Surface Chemistry of Chloroiodomethane, Coadsorbed with H and O, on Pt(111)

Abstract

Using temperature programmed desorption (TPD), predosed oxygen TPD (POTPD), high-resolution electron energy loss spectroscopy (HREELS), and Auger electron and X-ray photoelectron spectroscopy (AES and XPS), we have investigated the chemistry of chloroiodomethane (ClCH{sub 2}I) dosed onto clean, D-covered and O-covered Pt(111). At or below 100 K, ClCH{sub 2}I adsorbs molecularly on all these surfaces. While ClCH{sub 2}I in physisorbed multilayers desorbs reversibly, a significant portion in the first monolayer dissociates during heating. In the presence of coadsorbed D, methane formation is enhanced and there is a H-for-D exchange reaction involving C-H bonds. In the presence of coadsorbed O, besides H{sub 2}O, CO and CO{sub 2}, formaldehyde (H{sub 2}CO) is produced during TPD. In addition. there is a new reaction channel - chlorination to form CH{sub 2}Cl{sub 2}, which does not occur in the absence of O. To our knowledge, this is the first report of formaldehyde produced by the oxidation of a CH{sub 2} precursor on Pt(111). Reaction paths are discussed, as are the effects of coadsorbed halogen atoms on hydrogenation, C-C coupling, and oxidation of CH{sub 2}. 101 refs., 20 figs., 5 tabs.