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.