Competing pathways for methoxy decomposition on oxygen-covered Mo(110)

Abstract

The reactions of methanol (CH 3 OH) are investigated on a range of oxygen overlayers on Mo͑110͒, with O from ϳ0.5 to Ͼ1 ML, using a combination of vibrational spectroscopies and temperature-programmed reaction. Infrared spectroscopy identifies a common, tilted methoxy intermediate at high temperature on all overlayers studied; electron energy loss spectroscopy shows that this intermediate decomposes to deposit oxygen exclusively in high-coordination sites. While C-O bond scission to evolve gas-phase methyl radicals is the only reaction observed for methoxy on highly oxidized Mo͑110͒, on the surface oxygen overlayers competition between dehydrogenation and methyl evolution is highly sensitive to oxygen coverage. The enhanced selectivity for hydrocarbon formation from methanol reaction on oxygen-modified Mo͑110͒ relative to the clean surface is attributed to inhibition of dehydrogenation pathways rather than to marked changes in the C-O bond potential of methoxy.

Site-Selective Surface Reactions: Nitric Oxide Reduction on Mo(110)

“…[22]. consistent with results for methoxy (CH 3 O) species formed via the reaction of methanol (CH 3 OH) on these same oxygenmodified surfaces: [27] namely, that perturbation of these bond potentials is highly sensitive to local electronic structure at the bonding site but not to the overall extent of surface oxidation. What is different in the NO case, as compared to CH 3 O, is that the dinitrosyl structure is apparently virtually identical on the clean and oxygen-modified Mo(110) surfaces, whereas there is a distinct difference between the bonding of CH 3 O on clean Mo(110) [28] and on Mo(110) with even a small amount (0.5 ML) of preadsorbed oxygen.…”

Stabilization of Nitrosyls by Surface Oxygen: Structure and Reactivity of NO on Oxygen-Modified Mo(110)

“…Preparation and characterization of the oxygen overlayers used in this study have been outlined in detail previously. , Saturation of the Mo(110) crystal with O 2 at ∼100 K, followed by heating to 500 K, results in a surface overlayer of oxygen predominantly in low-symmetry, high-coordination sites . The coverage of this overlayer is ∼0.75 ML, determined by comparison of the O(KLL)/Mo(LMM) Auger ratio with that a surface of known (0.35 ML) oxygen coverage .…”

“…Oxygen (O 2 , 99.998%, Matheson), isotopically labeled oxygen ( 18 O 2 , 95-98% isotopic purity, Cambridge Isotope Labs), nitric oxide (NO, 99.0% minimum purity, Matheson), and isotopically labeled nitric oxide ( 15 NO, 98% isotopic purity, Cambridge Isotope Labs; 15 N 18 O, 99.9% 15 N, 98.4% 18 O, Isotec) were used as received. The 1:1 mixture of 14 NO and 15 NO was prepared in the stainless steel dosing line and stored in a glass equilibration flask, its composition verified by mass spectrometry.…”

Oxygen-inducedp(2×3)reconstruction on Mo(112) studied by LEED and STM

“…This has encouraged the study of the dissociation and adsorption of oxygen, the oxygen-induced structures, and the oxide formation on the stable low-index Mo surfaces. [1][2][3][4][5][6] These studies include the ͑100͒, ͑110͒, and the ͑111͒ single-crystal surfaces.…”