Bond activation sequence observed in the chemisorption and surface reaction of ethanol on Ni(111)

Abstract

The mechanism of ethanol decomposition on the Ni(111) surface has been investigated between 155 and 500 K. The sequence of bond scission steps which occur as ethanol undergoes dissociative reactions on this surface has been deduced using deuterium and 13C isotopic labels. Bond activation occurs in the order (1) OH, (2) CH 2 (methylene CH), (3) CC, (4) CH 3 (methyl CH). The products observed are CH 3CHO(g), CH 4(g), CO(g), H 2(g) and surface carbon, C(a). The latter species exhibits a carbidic AES lineshape in the temperature range 450 to 670 K, at which temperature it dissolves into the Ni bulk. Acetaldehyde, CH 3CHO, and methane, CH 4, desorb with the same threshold temperature (260–265 K), and the formation of both of these products is controlled by scission of the methylene CH bond (CH 2 group). The CH 3 group is cleaved from the intermediate surface CH 3CHO species to form CH 3(ads). H 2 exhibits a broad, doublet desorption peak from 300 to 450 K. The carbonoxygen bond in ethanol remains intact and CO ultimately desorbs in a single desorption limited process ( T p = 430 K). A small fraction of CO(a) species undergo exchange with the carbidic surface carbon in a minor process observed above 440 K.