Decomposition of Formic Acid on Silver Catalyst —Adsorption Measurement during Surface Catalysis—

Abstract

Abstract The mechanism of the decomposition of formic acid over reduced silver catalyst has been studied by means of the adsorption measurement during surface catalysis. It was found that the decomposition of formic acid on the silver catalyst at 100°C was first order at lower pressures of formic acid, while at medium pressures it was zero order, the reaction rate being independent of the pressures of ambient formic acid; in the first region the amount of adsorbed formic acid was proportional to the pressure of formic acid, and in the second region it was constant, independent of the pressure of formic acid in the ambient gas. The second region corresponds to “saturation” in an ordinary sense. At pressures of formic acid higher than that in the “saturation” region the amount of adsorbed formic acid increases again linearly with the pressure of formic acid. The linear relation between the reaction rate and the amount of formic acid adsorbed during the reaction was observed over the whole range of the pressure of formic acid studied. It is accordingly concluded that a surface unimolecular reaction in terms of the adsorbed formic acid is the ratedetermining step. The exchange reaction of surface formic acid with those in the ambient gas was studied and it was demonstrated all the formic acid in the adsorbed layer accordingly participated in the exchange reaction. The numbers of surface silver atoms occupied by one molecule of adsorbed formic acid at the saturation points at various temperatures are estimated from the number of surface silver atoms and the amount of formic acid adsorbed at the zero-order kinetics. The number of surface silver atoms occupied by one molecule of adsorbed formic acid increases linearly with temperature.