Molecularly resolved studies of the reactions of amines with Cu(110) surfaces

The interaction of with clean, partially oxidised and fully oxidised Cu(110) surfaces has been studied by XPS and STM at room temperature and is compared to the reactions of 2-tertbutylaniline. Limited dissociation occurs at clean Cu(110), but at a partially oxidised surface, a chemisorbed phenylimide ((C6I I>N(a)) product is formed, together with water which desorbs. The phenyl imide forms three different (4 ()W 4 (A (4 0) domains, described by, and unit meshes. A coadsorption y2 2) y- 2) 2) of aniline and dioxygen in a 300:1 mixture results two structures, described by (3) f3 and unit meshes. In both cases, the maximum surface l-i V U V concentration predicted by STM is half that actually determined by quantification of the XPS peaks. Pi-stacking of the phenyl rings is proposed to account for this discrepancy. 2-tertbutylaniline adsorbs at partially oxidised Cu(l 10) surfaces, forming a moderately ordered p(2x2) structure. The maximum surface coverage predicted by STM is in agreement with the actual maximum surface concentration of 2.5 x 1014cm'2. The interaction of dimethylamine with clean, partially oxidised and fully oxidised Cu(110) surface at room temperature has been studied by STM and XPS. Reaction with partially oxidised Cu(110) causes reconstruction of the chemisorbed oxygen islands from the well know p(2xl)-0(a) structure to a (3x1) phase. The expanded oxygen islands desorb as water and structures orientated in the <110> direction, assigned to (CH3)2N, form in their place. The structures are stable for several minutes, after which they desorb, possibly as CIl3NCH2(g) via a P-elimination reaction. Reaction with a complete O(a) monolayer results in limited dimethylamine adsorption. Dimethylamine does not react with clean Cu(110) at room temperature. The reaction of ethylamine with clean, partially oxidized and fully oxidized Cu(110) has been studied by STM and XPS at room temperature and is compared with the reactions of diaminoethane and 2,2,2-trifluoroethylamine. Kthylamine reacts with partially oxidized Cu(110) causing expansion of the oxygen islands from p(2xl) to (3x1) structures. After a period of several minutes, the expanded oxygen islands desorb as water, leaving a clean surface. Kthylamine reacts with a full O(a) monolayer without any reconstruction, causing desorption of all surface oxygen and resulting in a clean surface. It is proposed that the ethylamine desorbs as CM3CI INI I via a p-elimination reaction. Diaminoethane reacts with partially oxidized Cu(110) in the exact same manner as ethylamine. At partially oxidized Cu(110), 2,2,2- trifluorethylamine causes desorption of all chcmisorbcd oxygen without causing any reconstruction of the oxygen islands. A clean surface is left at the end of the reaction. A full O(a) monolayer is inert to 2,2,2-trifluorethylamine. The interaction of 4,4-diaminobenzophenone, (I bNCV ICO, with clean Cu(110) surfaces has been investigated by STM and XPS at room temperature. Sub-monolayer coverages give rise to three distinct, highly ordered structures. The first can be described using by a unit mesh. 1 he others are based around a pair of (7) (7) molecules, forming and lattices. Above a monolayer, order breaks down

Fabrication of complex model oxide catalysts: Mo oxide supported on Fe3O4(111)

Industrial catalysts for the oxidation of methanol to formaldehyde consist of iron molybdate [Fe2(MoO4)3]. Using a variety of techniques we have previously shown that the surface of these catalysts is segregated in MoO3, and in order to understand the relationship between surface structure and reactivity for these systems we have begun a surface science study of this system using model, single crystal oxides. Model catalysts of molybdenum oxide nanoparticles and films on an Fe3O4 (111) single crystal were fabricated by the hot-filament metal oxide deposition technique (HFMOD), where molybdenum oxides were produced using a molybdenum filament heated in an oxygen atmosphere. Low energy electron diffraction (LEED), X-ray photoelectron spectroscopy (XPS), and scanning tunnelling microscopy (STM) have been used to investigate molybdenum oxide nanoparticles and films deposited on Fe3O4 (111). The molybdenum oxide film forms in the highest oxidation state, 6+, and is remarkably stable to thermal treatment, remaining on the surface to at least 973 K. However, above ~ 573 K cation mixing begins to occur, forming an iron molybdate structure, but the process is strongly Mo coverage dependent

Fabrication of complex model oxide catalysts: Mo oxide supported on Fe3O4(111)

Industrial catalysts for the oxidation of methanol to formaldehyde consist of iron molybdate [Fe2(MoO4)3]. Using a variety of techniques we have previously shown that the surface of these catalysts is segregated in MoO3, and in order to understand the relationship between surface structure and reactivity for these systems we have begun a surface science study of this system using model, single crystal oxides. Model catalysts of molybdenum oxide nanoparticles and films on an Fe3O4 (111) single crystal were fabricated by the hot-filament metal oxide deposition technique (HFMOD), where molybdenum oxides were produced using a molybdenum filament heated in an oxygen atmosphere. Low energy electron diffraction (LEED), X-ray photoelectron spectroscopy (XPS), and scanning tunnelling microscopy (STM) have been used to investigate molybdenum oxide nanoparticles and films deposited on Fe3O4 (111). The molybdenum oxide film forms in the highest oxidation state, 6+, and is remarkably stable to thermal treatment, remaining on the surface to at least 973 K. However, above ~ 573 K cation mixing begins to occur, forming an iron molybdate structure, but the process is strongly Mo coverage dependent

Possible role for Cu(II) compounds in the oxidation of malonyl dichloride and HCl at Cu(110) surfaces

The pathway for the chlorination of Cu(110) surfaces by malonyl dichloride and HCl is changed in the presence of oxygen with STM results suggesting the formation of a surface CuCl2 state at room temperature that may have implications for mechanistic models of the Deacon process and of dioxin formation at aerosol particle surfaces

Molecularly resolved studies of the role of basicity in the reaction of amines with oxygen at a Cu(110) surface

The role of basicity in the surface reactions of amines has been investigated in an STM/XPS study of the oxidation of methylamine, ethylamine and 2,2,2-trifluoroethylamine at a Cu(l 10) surface. Methylamine and ethylamine are strongly basic molecules and for sub monolayer concentrations of oxygen form an amine/oxygen complex characterised by a (3 x 1) structure. The complex rapidly decomposes at room temperature to form water and an imide which desorbs via beta-elimination. In contrast, 2,2,2-trifluoroethylamine has a relatively low basicity and its reactions with surface oxygen do not involve a stable intermediate. (c) 2007 Elsevier B.V. All rights reserved

Aromatic interactions in the close packing of phenyl-imides at Cu(110) surfaces

The oxidation of aniline at Cu(1 1 0) surfaces at 290 K has been studied by XPS and STM. A single chemisorbed product, assigned to a phenyl imide (C6H5N(a)), is formed together with water which desorbs. Reaction with preadsorbed oxygen results in a maximum surface concentration of phenyl imide of 2.8 × 1014 mol cm−2 and a surface dominated by domains of three structures described by , and unit meshes. However, concentrations of phenyl imide of up to 3.3 × 1014 mol cm−2 were obtained from the coadsorption of aniline and dioxygen (300:1 mixture) resulting in a highly ordered biphasic structure with and domains. Comparison of the STM and XPS data shows that only half the phenyl imides at the surface are imaged. Pi-stacking of the phenyl rings is proposed to account for this observation

STM and XPS Studies of the Oxidation of Aniline at Cu(110) Surfaces

Aniline chemisorption at clean and partially oxidized Cu(110) surfaces at 293 K is compared with the reaction of a 300:1 aniline/dioxygen mixture at the same surface using STM and XPS. Limited dissociation occurs at the clean surface but in the presence of chemisorbed oxygen efficient oxy-dehydrogenation takes place with water desorption and the formation of chemisorbed phenyl imide (C6H5N(a)) with a reaction stoichiometry that changes with coverage. The adsorption site of the phenyl group is identified by STM to be the 2-fold hollow and it is proposed that the nitrogen is situated over the short bridge site. Chemisorptive replacement of oxygen gives a maximum phenyl imide concentration of 2.8 × 1014 molecules cm-2 at which coverage the surface is dominated by a mixture of three ordered domains with structures described by , , and unit meshes. Adsorption of aniline and dioxygen mixtures however results in phenyl imide concentrations up to 3.4 × 1014 cm-2 molecules cm-2 and a highly ordered biphasic structure characterized by and domains. A discrepancy between the concentrations measured by XPS and those calculated from the STM structures is discussed in terms of π-stacking of the phenyl rings in the adsorbed monolayer. Finally the chemistry of aniline is compared with that of ammonia and the importance of the NH bond strength and the basicity of the amine discussed