Infrared Study of ZrO_2 Surface ites Using Adsorbed Probe Molecules.2.Dimethyl Ether Adsorption

摘要

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 CH30CH3 species was dissociated moderately. On the other hand, the molecularly adsorbed CH3OCH3 species was not observed on the fully hydroxylateG Zr02 surface because of the rapid dissociation of CH30CH3. Kinetic analysis revealed that the activity of the dissociative adsorption of DMEon surface sites is in the order t-OH sites > vacant sites > b-OH sites on zrO2, which parallels that of the adsorption of pyridine, C02, and HCOOH ~t the same sites, as reported previously. Furthermore, the surface t-180H species has been found to provide active 180 atoms for the dissociation of CH30CH3 to OCH3 and 180CH3 species at 573 K, which shows that the 180H species is involved in the dissociation of DME. We suppose that the nucleophilic adsorption of DME to replace t-QH species occurs at t-HO-Zr sites and that the release of t-Ol:1 species is favorable for the dissociation .of DME. This is consistent with the results of the adsorption of pyridine, C02, and HCOOH, demonstrating a characteristic of acidic and basic bifunctions oftOH-Zr sites.