Gas-phase atomic hydrogen induced carbon-carbon bond activation in cyclopropane on the Pt(111) surface

Carbon-carbon bond activation in adsorbed cyclopropane is observed following exposure to gas-phase atomic hydrogen on the Pt(111) surface for temperatures as low as 120 K despite the fact that this low index platinum surface generally does not activate C-C bonds. Cyclopropane desorbs molecularly at 140 K. In the presence of coadsorbed hydrogen, no reaction with cyclopropane is observed. In contrast, gas-phase atomic hydrogen reacts with cyclopropane at 120 K to form a propyl intermediate. During subsequent heating, this intermediate is hydrogenated to form propane at 170, 190, and 220 K. As indicated by the lack of methane and ethane formation, no multiple C-C bond activation processes were observed. Reaction mechanisms are proposed for each new TPRS peak observed based upon the products observed, isotope experiments, and comparisons with the literature. The primary 170 K propane peak is caused by surface hydrogenation of an adsorbed propyl formed by C-C bond activation in adsorbed cyclopropane by gas-phase atomic hydrogen. The 190 It propane peak is caused by reaction between adsorbed cyclopropane and a new reactive form of adsorbed hydrogen. The propane peak at 220 K is dominant only for low gas-phase atomic hydrogen exposures and may be associated with a coverage-dependent reaction path Taken together, these results clearly indicate that the reaction between gas-phase atomic hydrogen and cyclopropane is more complex on the Pt(111) surface than the analogous reaction on the Ni(100) surface where only one propane peak was reported. Prolonged exposures of the clean Pt(111) surface to gas-phase atomic hydrogen at 120 K resulted in an unusually low-temperature state of hydrogen that desorbs below 220 K, causes carbon-carbon bond activation, and has not previously been reported.