Infrared studies of ethene hydrogenation over ZrO2. Part 1.—Ethene adsorption

Abstract

Adsorption species of ethene over ZrO₂ have been observed by Fourier-transform infrared spectroscopy (FTIR). Three different species were identified from IR spectroscopic analysis; physically adsorbed, π-bonded and strongly π-bonded (s-π-bonded) ethene. s-π-bonded ethene is adsorbed more stably than π-bonded ethene. The physically adsorbed species was observed below 173 K with strong bands of IR-active modes and very weak bands of IR-inactive ones for free molecules. Both π-bonded and s-π-bonded ethene show common bands at 1446 (CH₂ asym. scissoring) and 993–1007 cm^–1(CH out of plane bend), and are produced below 275 and 373 K, respectively. s-π-bonded ethene is characterized by four bands in the CH stretch region (3091, 3079, 2989 and 2962 cm^–1) and additional bands at 1606 cm^–1(CC stretch) and 1338 cm^–1(CH₂ sym. scissoring). The adsorption and desorption behaviour of these two species were examined with use of bands at 1446 and 1338 cm^–1. The dependence on temperature of the amounts of both species adsorbed and on the amounts of surface OH species were studied in detail.