ETHYLENE HYDROGENATION ON FCC FE THIN-FILMS GROWN ON THE RH(100) SURFACE

Ethylene hydrogenation on fee Fe thin films grown on the Rh(100) surfa ce has been studied as a Function of film thickness by UPS and TPRS. W ith the increase of Fe coverage from 1 to 3 ML, the H-2 desorption tem perature shifted from 210 to 270 K, in accordance with the growth of t he electronic density of stales just below the Fermi level. In TPR spe ctra from ethylene adsorbed at 80 K on the clean Fe thin films, ethyle ne desorbed at 230 K, although two desorption slates were observed al 110 and 210 K for the adsorption of ethylene on H-precovered Fe thin f ilms. Ethane formation is observed from weakly adsorbed ethylene with the destabilized H atoms characteristic of the Fe thin film of 1 ML. T his clearly shows that the bonding of Fe-H as well as the state of ads orbed ethylene plays an important role in ethylene hydrogenation. (C) 1997 Elsevier Science B.V.