Dehalogenation of 1-chloro-1-fluoroethene to acetylene on alpha-Cr_2O_3 (1012)

摘要

The adsorption of CFCl = CH_2 on the nearly stoichiometric Cr_2O_3 (1012) surface results in a 1,1-dihaloelimination reaction to produce acetylene gas, HC ident to CH_(g), and adsorbed chlorine and fluorine. Thermal desorption experiments reveal two acetylene desorption features. The lower temperature acetylene channel is desorption limited (E_a = 92 kJ/mole), while the formation of fluorovinyl and/or vinylidene surface intermediates is suggested by the occurrence of a higher temperature (E_a = 124 kJ/mole) reaction-limited acetylene desorption channel. The deposition of halogen onto the sample surface by the CFCl = CH_2 decomposition reaction was found to initially increase the CFCl = CH_2 sticking coefficient and the activity for halogen coverages up to about one-third and then lead to deactivation at higher halogen coverages due to site blocking of the surface cations. No evidence was seen for the replacement of surface lattice oxygen by halogen under the conditions of this study. Surface that were preexposed to O_2 to site block surface cations with terminal chromyl oxygen were found not to react with CFCl = CH_2.