Electronic, Structural, and Reactive Properties of Ultrathin Aluminum Oxide Films on Pt(111)

Abstract

Low-energy electron diffraction, X-ray photoelectron spectroscopy, high-resolution electron energy-loss spectroscopy, scanning tunneling microscopy, and temperature-programmed reaction spectrometry results are reported for the structural and reactive behavior of alumina films grown on Pt(111) as a function of thickness and oxidation temperature. Submonolayer Al films undergo compete oxidation at 300 K, annealing at 1100 K resulting in formation of somewhat distorted crystalline γ-alumina. Thicker deposits require 800 K oxidation to produce Al2O3, and these too undergo crystallization at 800 K, yielding islands of apparently undistorted γ-alumina on the Pt(111) surface. Oxidation of a p(2 × 2) Pt3Al surface alloy occurs only at >800 K, resulting in Al extraction. These alumina films on Pt(111) markedly increase the coverage of adsorbed SO4 resulting from SO2 chemisorption onto oxygen-precovered surfaces. This results in enhanced propane uptake and subsequent reactivity relative to SO4/Pt(111). A bifunctional mechanism is proposed to account for our observations, and the relevance of these to an understanding of the corresponding dispersed systems is discussed.

Sulfur as a catalyst promoter or selectivity modifier in heterogeneous catalysis

“…In addition, the formation of an aluminium sulfate phase is thought to activate dissociative chemisorption of propane which enhances the ease of oxidation suggesting that sulfur may have more than one function (i.e., modifying the active metal and the support). 95 The belief that sulfur modifies both the metal and support contrasts with other literature where only the support and metal-support interface are thought to be modified. [89][90][91] In addition to the use of propane to represent hydrocarbon automotive exhausts, methane is also known to be present, and in fact, the added challenge of removing this from vehicle exhausts has, since 2009, led to a new emission standard described as non-methane hydrocarbons (NMHC).…”

Photoemission study of Al adlayers on Mn

“…To fabricate these devices, one requires the control of the growth modes adopted by thin films deposited on a substrate. [1][2][3][4][5][6][7][8][9][10][11] It is quite remarkable that the substrate plays an important role in the electronic properties of metallic adlayers where the interactions with the substrate material are crucial. [1][2][3][4][5] This can provide valuable information about the growth modes of thin films and intermixing phenomena at the interfaces.…”

“…In general, the properties of low dimensional systems, e.g., ultrathin films and surface alloys, can be quite different from their bulk properties. [6][7][8][9][10][11] It was shown that the metals deposited on substrate can occupy the topmost surface sites, diffuse into the subsurface, and alloy formation occurs at the intermixed regime of bimetallic surfaces. 12 The migration of Al atoms and formation of complex surface alloy phases were observed by using scanning tunneling microscopy (STM).…”

Structure of monolayer tin oxide films on Pt(111) formed usingNO2as an efficient oxidant

“…One such example is the growth of FeO on Pt͑111͒. [10][11][12][13][14] Some of these novel materials exhibit unique electronic 15,16 and/or ferromagnetic properties. 17 Furthermore, bulk oxides often lack stable polar surfaces, but these surfaces may also be stabilized on ultrathin films.…”