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Ploner K, Schlicker L, Gili A, Gurlo A, Doran A, Zhang L, Armbrüster M, Obendorf D, Bernardi J, Klötzer B, Penner S. Reactive metal-support interaction in the Cu-In 2O 3 system: intermetallic compound formation and its consequences for CO 2-selective methanol steam reforming. SCIENCE AND TECHNOLOGY OF ADVANCED MATERIALS 2019; 20:356-366. [PMID: 31068984 PMCID: PMC6493314 DOI: 10.1080/14686996.2019.1590127] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 01/11/2019] [Revised: 02/27/2019] [Accepted: 02/28/2019] [Indexed: 06/09/2023]
Abstract
The reactive metal-support interaction in the Cu-In2O3 system and its implications on the CO2 selectivity in methanol steam reforming (MSR) have been assessed using nanosized Cu particles on a powdered cubic In2O3 support. Reduction in hydrogen at 300 °C resulted in the formation of metallic Cu particles on In2O3. This system already represents a highly CO2-selective MSR catalyst with ~93% selectivity, but only 56% methanol conversion and a maximum H2 formation rate of 1.3 µmol gCu -1 s-1. After reduction at 400 °C, the system enters an In2O3-supported intermetallic compound state with Cu2In as the majority phase. Cu2In exhibits markedly different self-activating properties at equally pronounced CO2 selectivities between 92% and 94%. A methanol conversion improvement from roughly 64% to 84% accompanied by an increase in the maximum hydrogen formation rate from 1.8 to 3.8 µmol gCu -1 s-1 has been observed from the first to the fourth consecutive runs. The presented results directly show the prospective properties of a new class of Cu-based intermetallic materials, beneficially combining the MSR properties of the catalyst's constituents Cu and In2O3. In essence, the results also open up the pathway to in-depth development of potentially CO2-selective bulk intermetallic Cu-In compounds with well-defined stoichiometry in MSR.
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Suchorski Y, Datler M, Bespalov I, Zeininger J, Stöger-Pollach M, Bernardi J, Grönbeck H, Rupprechter G. Surface-Structure Libraries: Multifrequential Oscillations in Catalytic Hydrogen Oxidation on Rhodium. THE JOURNAL OF PHYSICAL CHEMISTRY. C, NANOMATERIALS AND INTERFACES 2019; 123:4217-4227. [PMID: 31057690 PMCID: PMC6494118 DOI: 10.1021/acs.jpcc.8b11421] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/26/2018] [Revised: 01/18/2019] [Indexed: 05/18/2023]
Abstract
Multifrequential oscillating spatiotemporal patterns in the catalytic hydrogen oxidation on rhodium have been observed in situ in the 10-6 mbar pressure range using photoemission electron microscopy. The effect is manifested by periodic chemical waves, which travel over the polycrystalline Rh surface and change their oscillation frequency while crossing boundaries between different Rh(hkl) domains. Each crystallographically specific μm-sized Rh(hkl) domain exhibits an individual wave pattern and oscillation frequency, despite the global diffusional coupling of the surface reaction, altogether creating a structure library. This unique reaction behavior is attributed to the ability of stepped surfaces of high-Miller-index domains to facilitate the formation of subsurface oxygen, serving as a feedback mechanism of kinetic oscillations. Formation of a network of subsurface oxygen as a result of colliding reaction fronts was observed in situ. Microkinetic model analysis was used to rationalize the observed effects and to reveal the relation between the barriers for surface oxidation and oscillation frequency. Structural limits of the oscillations, the existence range of oscillations, as well as the effect of varying hydrogen pressure are demonstrated.
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Hauser D, Auer A, Kunze-Liebhäuser J, Schwarz S, Bernardi J, Penner S. Hybrid synthesis of zirconium oxycarbide nanopowders with defined and controlled composition. RSC Adv 2019; 9:3151-3156. [PMID: 30931107 PMCID: PMC6394884 DOI: 10.1039/c8ra09584a] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2018] [Accepted: 01/17/2019] [Indexed: 01/17/2023] Open
Abstract
A combined synthesis strategy involving a carbothermal reduction and gelation approach with glycine as gelating agent was used to obtain Zr-based (oxy)carbide materials with defined and controlled composition. A comparatively low temperature approach (1500 °C) allows exploration of the ZrC–ZrO2 phase diagram and reproducibly leads to zirconium (oxy)carbide phases with different C/Zr ratios, as confirmed by combined X-ray diffraction (XRD) and transmission electron microscopy (TEM) data. The latter also indicates a chemically very homogeneous distribution of oxygen and carbon throughout the sample bulk, a prerequisite for further characterization of its intrinsic physico-chemical properties. Due to the general variability of the synthesis procedure – variation of metal precursor, amount of gelating agent and carbon precursor source – it is expected that the method can be easily adapted and transferred to other metal – oxycarbide materials. A combined synthesis strategy involving a carbothermal reduction and gelation approach with glycine as gelating agent was used to obtain Zr-based (oxy)carbide materials with defined and controlled composition.![]()
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Götsch T, Köpfle N, Grünbacher M, Bernardi J, Carbonio EA, Hävecker M, Knop-Gericke A, Bekheet MF, Schlicker L, Doran A, Gurlo A, Franz A, Klötzer B, Penner S. Crystallographic and electronic evolution of lanthanum strontium ferrite (La0.6Sr0.4FeO3−δ) thin film and bulk model systems during iron exsolution. Phys Chem Chem Phys 2019; 21:3781-3794. [DOI: 10.1039/c8cp07743f] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
We study the changes in the crystallographic phases and in the chemical states during the iron exsolution process of lanthanum strontium ferrite (LSF, La0.6Sr0.4FeO3−δ).
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Thomele D, Gheisi AR, Niedermaier M, Elsässer MS, Bernardi J, Grönbeck H, Diwald O. Thin water films and particle morphology evolution in nanocrystalline MgO. JOURNAL OF THE AMERICAN CERAMIC SOCIETY. AMERICAN CERAMIC SOCIETY 2018; 101:4994-5003. [PMID: 30333631 PMCID: PMC6175089 DOI: 10.1111/jace.15775] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/15/2017] [Accepted: 05/05/2018] [Indexed: 05/29/2023]
Abstract
A key question in the field of ceramics and catalysis is how and to what extent residual water in the reactive environment of a metal oxide particle powder affects particle coarsening and morphology. With X-ray Diffraction (XRD) and Transmission Electron Microscopy (TEM), we investigated annealing-induced morphology changes on powders of MgO nanocubes in different gaseous H2O environments. The use of such a model system for particle powders enabled us to describe how adsorbed water that originates from short exposure to air determines the evolution of MgO grain size, morphology, and microstructure. While cubic nanoparticles with a predominant abundance of (100) surface planes retain their shape after annealing to T = 1173 K under continuous pumping with a base pressure of water p(H2O) = 10-5 mbar, higher water partial pressures promote mass transport on the surfaces and across interfaces of such particle systems. This leads to substantial growth and intergrowth of particles and simultaneously favors the formation of step edges and shallow protrusions on terraces. The mass transfer is promoted by thin films of water providing a two-dimensional solvent for Mg2+ ion hydration. In addition, we obtained direct evidence for hydroxylation-induced stabilization of (110) faces and step edges of the grain surfaces.
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Götsch T, Ploner K, Bernardi J, Schlicker L, Gili A, Doran A, Gurlo A, Penner S. Formation of Pd-Ce intermetallic compounds by reductive metal-support interaction. J SOLID STATE CHEM 2018. [DOI: 10.1016/j.jssc.2018.05.036] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/14/2022]
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Suchorski Y, Datler M, Bespalov I, Zeininger J, Stöger-Pollach M, Bernardi J, Grönbeck H, Rupprechter G. Visualizing catalyst heterogeneity by a multifrequential oscillating reaction. Nat Commun 2018; 9:600. [PMID: 29426883 PMCID: PMC5807506 DOI: 10.1038/s41467-018-03007-3] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2017] [Accepted: 01/12/2018] [Indexed: 11/23/2022] Open
Abstract
It is well documented that different surface structures of catalytically active metals may exhibit different catalytic properties. This is typically examined by comparing the catalytic activities and/or selectivities of various well-defined smooth and stepped/kinked single crystal surfaces. Here we report the direct observation of the heterogeneity of active polycrystalline surfaces under reaction conditions, which is manifested by multifrequential oscillations during hydrogen oxidation over rhodium, imaged in situ by photoemission electron microscopy. Each specific surface structure, i.e. the crystallographically different µm-sized domains of rhodium, exhibits an individual spiral pattern and oscillation frequency, despite the global diffusional coupling of the surface reaction. This reaction behavior is attributed to the ability of stepped surfaces of high-Miller-index domains to facilitate the formation of subsurface oxygen, serving as feedback mechanism of the observed oscillations. The current experimental findings, backed by microkinetic modeling, may open an alternative approach towards addressing the structure-sensitivity of heterogeneous surfaces.
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Yakymovych A, Kaptay G, Flandorfer H, Bernardi J, Schwarz S, Ipser H. The nano heat effect of replacing macro-particles by nano-particles in drop calorimetry: the case of core/shell metal/oxide nano-particles. RSC Adv 2018; 8:8856-8869. [PMID: 35539825 PMCID: PMC9078637 DOI: 10.1039/c7ra13643a] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/25/2017] [Accepted: 02/20/2018] [Indexed: 11/21/2022] Open
Abstract
Difference in the enthalpy effect by replacing micro- by nano-sized particles in drop calorimetry.
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Salihovic M, Hüsing N, Bernardi J, Presser V, Elsaesser MS. Carbon aerogels with improved flexibility by sphere templating. RSC Adv 2018; 8:27326-27331. [PMID: 35539967 PMCID: PMC9083318 DOI: 10.1039/c8ra04848g] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2018] [Accepted: 07/24/2018] [Indexed: 11/21/2022] Open
Abstract
Using soft templating, mechanically reversible compressible resorcinol–formaldehyde aerogels can be converted into mechanically reversible compressible carbon aerogels with high surface area by carbonization in an inert atmosphere.
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Navickas E, Chen Y, Lu Q, Wallisch W, Huber TM, Bernardi J, Stöger-Pollach M, Friedbacher G, Hutter H, Yildiz B, Fleig J. Dislocations Accelerate Oxygen Ion Diffusion in La 0.8Sr 0.2MnO 3 Epitaxial Thin Films. ACS NANO 2017; 11:11475-11487. [PMID: 28981249 PMCID: PMC5707630 DOI: 10.1021/acsnano.7b06228] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/01/2017] [Accepted: 10/05/2017] [Indexed: 05/24/2023]
Abstract
Revealing whether dislocations accelerate oxygen ion transport is important for providing abilities in tuning the ionic conductivity of ceramic materials. In this study, we report how dislocations affect oxygen ion diffusion in Sr-doped LaMnO3 (LSM), a model perovskite oxide that serves in energy conversion technologies. LSM epitaxial thin films with thicknesses ranging from 10 nm to more than 100 nm were prepared by pulsed laser deposition on single-crystal LaAlO3 and SrTiO3 substrates. The lattice mismatch between the film and substrates induces compressive or tensile in-plane strain in the LSM layers. This lattice strain is partially reduced by dislocations, especially in the LSM films on LaAlO3. Oxygen isotope exchange measured by secondary ion mass spectrometry revealed the existence of at least two very different diffusion coefficients in the LSM films on LaAlO3. The diffusion profiles can be quantitatively explained by the existence of fast oxygen ion diffusion along threading dislocations that is faster by up to 3 orders of magnitude compared to that in LSM bulk.
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Ploner K, Götsch T, Kogler G, Thalinger R, Bernardi J, Zhao Q, Zhuo C, Klötzer B, Penner S. Structural and Catalytic Properties of Ag- and Co3O4-Impregnated Strontium Titanium Ferrite SrTi0.7Fe0.3O3−δ in Methanol Steam Reforming. Ind Eng Chem Res 2017. [DOI: 10.1021/acs.iecr.7b03778] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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Putz F, Morak R, Elsaesser MS, Balzer C, Braxmeier S, Bernardi J, Paris O, Reichenauer G, Hüsing N. Setting Directions: Anisotropy in Hierarchically Organized Porous Silica. CHEMISTRY OF MATERIALS : A PUBLICATION OF THE AMERICAN CHEMICAL SOCIETY 2017; 29:7969-7975. [PMID: 28989232 PMCID: PMC5627989 DOI: 10.1021/acs.chemmater.7b03032] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/19/2017] [Revised: 08/31/2017] [Indexed: 05/29/2023]
Abstract
Structural hierarchy, porosity, and isotropy/anisotropy are highly relevant factors for mechanical properties and thereby the functionality of porous materials. However, even though anisotropic and hierarchically organized, porous materials are well known in nature, such as bone or wood, producing the synthetic counterparts in the laboratory is difficult. We report for the first time a straightforward combination of sol-gel processing and shear-induced alignment to create hierarchical silica monoliths exhibiting anisotropy on the levels of both, meso- and macropores. The resulting material consists of an anisotropic macroporous network of struts comprising 2D hexagonally organized cylindrical mesopores. While the anisotropy of the mesopores is an inherent feature of the pores formed by liquid crystal templating, the anisotropy of the macropores is induced by shearing of the network. Scanning electron microscopy and small-angle X-ray scattering show that the majority of network forming struts is oriented towards the shearing direction; a quantitative analysis of scattering data confirms that roughly 40% of the strut volume exhibits a preferred orientation. The anisotropy of the material's macroporosity is also reflected in its mechanical properties; i.e., the Young's modulus differs by nearly a factor of 2 between the directions of shear application and perpendicular to it. Unexpectedly, the adsorption-induced strain of the material exhibits little to no anisotropy.
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Wolfbeisser A, Kovács G, Kozlov SM, Föttinger K, Bernardi J, Klötzer B, Neyman KM, Rupprechter G. Surface composition changes of CuNi-ZrO2 during methane decomposition: An operando NAP-XPS and density functional study. Catal Today 2017. [DOI: 10.1016/j.cattod.2016.04.022] [Citation(s) in RCA: 41] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
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Hayati-Roodbari N, Berger RJF, Bernardi J, Kinge S, Hüsing N, Elsaesser MS. Monolithic porous magnesium silicide. Dalton Trans 2017; 46:8855-8860. [DOI: 10.1039/c7dt00571g] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Macroporous magnesium silicide monoliths were prepared by a two-step magnesiothermic reaction starting from hierarchically structured silica with silicon as an intermediate step.
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Thomele D, Bourret GR, Bernardi J, Bockstedte M, Diwald O. Hydroxylation Induced Alignment of Metal Oxide Nanocubes. Angew Chem Int Ed Engl 2016; 56:1407-1410. [PMID: 28005313 DOI: 10.1002/anie.201608538] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2016] [Revised: 10/27/2016] [Indexed: 01/03/2023]
Abstract
Water vapor is ubiquitous under ambient conditions and may alter the shape of nanoparticles. How to utilize water adsorption for nanomaterial functionality and structure formation, however, is a yet unexplored field. Herein, we report the use of water vapor to induce the self-organization of MgO nanocubes into regularly staggered one-dimensional structures. This transformation evolves via an initial alignment of the MgO cubes, the formation of intermediate elongated Mg(OH)2 structures, and their reconversion into MgO cubes arranged in staggered structures. Ab initio DFT modelling identifies surface-energy changes associated with the cube surface hydration and hydroxylation to promote the uncommon staggered stacked assembly of the cubes. This first observation of metal oxide nanoparticle self-organization occurring outside a bulk solution may pave novel routes for inducing texture in ceramics and represents a great test-bed for new surface-science concepts.
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Thomele D, Bourret GR, Bernardi J, Bockstedte M, Diwald O. Organisation von Metalloxid‐Nanowürfeln durch Hydroxylierung. Angew Chem Int Ed Engl 2016. [DOI: 10.1002/ange.201608538] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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Wolfbeisser A, Sophiphun O, Bernardi J, Wittayakun J, Föttinger K, Rupprechter G. Methane dry reforming over ceria-zirconia supported Ni catalysts. Catal Today 2016. [DOI: 10.1016/j.cattod.2016.04.025] [Citation(s) in RCA: 166] [Impact Index Per Article: 20.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
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Kocsis K, Niedermaier M, Bernardi J, Berger T, Diwald O. Changing interfaces: Photoluminescent ZnO nanoparticle powders in different aqueous environments. SURFACE SCIENCE 2016; 652:253-260. [PMID: 32903287 PMCID: PMC7116034 DOI: 10.1016/j.susc.2016.02.019] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
We transformed vapor phase grown ZnO nanoparticle powders into aqueous ZnO nanoparticle dispersions and studied the impact of associated microstructure and interface property changes on their spectroscopic properties. With photoluminescence (PL) spectroscopy, we probed oxygen interstitials O i 2 - in the near surface region and tracked their specific PL emission response at hvEM = 2.1 eV during the controlled conversion of the solid-vacuum into the solid-liquid interface. While oxygen adsorption via the gas phase does affect the intensity of the PL emission bands, the O2 contact with ZnO nanoparticles across the solid-liquid interface does not. Moreover, we found that the near band edge emission feature at hvEM = 3.2 eV gains relative intensity with regard to the PL emission features in the visible light region. Searching for potential PL indicators that are specific to early stages of particle dissolution, we addressed for aqueous ZnO nanoparticle dispersions the effect of formic acid adsorption. In the absence of related spectroscopic features, we were able to consistently track ZnO nanoparticle dissolution and the concomitant formation of sol- vated Zinc formate species by means of PL and FT-IR spectroscopy, dynamic light scattering, and zeta potential measurements. For a more consistent and robust assessment of nanoparticle properties in different continuous phases, we discuss characterization challenges and potential pitfalls that arise upon replacing the solid-gas with the solid-liquid interface.
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Anic K, Wolfbeisser A, Li H, Rameshan C, Föttinger K, Bernardi J, Rupprechter G. Surface Spectroscopy on UHV-Grown and Technological Ni-ZrO 2 Reforming Catalysts: From UHV to Operando Conditions. Top Catal 2016; 59:1614-1627. [PMID: 28035177 PMCID: PMC5153820 DOI: 10.1007/s11244-016-0678-8] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Ni nanoparticles supported on ZrO2 are a prototypical system for reforming catalysis converting methane to synthesis gas. Herein, we examine this catalyst on a fundamental level using a 2-fold approach employing industrial-grade catalysts as well as surface science based model catalysts. In both cases we examine the atomic (HRTEM/XRD/LEED) and electronic (XPS) structure, as well as the adsorption properties (FTIR/PM-IRAS), with emphasis on in situ/operando studies under atmospheric pressure conditions. For technological Ni–ZrO2 the rather large Ni nanoparticles (about 20 nm diameter) were evenly distributed over the monoclinic zirconia support. In situ FTIR spectroscopy and ex situ XRD revealed that even upon H2 exposure at 673 K no full reduction of the nickel surface was achieved. CO adsorbed reversibly on metallic and oxidic Ni sites but no CO dissociation was observed at room temperature, most likely because the Ni particle edges/steps comprised Ni oxide. CO desorption temperatures were in line with single crystal data, due to the large size of the nanoparticles. During methane dry reforming at 873 K carbon species were deposited on the Ni surface within the first 3 h but the CH4 and CO2 conversion hardly changed even during 24 h. Post reaction TEM and TPO suggest the formation of graphitic and whisker-type carbon that do not significantly block the Ni surface but rather physically block the tube reactor. Reverse water gas shift decreased the H2/CO ratio. Operando studies of methane steam reforming, simultaneously recording FTIR and MS data, detected activated CH4 (CH3 and CH2), activated water (OH), as well as different bidentate (bi)carbonate species, with the latter being involved in the water gas shift side reaction. Surface science Ni–ZrO2 model catalysts were prepared by first growing an ultrathin “trilayer” (O–Zr–O) ZrO2 support on an Pd3Zr alloy substrate, and subsequently depositing Ni, with the process being monitored by XPS and LEED. Apart from the trilayer oxide, there is a small fraction of ZrO2 clusters with more bulk-like properties. When CO was adsorbed on the (fully metallic) Ni particles at pressures up to 100 mbar, both PM-IRAS and XPS indicated CO dissociation around room temperature and blocking of the Ni surface by carbon (note that on the partially oxidized technological Ni particles, CO dissociation was absent). The Ni nanoparticles were stable up to 550 K but annealing to higher temperatures induced Ni migration through the ultrathin ZrO2 support into the Pd3Zr alloy. Both approaches have their benefits and limitations but enable us to address specific questions on a molecular level.
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Mayr L, Klötzer B, Schmidmair D, Köpfle N, Bernardi J, Schwarz S, Armbrüster M, Penner S. Boosting Hydrogen Production from Methanol and Water by in situ Activation of Bimetallic Cu−Zr Species. ChemCatChem 2016. [DOI: 10.1002/cctc.201600361] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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Prokofiev A, Svagera R, Waas M, Weil M, Bernardi J, Paschen S. Mechanism of Rare Earth Incorporation and Crystal Growth of Rare Earth Containing Type-I Clathrates. CRYSTAL GROWTH & DESIGN 2016; 16:25-33. [PMID: 26823658 PMCID: PMC4718404 DOI: 10.1021/acs.cgd.5b00461] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 04/03/2015] [Revised: 12/02/2015] [Indexed: 06/05/2023]
Abstract
Type-I clathrates possess extremely low thermal conductivities, a property that makes them promising materials for thermoelectric applications. The incorporation of cerium into one such clathrate has recently been shown to lead to a drastic enhancement of the thermopower, another property determining the thermoelectric efficiency. Here we explore the mechanism of the incorporation of rare earth elements into type-I clathrates. Our investigation of the crystal growth and the composition of the phase Ba8-x RE x TM y Si46-y (RE = rare earth element; TM = Au, Pd, Pt) reveals that the RE content x is mainly governed by two factors, the free cage space and the electron balance.
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Datler M, Bespalov I, Buhr S, Zeininger J, Stöger-Pollach M, Bernardi J, Rupprechter G, Suchorski Y. Hydrogen Oxidation on Stepped Rh Surfaces: µm-Scale versus Nanoscale. Catal Letters 2016; 146:1867-1874. [PMID: 32355436 PMCID: PMC7175702 DOI: 10.1007/s10562-016-1824-4] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2016] [Accepted: 07/21/2016] [Indexed: 11/11/2022]
Abstract
Abstract The catalytic H2 oxidation reaction on stepped Rh surfaces in the 10−6 mbar pressure range was studied in situ on individual high-Miller-index domains of a polycrystalline Rh foil by PEEM (photoemission electron microscopy) and on a Rh nanotip by FIM/FEM (field-ion/field-emission microscopy). The activity, particularly the tolerance to poisoning by oxygen, was found to strongly depend on the density of steps and defects, as well as on the size of the catalytically active surfaces. Graphical Abstract ![]()
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Schneider J, Franke M, Gurrath M, Röckert M, Berger T, Bernardi J, Meyer B, Steinrück HP, Lytken O, Diwald O. Porphyrin Metalation at MgO Surfaces: A Spectroscopic and Quantum Mechanical Study on Complementary Model Systems. Chemistry 2015; 22:1744-9. [PMID: 26682774 DOI: 10.1002/chem.201503661] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2015] [Indexed: 11/05/2022]
Abstract
We show that both single-crystalline and nanostructured MgO surfaces convert free-base tetraphenyl porphyrin (2HTPP) into magnesium tetraphenyl porphyrin (MgTPP) at room temperature. The reaction can be viewed as an ion exchange between the two aminic protons of the 2HTPP molecule with a Mg(2+) ion from the surface. The driving force for the reaction is the strong stability of the formed hydroxyl groups along the steps and at defects on the MgO surface. We have used an integrated characterization approach that includes UV/Vis diffuse reflectance measurements on nanostructured powders, X-ray photoelectron spectroscopic investigation of atomically clean MgO(100) single-crystalline thin films, and density functional theory (DFT) calculations on model systems. The DFT calculations demonstrate that MgTPP formation is strongly exothermic at the corners, edges and steps, but slightly endothermic on terrace sites. This agrees well with the UV/Vis diffuse reflectance, which upon adsorption of 2HTPP shows a decrease in the absorption band associated with corner and edge sites on MgO nanocube powders.
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Luczynski KW, Steiger-Thirsfeld A, Bernardi J, Eberhardsteiner J, Hellmich C. Extracellular bone matrix exhibits hardening elastoplasticity and more than double cortical strength: Evidence from homogeneous compression of non-tapered single micron-sized pillars welded to a rigid substrate. J Mech Behav Biomed Mater 2015; 52:51-62. [DOI: 10.1016/j.jmbbm.2015.03.001] [Citation(s) in RCA: 53] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2014] [Revised: 02/13/2015] [Accepted: 03/01/2015] [Indexed: 11/17/2022]
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Sologub O, Salamakha L, Rogl P, Stöger B, Bauer E, Bernardi J, Giester G, Waas M, Svagera R. Pt–B System Revisited: Pt2B, a New Structure Type of Binary Borides. Ternary WAl12-Type Derivative Borides. Inorg Chem 2015; 54:10958-65. [DOI: 10.1021/acs.inorgchem.5b01998] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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