Generation and Reactions of CH2 and C2H5 Species on Mo2C/Mo(111) Surface

Abstract

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 photoelectron, Auger electron, and temperature programmed desorption spectroscopies. Independently of the coverage, CH2I2 adsorbs molecularly at 90–100 K. The dissociation of an adsorbed layer starts around 180–190 K. The primary products of thermal dissociation are adsorbed CH2 and I. The species CH2 undergoes self-hydrogenation to CH4 at Tp=300 K and dimerization into C2H4 at and above 222–280 K. Ethylene formed desorbs above 400 K. C2H5I also adsorbs molecularly on Mo2C at 90–100 K and dissociates to C2H5 and I above 150 K. The reaction of C2H5 on Mo2C/Mo(111) surface yielding C2H6 and C2H4 proceeds at a much lower temperature, above 180 K, than that of CH2. Neither the cleavage of the C–C bond nor the coupling of C2 compounds occurred to detectable extent under the reaction conditions. The ethylene formed in the reactions of both CHx species exhibited the same features as observed following C2H4 adsorption on Mo2C: the stable di-σ-bonded ethylene is transformed into ethylidyne at higher temperature. The results are discussed in relevance to the conversion of methane into benzene on Mo2C deposited on ZSM-5.