Infrared studies of ethene hydrogenation over ZrO2. Part 2.—Ethane adsorption

Abstract

Infrared spectra of adsorbed ethane have been examined following on from those of ethene determined in a previous study of ethene hydrogenation. Two types of adsorbed ethane were identified from IR spectra. A strongly adsorbed ‘end-on’ species had its C—C bond inclined to the ZrO₂ surface with one methyl interacting with the surface and showed a softened CH stretch band at 2798 cm^–1(2119 cm^–1 in the case of CD stretch band of C₂H₅D). This species irreversibly adsorbs up to 253 K. Another weakly adsorbed ‘side-on’ species of ethane was observed below 193 K. This species seems to adsorb with its two methyls equivalent on the ZrO₂ surface, which was concluded from its CH stretch bands observed in almost the same region as those of the free molecule.

The interaction of adsorbed ethane with the surface OH species has also been studied as in the case of ethene adsorption. This interaction was observed as reverse peaks of OH species (shifted to hydrogen-bonded peaks). About 30% of the remaining OH species even after evacuation at 1023 K was observed to interact with adsorbed ethane while 100% interacted in the case of ethene adsorption. It has also become clear that the intentionally produced OH species obstruct the adsorption sites of ethane, especially that of the strongly adsorbed end-on species.