the activity of a catalyst is destroyed by heating; ( b ) the poisoning of catalysts by the adsorption of amounts of foreign materials which are not sufficient to cover more than a fraction of the surface; ( c ) the fact that heats of adsorption vary with the amount of material adsorbed. The above evidence makes it highly probable that in some reactions on certain catalysts the surfaces is not uniformly active. As a result a number of theories have been proposed which assign the activity of a solid catalyst to some one limited portion of the surface. The most important of these are the original theory of Taylor in which the "active centres" are identified with peaks or extra-lattice atoms on the surface, and that of Schwab which assigns the activity to crystal boundaries and microcrystalline imperfections.