Adsorption and reaction of ethyl fragments on reduced and oxidized silica-supported copper particles

Infrared spectroscopy and temperature programmed desorption have been used to investigate the adsorption and reaction of ethyl fragments, from the dissociative adsorption of ethyl chloride and ethyl bromide, on reduced- and oxidized-Cu/SiO₂. On reduced-Cu/SiO₂, ethyl chloride dissociates at room temperature to form adsorbed ethyl fragments on the copper particle surface. In addition, ethyl fragments can spill over onto the silica support where they undergo reaction with the SiOH groups to form SiOCH₂-CH₃. The reaction chemistry of these adsorbed hydrocarbon fragments was followed as a function of temperature from 300 to 1100 K. Propane, ethylene, ethane, and methane evolve from reaction of ethyl fragments on the copper particle surface below 500 K. The distribution of these products on reducedCu/SiO₂ is found to depend on sample preparation. On oxidized-Cu/SiO₂, both C-Br and C-C bond dissociation in adsorbed ethyl bromide occur at room temperature. As determined by infrared spectroscopy, reaction of hydrocarbon fragments with surface oxygen atoms leads to the formation of adsorbed ethoxide, methoxide, and bidentate formate. Formaldehyde and acetaldehyde evolve from oxidized-Cu/SiO₂ near 550 and 410 K, respectively; ethylene, CO, and CO₂ form as well. Possible mechanisms for the formation of adsorbed and gas-phase products from C₂H₅X adsorption and reaction on reduced- and oxidized-Cu/SiO₂ are discussed.