Spatially Resolved Chemistry on Bimetallic Surfaces

Behm, R. J.

doi:10.12693/aphyspola.93.259

Cited by 37 publications

(21 citation statements)

References 33 publications

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“…This may lead to subsequent lower equilibrium coverage of CO and/or a higher rate of CO desorption. Again, both experimental [14,19] and theoretical [ 16± 18, 20±23] verification of this mechanism have been observed.…”

Section: Introductionmentioning

confidence: 70%

The Ligand Effect: CO Desorption from Pt/Ru Catalysts

et al. 2005

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Density Functional Theory (DFT) calculations of the adsorption energy of CO, for a platinum overlayer on Ru(0001), have been performed. For all coverages a significant reduction in the binding energy of up to 0.5 eV has been observed compared to that obtained on Pt(111). In addition, a Steady‐State Isotopic Transient Kinetic Analysis (SSITKA) study has been performed to determine the desorption rate dependence on the partial pressure of CO over commercial Pt/Ru electrocatalysts. As expected, no significant difference in the rate of exchange of CO at any given pressure is observed on going from Pt to Pt/Ru electrocatalysts when the diluted gas used was argon since the CO states will be filled to the same desorption energy for the two catalysts. However on changing the diluent gas to hydrogen, a reduction in the exchange rate for CO is observed clearly reflecting the lower CO binding energy and the increased competition for sites at the surface of the catalyst. The reduction efficiency of the Pt/Ru electrocatalyst was also studied and found to be highly dependent on whether CO or hydrogen was used. These results will be discussed with reference to the anode catalysis of the Polymer Electrolyte Membrane Fuel Cell (PEMFC).

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Section: Introductionmentioning

confidence: 70%

The Ligand Effect: CO Desorption from Pt/Ru Catalysts

et al. 2005

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“…A correlation between the d-band center of transition metal and alloy surfaces and the chemisorption energy of CO and other small molecules has been established [32,34]. Enhanced CO adsorption energies at surface defect sites of bimetallic surfaces, such as atomic step edges or kinks, has been found recently, which was attributed to the reduced coordination of these metal sites [35][36][37].…”

Section: Adsorption Processmentioning

confidence: 97%

“…The ultimate goal is to prepare surfaces with different well-defined concentrations of non-ideal defect structures. Such surfaces were prepared successfully by homo-and heteroepitaxy for some metals and bimetals and studied with respect to their adsorption properties [35,37], for metal-oxides, we are still at the beginning.…”

Section: Preparation Of Ordered Metal-oxide Surfacesmentioning

confidence: 99%

Surface chemistry and catalysis on well-defined epitaxial iron-oxide layers

Weiß

Ranke

2002

Progress in Surface Science

584

610

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Metal-oxide based catalysts are used for many important synthesis reactions in the chemical industry. A better understanding of the catalyst operation can be achieved by studying elemantary reaction steps on well-defined model catalyst systems. For the dehydrogenation of ethylbenzene to styrene in the presence of steam both unpromoted and potassium promoted iron-oxide catalysts are active. Here we review the work done over unpromoted single-crystalline FeO(111), Fe 3 O 4 (111) and α-Fe 2 O 3 (0001) films grown epitaxially on Pt(111) substrates. Their geometric and electronic surface structures were characterized by STM, LEED, electron microscopy and electron spectroscopic techniques. In an integrative approach, the interaction of water, ethylbenzene and styrene with these films was investigated mainly by thermal desorption and photoelectron emission spectroscopy. The adsorptiondesorption energetics and kinetics depend on the oxide surface terminations and are correlated to the electronic structures and acid-base properties of the corresponding oxide phases, which reveal insight into the nature of the active sites and into the catalytic function of semiconducting oxides in general. Catalytic studies, using a batch reactor arrangement at high gas pressures and post reaction surface analysis, showed that only α-Fe 2 O 3 (0001) containing surface defects is catalytically active, whereas Fe 3 O 4 (111) is always inactive. This can be related to the elementary adsorption and desorption properties observed in ultrahigh vacuum, which indicates that the surface chemical properties of the iron-oxide films do not change significantly across the "pressure-gap". A model is proposed according to which the active site involves a regular acidic surface sites and a defect site next to it. The results on metal-oxide surface chemistry also have implications for other fields, such as environmental science, biophysics and chemical sensors.-2 -"2kyEi9FYSQjBVrZxIPQ.FHIAC_WRa02_review.doc", Datum: 19.02.03

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“…It explains trends in reactivity from one transition metal to the next, and the effects of alloying, structure, strain, defects, and so forth. A large number of calculated and experimental results have been accounted for in this way (22)(23)(24)(25)(26)(27)(28)(29)(30)(31)(32)(33)(34)(35)(36). An example of experimental results explained by the d-band model is included in Fig.…”

Section: Density Functional Theory Calculations Of Surface Chemistrymentioning

confidence: 99%

Density functional theory in surface chemistry and catalysis

Nørskov

Abild‐Pedersen

Studt

et al. 2011

Proc. Natl. Acad. Sci. U.S.A.

1,956

1,342

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Recent advances in the understanding of reactivity trends for chemistry at transition-metal surfaces have enabled in silico design of heterogeneous catalysts in a few cases. The current status of the field is discussed with an emphasis on the role of coupling theory and experiment and future challenges. S urface chemistry is interesting and challenging for several reasons. It takes place at the border between the solid state and the liquid or gas phase and can be viewed as a meeting place between condensed-matter physics and chemistry. The phenomena at the solid-gas or solid-liquid interface are complicated for this reason. A chemical reaction at a metal surface, for instance, has all of the complexity of ordinary gas-phase reactions, but in addition the usual electron conservation rules do not apply because the metal provides a semi-infinite source of electrons at the Fermi level. A new set of concepts therefore needs to be developed to describe surface chemistry.An understanding of surface chemical reactions is necessary to describe a large number of surface phenomena including semiconductor processing, corrosion, electrochemistry, and heterogeneous catalysis. Heterogeneous catalysis alone has been estimated to be a prerequisite for more than 20% of all production in the industrial world (1), and it will most likely gain further importance in the years to come. The development of sustainable energy solutions represents one of the most important scientific and technical challenges of our time, and heterogeneous catalysis is at the heart of the problem. Most sustainable energy systems rely on the energy influx from the sun. Sunlight is diffuse and intermittent, and it is therefore essential to be able to store the energy, for example chemically as a fuel or in a battery. Such storage can then provide energy for the transportation sector and in decentralized applications, as it evens out temporal variations (2, 3). The key to providing an efficient transformation of energy to a chemical form or from one chemical form into another is the availability of suitable catalysts. In essentially all possible sustainable energy technologies, the lack of efficient and economically viable catalysts is a primary factor limiting their use (3, 4).In the present paper, we will discuss the status of the development of an understanding of surface chemistry. We will do this from a theoretical perspective, but it is important to stress that it is a close coupling between theory and experiment which has enabled the developments thus far. Surface science experiments have been invaluable in providing a quantitative description of a range of surface phenomena (5-14). This has been essential in benchmarking computational surface science based on density functional theory (DFT) calculations and in providing experimental guidance and verification of the concepts developed. This forms a good background for the development of an understanding of heterogeneous catalysis, which is the other part of this paper. We will show how the concepts dev...

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Spatially Resolved Chemistry on Bimetallic Surfaces

Cited by 37 publications

References 33 publications

The Ligand Effect: CO Desorption from Pt/Ru Catalysts

The Ligand Effect: CO Desorption from Pt/Ru Catalysts

Surface chemistry and catalysis on well-defined epitaxial iron-oxide layers

Density functional theory in surface chemistry and catalysis

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