The adsorption and dissociation of CH2I2 and C2H5I on Mo2C/Mo(111) surface
have been investigated with the purpose of producing adsorbed CH2 and C2H5
species. Methods used include high resolution electron energy loss, X-ray p
hotoelectron, Auger electron, and temperature programmed desorption spectro
scopies. Independently of the coverage, CH2I2 adsorbs molecularly at 90-100
K. The dissociation of an adsorbed layer starts around 180-190 K. The prim
ary products of thermal dissociation are adsorbed CH2 and I. The species CH
2 undergoes self-hydrogenation to CH4 at T-p = 300 K and dimerization into
C2H4 at and above 222-280 K. Ethylene formed desorbs above 400 K. C2H5I als
o adsorbs molecularly on Mo2C at 90-100 K and dissociates to C2H5 and I abo
ve 150 K. The reaction of C2H5 on Mo2C/Mo(111) surface yielding C2H6 and C2
H4 proceeds at a much lower temperature, above 180 K, than that of CH2. Nei
ther the cleavage of the C-C bond nor the coupling of C-2 compounds occurre
d to detectable extent under the reaction conditions. The ethylene formed i
n the reactions of both CHx species exhibited the same features as observed
following C2H4 adsorption on Mo2C: the stable di-sigma-bonded ethylene is
transformed into ethylidyne at higher temperature. The results are discusse
d in relevance to the conversion of methane into benzene on Mo2C deposited
on ZSM-5. (C) 1999 Academic Press.