Structure–Activity Correlations on Rh/Al2O3 and Rh/TiO2 Thin Film Model Catalysts after Oxidation and Reduction

Rupprechter, Günther; Seeber, Gernot; Goller, Hans; Hayek, K.

doi:10.1006/jcat.1999.2555

Cited by 62 publications

(41 citation statements)

References 49 publications

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“…[37] In that study it was observed that after oxidation at 575 K, the Rh metal particle surface was surrounded by a 1 nm oxidic layer, as evident in high-resolution images, while oxidation at higher temperature (725 K) resulted in the formation of a shell of hexagonal α-Rh 2 O 3 epitaxially covering the remaining Rh metal core, i.e., just the opposite situation as in the case of PdO/Pd. In analogy, a kinetically stable O-Rh-O trilayer surface oxide was observed during oxidation of a Rh(111) surface, [38] while three-dimensional PdO island growth was observed by atomic force microscope (AFM) imaging of Pd films annealed in O 2 at 1173 K. [39] Hence, the growth of PdO and Rh 2 O 3 proceeds via different mechanisms and PdO growth involves the formation of distinct PdO islands and/or crystallites rather than the formation of a thin adhesive layer.…”

Section: Aformation Of the Pdo Phasementioning

confidence: 90%

Growth and decomposition of aligned and ordered PdO nanoparticles

Penner

Wang

Jenewein

et al. 2006

The Journal of Chemical Physics

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The formation, thermal decomposition, and reduction of small PdO particles were studied by high-resolution transmission electron microscopy and selected area electron diffraction. Welldefined Pd particles (mean size of 5-7 nm) were grown epitaxially on NaCl (001) surfaces and subsequently covered by a layer of amorphous SiO 2 (25 nm), prepared by reactive deposition of SiO in 10 -2 Pa O 2 . The resulting films were exposed to molecular O 2 in the temperature range of 373-673 K, and the growth of PdO was studied. The formation of a PdO phase starts at 623 K and is almost completed at 673 K. The high-resolution experiments suggest a topotactic growth of PdO crystallites on top of the original Pd particles. Subsequent reaction of the PdO in 10 mbar CO for 15 min and thermal decomposition in 1 bar He for 1 h were also investigated in the temperature range from 373 to 573 K. Reductive treatments in CO up to 493 K do not cause a significant change in the PdO structure. The reduction of PdO starts at 503 K and is completed at 523 K. In contrast, PdO decomposes in 1 bar He at around 573 K. The mechanism of PdO growth and decay is discussed and compared to results of previous studies on other metals, e.g., on rhodium.

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Section: Aformation Of the Pdo Phasementioning

confidence: 90%

Growth and decomposition of aligned and ordered PdO nanoparticles

Penner

Wang

Jenewein

et al. 2006

The Journal of Chemical Physics

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“…In addition, by growing dispersed Pt particles with a common crystalline orientation and regular shapes as the initial state, more information about structural and morphological changes is obtained, which helps to reveal new mechanisms involved in the metal support interaction. 3 Si. Moreover, electron diffraction from many particles after the reduction still exhibits spots from Pt 3 Si in the same azimuth orientation as those from Pt.…”

Section: Discussionmentioning

confidence: 99%

“…Among all the Pt silicides, the cubic Pt 3 Si was reported to have an L1 2 (Cu 3 Au) structure with space group m 3 Pm , and its lattice parameter, a = 3.88 Å, is decreased by only 1 % with respect to that of Pt, a 0 = 3.92 Å. The monoclinic Pt 3 Si phase has space group C2/m and the lattice parameters a = 7.702 Å, b = c = 7.765 Å and β = 88°11′ [19]. It can be regarded as a distorted Cu 3 Au structure.…”

Section: Introductionmentioning

confidence: 99%

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Silicide formation on a Pt/SiO2 model catalyst studied by TEM, EELS, and EDXS

Wang

Penner

Rupprechter

et al. 2003

Journal of Catalysis

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Dispersed Pt particles supported by amorphous SiO2 were grown with regular shapes and orientation along the same crystallographic axis ("initial state"). After an oxidising treatment the samples were heated in 1 bar hydrogen at 873 K. The morphological and structural changes were studied by transmission electron microscopy (TEM). Platinum silicide Pt3Si with L12 (Cu3Au) structure, monoclinic Pt3Si and tetragonal Pt12Si5 were identified after the treatment. A topotactic structural transformation accompanied by the migration of Si from the substrate to the particles is suggested to take place during Pt3Si formation. Pt12Si5 is formed through melting and recrystallisation. The mechanisms of reconstruction of the crystallites are discussed.

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“…When the turnover rates for CO oxidation, for example, is measured continuously in the same time, the hot electron current is measured and the hot electron current and the turnover rate for the reaction are correlated [58] . This implies that the activity at the oxide metal surface in certain catalytic reactions which is often called as "strong metal-support interaction [59][60][61] " can be associated with the hot electron flow at oxide-metal interface.…”

Section: Oxide Metal Interfaces Are Catalytically Activementioning

confidence: 99%

Evolution of the surface science of catalysis from single crystals to metal nanoparticles under pressure

Somorjai

Park

2008

The Journal of Chemical Physics

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Vacuum studies of metal single crystal surfaces using electron and molecular beam scattering revealed that the surface atoms relocate when the surface is clean (reconstruction) and when it is covered by adsorbates (adsorbate induced restructuring).It was also discovered that atomic steps and other low coordination surface sites are active for breaking chemical bonds (H-H, O=O, C-H, C=O and C-C) with high reaction probability. Investigations at high reactant pressures using sum frequency generation (SFG) -vibrational spectroscopy and high pressure scanning tunneling microscopy (HPSTM) revealed bond breaking at low reaction probability sites on the adsorbatecovered metal surface, and the need for adsorbate mobility for continued turnover. Since most catalysts (heterogeneous, enzyme and homogeneous) are nanoparticles, colloid synthesis methods were developed to produce monodispersed metal nanoparticles in the 1-10 nm range and controlled shapes to use them as new model catalyst systems in twodimensional thin film form or deposited in mesoporous three-dimensional oxides. Studies of reaction selectivity in multipath reactions (hydrogenation of benzene, cyclohexene and crotonaldehyde) showed that reaction selectivity depends on both nanoparticle size and shape. The oxide-metal nanoparticle interface was found to be an important catalytic site because of the hot electron flow induced by exothermic reactions like carbon monoxide oxidation.

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Structure–Activity Correlations on Rh/Al2O3 and Rh/TiO2 Thin Film Model Catalysts after Oxidation and Reduction

Cited by 62 publications

References 49 publications

Growth and decomposition of aligned and ordered PdO nanoparticles

Growth and decomposition of aligned and ordered PdO nanoparticles

Silicide formation on a Pt/SiO2 model catalyst studied by TEM, EELS, and EDXS

Evolution of the surface science of catalysis from single crystals to metal nanoparticles under pressure

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