Behaviour of chemisorbed hydrogen under reaction conditions and the mechanism of the H2—D2 exchange reaction over zinc oxide

Abstract

The mechanism of the low-temperature H₂—D₂ exchange reaction over ZnO at lower temperatures was studied using volumetric adsorption during the reaction as well as the infrared spectroscopic technique. It is concluded that at lower temperatures chemisorbed hydrogen, as ZnH and ZnOH, observed by the infra-red technique, behaves similarly to that measured volumetrically, and is in fact the reaction intermediate for the exchange reaction. A marked kinetic isotope effect was observed in the exchange reaction, although no kinetic isotope effect is involved in hydrogen adsorption on ZnO. The exchange reaction over ZnO proceeds mainly via the interaction between chemisorbed hydrogen on the surface and hydrogen molecules in the ambient gas. In other words, the Eley-Rideal mechanism predominates.