Oxide−Metal Nanowires by Oxidation of a One-Dimensional Mn−Pd Alloy: Stability and Reactivity

Abstract

Distinct one-dimensional (1D) oxide nanowires decorating the step edges of a stepped Pd(1 1 9) surface are formed by partial and complete oxidation of a 1D Mn-Pd alloy. Under full postoxidation treatment at 470-570 K, 1D MnO(2) nanowires coupled pseudomorphically to the Pd steps are obtained. Oxidized nanowires, which maintain the basic structural pattern of the 1D Mn-Pd alloy, are instead prepared by exposure of the Mn-Pd alloy to O(2) at 90 K and subsequent short heating to 400 K. A relatively weak Mn-O bonding characterizes these oxidized alloy wires, which are readily reduced by reaction with CO at moderate temperature (350 K). The here reported system emphasizes the influence of kinetic constraints in the formation of oxide nanostructures.

Structure and Electronic Properties of CoO Nanostructures on a Vicinal Pd(100) Surface

“…In addition to the embedded CoO x structures, rod-like features of approximately 1 nm in length are attached periodically to the outer step edges (see arrows and ellipses in Figure b,d). Oxidic nanowires of strictly monatomic width, as they have been observed for NiO x and MnO x decorating the steps of vicinal Rh , and Pd , surfaces, respectively, have not been detected for CoO x : the narrowest decoration features observed here are double rows of CoO x .…”

“…The reduced atomic coordination in two-dimensional (2-D) layers or in one-dimensional (1-D) atom chains together with the coupling to a given substrate and the proximity of the respective interfaces have profound consequences for the structural, electronic, magnetic, and chemical response of these structures. − The local electronic configuration of low-coordinated atomic ensembles imprints particular chemical properties on to the nanostructures, which can be exploited in the catalytic performance of such systems . The preparation of well-defined ensembles of 1-D and 2-D systems by atomic engineering using self-assembly techniques on suitable substrates has been established and has been applied successfully to metallic systems. , The use of vicinal metal surfaces as a natural template for the epitaxial growth of 1-D structures via step decoration is a suitable preparation strategy and has been employed to fabricate metallic 1-D nanowires. , The fabrication of 1-D oxide systems using similar bottom-up procedures typically requires a more complex multistep preparation recipe but has also been achieved recently. − The resulting oxide nanowires of atomic widths, coupled elastically and electronically to the steps of a different metallic host, constitute a quasi-1-D oxide–metal hybrid system, which provides excellent model character for studies of advanced catalysis . Indeed, the steps of metallic Cu nanoparticles decorated with a ZnO phase have very recently been identified as the active sites in an industrial catalyst for methanol synthesis .…”

Structure–Property Relationship and Chemical Aspects of Oxide–Metal Hybrid Nanostructures

“…The exclusive oxidation of the Ni rows is made possible by the enhanced chemical reactivity toward oxygen of the coupled Rh–Ni nanowires at the steps, which form 1D NiO 2 lines after oxidation as evidenced by STM, XPS, and screened hybrid DFT analysis . Mn oxide nanowires have also been successfully fabricated on vicinal surfaces of Pd(100). , Figure a displays an STM image of monatomic rows of Mn oxide nanowires decorating the step edges of a Pd(1 1 17) surface; they have been prepared by deposition of 0.1 ML Mn at 300 K followed by oxidation in 1 × 10 –8 mbar oxygen at 470 K. The MnO x nanowires are readily recognized at the step edges by their brighter contrast in STM, while at the (100) terraces a p(2 × 2) structure of chemisorbed oxygen is visible. The monatomic MnO x rows are attached to the Pd steps in a (×1) periodicity, thus they are pseudomorphically coupled, and their formal stoichiometry is MnO 2 , with every Mn atom coordinated to four O atoms, two at the lower and two at the upper step edge, as indicated by DFT calculations .…”

Monatomic Co, CoO2 , and CoO3 nanowires on Ir(100) and Pt(100) surfaces: Formation, structure, and energetics

“…1. Until now, related TMO chain structures could only be prepared via step decoration of vicinal surfaces [11][12][13] , where the density and in particular the degree of long range order is rather limited. In contrast, the high density of one-dimensional TMO chains leads to a maxi-mum of metal/oxide interfaces for the given surface area and can therefore be regarded as a model system for an extremely dispersed case of a bifunctional TMO-noble metal system.…”