Infrared study of ZrO2 surface sites using adsorbed probe molecules.: 2.: Dimethyl ether adsorption

The properties of two types of surface OH species, terminal (t) and bridged (b), as well as corresponding vacant sites on ZrO2 at 573 K have been studied using dimethyl ether (DME) adsorption as an IR molecular probe. On the dehydroxylated ZrO2 surface, the molecularly adsorbed CH3OCH3 species was' dissociated moderately. On the other hand, the molecularly adsorbed CH3OCH3 species was not observed on the fully hydroxylated ZrO2 surface because of the rapid dissociation of CH3OCH3. Kinetic analysis revealed that the activity of the dissociative adsorption of DME on surface sites is in the order t-OH sites > vacant sites > b-OH. sites on ZrO2, which parallels that of the adsorption of pyridine, CO2, and HCOOH at the same sites, as reported previously. Furthermore, the surface t-(OH)-O-18 species has been found to provide active O-18 atoms for the dissociation of CH3OCH3 to OCH3 and (OCH3)-O-18 species at 573 K, which shows that the (OH)-O-18 species is involved in the dissociation of DME. We suppose that the nucleophilic adsorption of DME to replace t-OH species occurs at t-HO-Zr sites and that the release of t-OH species is favorable for the dissociation of DME. This is consistent with the results of the adsorption of pyridine, CO2, and HCOOH, demonstrating a characteristic of acidic and basic bifunctions of t-HO-Zr sites.