Gas-Phase Atomic Hydrogen Induced Carbon−Carbon Bond Activation in Cyclopropane on the Pt(111) Surface

Abstract

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 K 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 lowtemperature state of hydrogen that desorbs below 220 K, causes carbon-carbon bond activation, and has not previously been reported.

Tetrahydrometalate Species VH2(H2), NbH4, and TaH4: Matrix Infrared Spectra and Quantum Chemical Calculations

“…Synthesis of new transition metal hydrides and hydrogen complexes and understanding their structures and bonding are of fundamental importance for new hydrogen-storage materials and for use in the activation of H–H, C–H, and C–C bonds. − For example terminal tantalum hydrides are extremely reactive, and they can reduce CO 2 to form bridging methylene diolate complexes . Pulse-laser ablation is one of the most promising methods to generate metal polyhydrides and complexes from reactions of reactive metal atoms with H 2 . − Many transition metal hydrides, lanthanide hydrides, and actinide hydrides and their hydrogen complexes have been synthesized for infrared investigation in this research laboratory. − …”

Desulfurization of the Ni(100) Surface Using Gas-Phase Hydrogen Radicals

“…Due to the large potential energy associated with the unpaired electron, gas-phase hydrogen radicals react with adsorbates that do not react with adsorbed hydrogen . Hydrogen radicals have been used in a wide range of reactions including carbon−carbon bond activation in adsorbed cyclopropane, hydrogenation of CC bonds in adsorbed cyclohexene and ethylene, reduction of adsorbed nitrogen to form ammonia, and abstraction of surface carbon through methanation . In addition, gas-phase hydrogen radicals have been shown to populate subsurface hydrogen states in nickel surfaces .…”

Interaction of gas phase atomic hydrogen with Pt(111): Direct evidence for the formation of bulk hydrogen species

“…Because gas phase atomic hydrogen is 218.4 kJ/mol more energetic than molecular hydrogen (1/2 dissociation energy of H 2 ), when interacting with Pt(111), gas phase atomic hydrogen is energetic enough to overcome any activation energy to form all likely adsorbed H ad species (surface H ad species and bulk H ad species), surely including the active species for practical catalytic reactions. Gland et al [21][22][23][24][25] found that gas phase atomic hydrogen can undergo ring-opening reaction directly with cycloalkanes adsorbed on metal single crystal surfaces and that the ring-opening reaction follows Eley-Rideal mechanism. Therefore, even under UHV conditions, interaction of gas phase atomic hydrogen with Pt(111) can lead to the formation of detectable bulk H ad species.…”