Activated O2 dissociation and formation of oxide islands on the Be(0001) surface: Another atomistic model for metal oxidation

By simulating the dissociation of O2 molecules on the Be(0001) surface using the first-principles molecular dynamics approach, we propose a new atomistic model for the surface oxidation of sp metals. In our model, only the dissociation of the first oxygen molecule needs to overcome an energy barrier, while the subsequent oxygen molecules dissociate barrierlessly around the adsorption area. Consequently, oxide islands form on the metal surface, and grow up in a lateral way. We also discover that the firstly dissociated oxygen atoms are not so mobile on the Be(0001) surface, as on the Al(111) surface. Our atomistic model enlarges the knowledge on metal surface oxidations by perfectly explaining the initial stage during the surface oxidation of Be, and might be applicable to some other sp metal surfaces.Comment: 5 pages, 4 figure

Hydrogen migration at restructuring palladium-silver oxide boundaries dramatically enhances reduction rate of silver oxide.

Heterogeneous catalysts are complex materials with multiple interfaces. A critical proposition in exploiting bifunctionality in alloy catalysts is to achieve surface migration across interfaces separating functionally dissimilar regions. Herein, we demonstrate the enhancement of more than 104 in the rate of molecular hydrogen reduction of a silver surface oxide in the presence of palladium oxide compared to pure silver oxide resulting from the transfer of atomic hydrogen from palladium oxide islands onto the surrounding surface formed from oxidation of a palladium-silver alloy. The palladium-silver interface also dynamically restructures during reduction, resulting in silver-palladium intermixing. This study clearly demonstrates the migration of reaction intermediates and catalyst material across surface interfacial boundaries in alloys with a significant effect on surface reactivity, having broad implications for the catalytic function of bimetallic materials

Identifying key descriptors in surface binding: interplay of surface anchoring and intermolecular interactions for carboxylates on Au(110)† †Electronic supplementary information (ESI) available: Supporting experimental methods and supporting discussion are included in the supplementary information. See DOI: 10.1039/c7sc05313d

The relative stability of carboxylates on Au(110) was investigated as part of a comprehensive study of adsorbate binding on Group IB metals that can be used to predict and understand how to control reactivity in heterogeneous catalysis. The binding efficacy of carboxylates is only weakly dependent on alkyl chain length for relatively short-chain molecules, as demonstrated using quantitative temperature-programmed reaction spectroscopy. Corresponding density functional theory (DFT) calculations demonstrated that the bidentate anchoring geometry is rigid and restricts the amount of additional stabilization through adsorbate-surface van der Waals (vdW) interactions which control stability for alkoxides. A combination of scanning tunneling microscopy (STM) and low-energy electron diffraction (LEED) shows that carboxylates form dense local islands on Au(110). Complementary DFT calculations demonstrate that adsorbate–adsorbate interactions provide additional stabilization that increases as a function of alkyl chain length for C2 and C3 carboxylates. Hence, overall stability is generally a function of the anchoring group to the surface and the inter-adsorbate interaction. This study demonstrates the importance of these two important factors in describing binding of key catalytic intermediates

Dissociation of O2 molecules on strained Pb(111) surfaces

By performing first-principles molecular dynamics calculations, we systematically simulate the adsorption behavior of oxygen molecules on the clean and strained Pb(111) surfaces. The obtained molecular adsorption precursor state, and the activated dissociation process for oxygen molecules on the clean Pb surface are in good agreements with our previous static calculations, and perfectly explains previous experimental observations [Proc. Natl. Acad. Sci. U.S.A. 104, 9204 (2007)]. In addition, we also study the influences of surface strain on the dissociation behaviors of O2 molecules. It is found that on the compressed Pb(111) surfaces with a strain value of larger than 0.02, O2 molecules will not dissociate at all. And on the stretched Pb(111) surfaces, O2 molecules become easier to approach, and the adsorption energy of the dissociated oxygen atoms is larger than that on the clean Pb surface

The dynamics of adsorption on clean and adsorbate-modified transition metal surfaces. [Progress report, 1989--1991]

Research is being carried out on both nondissociative and dissociative adsorption of gases on transition metal surfaces, with emphasis on alkanes. Particular attention is be placed on understanding the effects of adsorbed species on adsorption probabilities and on clarifying the role of energy exchange processes at the surface in both dissociative and nondissociative adsorption. Molecular beam methods are coupled with methods of surface science to gain the greatest control of the variables of the problem, including the incident kinetic energy, vibrational energy and angle of incidence of the incoming molecules. The dynamics of both direct and precursor-influenced dissociative adsorption routes are examined. Surface intermediates formed by activated adsorption are identified by vibrational spectroscopy and temperature programmed reaction. Emphasis is on comparative studies of low molecular weight alkanes in order to understand the origin of the differences in their reactivities on different metals

Growth, electronic properties and reactivity of vanadium deposited onto a thin alumina film

The interaction of metals with oxide surfaces plays an important role in the manner of growth of the metal/oxide interface and eventually for the electronic properties and chemical reactivity of the resultant surface. We have investigated such effects for vanadium on alumina. By using a thin alumina film grown on a NiAl(110) as a model substrate, we were able to apply scanning tunneling microscopy (STM) as well as electron spectroscopic techniques without charging problems. According to our STM results, vanadium deposition at 300 K results in the formation of small thin particles/islands partly incorporated into the film at low coverages. With increasing coverage three-dimensional growth is found. The thermal stability and the growth behaviour of these nuclei at elevated deposition temperatures (≥600 K) are in agreement with a strong metal substrate interaction. In the coverage regime below 0.1 ML, X-ray photoelectron and X-ray absorption spectroscopy data provide evidence that the deposits are oxidized to Vx+, 1<x<2. Furthermore, we have studied the interaction at 720 K and in an ambient atmosphere of oxygen in order to check how vanadium reacts with the alumina film under more severe conditions. In fact, a thickening of the alumina film has been observed, which we ascribe to a catalytic effect of vanadia on the alumina film growth