Spatially Nonuniform Reaction Rates during Selective Oxidation on Gold

Abstract

The nonuniform reactivity of adsorbed oxygen during the selective oxidation of methanol on Au(110)-(1×2) was demonstrated using in situ scanning tunneling microscopy (STM), establishing the importance of both atomic and mesoscale structure in determining reaction kinetics. At coverages above 0.06 ML, oxygen consumption occurs preferentially along [11̅0] direction, creating local regions completely devoid of oxygen between oxygen islands. The directionally specific reactivity is attributed to a combination of the weaker binding of oxygen atoms at chain termini and the release of surface strain induced by O bonding to Au. The generality of this phenomenon is illustrated by analogous, but kinetically contrasting behavior, for reaction of 2-propanol with oxygen covered Au(110)-(1×2). Even at low O coverages, there are structurally related changes in the reactivity for the reaction with methanol. With decreasing O coverage, a slow reaction period is followed by a fast reaction period, the latter starting when oxygen coverage decreases to ∼0.06 monolayer, independent of the initial coverage. This increase in reactivity is attributed to a sudden destabilization of the island structure. These results demonstrate that both local and mesocale structures can affect reactivity.

Facile Decomposition of Organophosphonates by Dual Lewis Sites on a Fe3O4(111) Film

“…Scanning tunneling microscopy (STM) was performed in a commercial Omicron VT Beam Deflection atomic force microscopy/STM system as described previously. , The single crystal was mounted on a standard flag-style single layer sample plate, and a Pt–Ir tip was used for the STM experiments. The same set of preparation cycles lead to a clean and flat Fe 3 O 4 (111)/Fe 2 O 3 (0001) surface, as evidenced by LEED and STM images.…”

High Density of End-Oxygens Induced by NO Adsorption on (2 × 1)Ni–O/Ni(110) Surfaces

“…However, to date, how to effectively increase the end-O density is still a challenging task. In previous reports, ,, the surface end-O structures are produced by direct adsorption of O 2 , O, or O 3 on TM surfaces. In this way, the produced M–O short chains are not uniform and distributed randomly, and the end-O density is not high enough which suppresses the acquisition of OH at desired sites and the desired reaction rates on the surface. , …”

“…Oxygen covering can modify the surface morphologies and the electronic structures of transition metals (TM) and consequently alter their chemical reactivity. − Therefore, the precise regulation of the oxygen coverage (θ O ) on TM surfaces is expected to yield the most optimized catalytic activity. Taking the Ni(110) surface for example: when θ O is lower than ∼0.25 monolayer (ML), the surface exhibits a high reactivity for the capture of protons from H 2 O or NH 4 to form OH. , When θ O exceeds this critical value, the Ni(110) surface becomes inert sharply.…”

“…Taking the Ni(110) surface for example: when θ O is lower than ∼0.25 monolayer (ML), the surface exhibits a high reactivity for the capture of protons from H 2 O or NH 4 to form OH. , When θ O exceeds this critical value, the Ni(110) surface becomes inert sharply. Such a rule is also appropriate for other TM surfaces, such as Cu, Ag, Au, Pd, and Fe, for the decomposition of H-contained molecules like H 2 O, − NH 4 , ,− and alcohols ,− and for the oxidization of reductive gases like CO. , …”

“…The altering of TM surface reactivity by oxygen covering is related to the density of end-oxygens (end-O) on the TM surfaces. ,, At low θ O , numerous metal–oxygen (M–O) short chains are formed initially, and thus, there are numerous end-O at the numerous M–O chain ends. The end-O are weakly bonded to the TM surfaces and possess more dangling bonds, thus exhibiting the higher reactivity. As the surface θ O exceeds the critical value (∼0.25 ML), the short M–O chains grow quickly into long chains and the number of end-O is thus decreased sharply, which causes a sharp decrease in the surface reactivity.…”