Dynamic treatment of chemisorbed species by means of infra-red technique. Mechanism of decomposition of formic acid over alumina and silica

Abstract

A new dynamic approach to study chemisorbed species during the course of catalytic reaction was applied to the catalytic dehydration of formic acid over alumina and silica gel. Formic acid is chemisorbed on alumina surface and dissociates to formate ion and a proton. Formate ions on the alumina do not decompose directly to the reaction products and a fraction desorbs rapidly by exchange with formic acid. The rate of the reaction over the alumina is proportional to the number of protons from the dissociative adsorption of formic acid on the alumina surface, and also to the partial pressure of formic acid. Consequently, the decomposition proceeds between formic acid molecules and the surface protons supplied from the dissociative adsorption of formic acid, i.e., protons from formic acid behave as he reaction sites on the catalyst surface, while the formate ion on the catalyst surface does not behave as the reaction intermediate.