Ethyl chloride decomposition on oxide-supported platinum catalysts

Ethyl chloride decomposition on Pt/SiO₂ and Pt/Al₂O₃ catalysts has been investigated by infrared spectroscopy and mass spectrometry. Ethyl chloride reacts on Pt particles at low temperatures near 200 K to form adsorbed C₂ hydrocarbon fragments. By comparison to literature infrared spectra, three species are identified to be adsorbed on the Pt catalysts-ethyl (C₂H₅), ethylene (C₂H₄), and ethylidyne (C₂H₃). The C₂H_x species coexist to a greater extent on the surface of the Pt particles than on single crystal Pt surfaces. The infrared data suggest there are two different reaction pathways that ethyl chloride may undergo on the Pt particles. The first reaction pathway involves α,β-elimination of HCl to give adsorbed ethylene. The second reaction pathway results from C-Cl bond dissociation to give adsorbed ethyl groups and chlorine atoms. Adsorbed ethyl groups dehydrogenate to ethylidyne upon warming. In the presence of hydrogen, C₂ fragments can be hydrogenated to give ethane. The data show that adsorbed ethyl and ethylene hydrogenate much more readily than ethylidyne. At higher temperatures near 473 K, ethyl chloride reacts on Pt/SiO₂ and Pt/Al₂O₃ to yield gas-phase ethylene, ethane, methane, and hydrogen chloride. The reaction rate is enhanced in the presence of hydrogen and there is a greater amount of ethane produced relative to ethylene. Ethyl chloride can react with the oxide support as well at high temperatures. Surface hydroxyl groups on the alumina support react with ethyl chloride to give ethoxy, AlOCH₂CH₃, near 473 K, whereas silica hydroxyl groups show no reaction with ethyl chloride up to 573 K. Possible mechanisms for the high-temperature reaction of ethyl chloride on oxide-supported Pt catalysts are discussed.